Opportunities in Wet-End Chemistry

Publications by Martin Hubbe and Group Members
Up-to-date listing and many article PDF files can be obtained from NC State University's "Repository" by using this link.

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Publication List with Abstracts


Tayeb, A. H., Rojas, O. J., and Hubbe, M. A. (2017). “Lipoxygenase-mediated peroxidation mechanism of lipids studied by 13C/1H NMR and FTIR spectroscopy,” Industrial Crops Prod. 104(1), 253-262.

Three unsaturated fatty acids, namely 9-cis,12-cis-linoleic acid, 1,2,3-tri-cis, cis-9,12-octadecadienoyl (glycerol trilinolein) and 1,2,3-tri-cis-9-octadecenoyl (triolein) were selected as models of components of plant extractives to monitor the hydroperoxygenation induced by soybean lipoxygenase (LOX), which was applied as an oxidative catalyst at room temperature. The fatty acids were monitored in colloidal dispersions in relation to their molecular changes using 1H/13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and UV spectroscopies. The detection of the hydroperoxy group was limited due to its unstable nature. However, the reduction of protons associated with the diene groups and the substitution of hydroperoxy groups at the allylic positon in conjugated lipids were detected by the induced chemical shift of HOO-bearing 13C and 1H resonances and the oxygen absorption owing to changes in the molecule. Moreover, compared to the two other substrates, no oxygen substitution was observed in triolein, in accordance with its lower level of saturation and the absence of bis-allylic carbon. Our results are of relevance to plant fiber processing, since fatty acids are major constituents of hydrophobic deposits that cause a range of manufacturing challenges.

Tayeb, A. H., Hubbe, M. A., Zhang, Y. X., and Rojas, O. J. (2017). “Effect of lipoxygenase oxidation on surface deposition of unsaturated fatty acids,” Langmuir 33(18), 4559-4566. DOI: 10.1021/acs.langmuir.7b00908

We studied the interactions of lipid molecules (linoleic acid, glycerol trilinoleate and a complex mixture of wood extractives) with hydrophilic and hydrophobic surfaces (cellulose nanofibrils, CNF, and polyethylene terephthalate, PET, respectively). The effect of lipoxygenase treatment to minimize the affinity of the lipids with the given surface was considered. Application of an electroacoustic sensing technique (QCM) allowed the monitoring of the kinetics of oxidation as well as dynamics of lipid deposition on CNF and PET. The effect of the lipoxygenase enzymes (LOX) was elucidated with regards to their ability to reduce the formation of soiling lipid layers. The results pointed to the fact that the rate of colloidal oxidation depended on the type of lipid substrate. The pre-treatment of the lipids with LOX reduced substantially their affinity to the surfaces, especially PET. Surface plasmon resonance (SPR) sensograms confirmed the effect of oxidation in decreasing the extent of deposition on the hydrophilic CNF. QCM energy dissipation analyses revealed the possible presence of a loosely adsorbed lipid layer on the PET surface. The morphology of the deposits accumulated on the solids was determined by atomic force microscopy and indicated important changes upon lipid treatment with LOX. The results highlighted the benefit of enzyme as a bio-based treatment to reduce hydrophobic interactions, thus providing a viable solution to the control of lipid deposition from aqueous media.

Hubbe, M. A. (2017). “Hybrid filler (cellulose/noncellulose) reinforced nanocomposites,” in: Handbook of Nanocellulose and Cellulose Nanocomposites, Vol. 1, H. Kargarzadeh, I. Ahmad, S. Thomas, and A. Dufresne (eds.), Wiley-VCH, Ch. 8, pp. 273-299,

This chapter considers studies in which two different kinds of solid filler materials are used simultaneously as reinforcements in an effort to improve various performance attributes of a polymeric matrix.  As in the case of a hybrid vehicle, one having both an electric and a gasoline engine, the two reinforcing elements ought to provide unique combinations of properties or synergistic effects.  The term “hybrid composite” also can be employed when two different materials are combined together in the preparation of a hybrid reinforcing element, which then can be used in the manufacture of a composite.  The systems to be discussed in this chapter will be limited to cases in which one of the two reinforcing elements is cellulose-based.  In most of the work to be discussed, the non-cellulosic reinforcement is an inorganic material such as a specialized clay product or finely chopped glass fiber.

Hubbe, M. A., Smith, R. D., Zou, X., Katuscak, S., Potthast, A., and Ahn, K. (2017). "Deacidification of acidic books and paper by means of non-aqueous dispersions of alkaline particles: A review focusing on completeness of the reaction," BioResources 12(2), 4410-4477.

Deacidification refers to chemical treatments meant to slow down the acid hydrolysis and embrittlement of books and paper documents that had been printed on acidic paper. From the early 1800s up to about 1990, papermakers used aluminum sulfate, an acidic compound, in most printing papers. Certain deacidification methods use non-aqueous media to distribute alkaline mineral particles such as MgO within the pages of the treated books. Evidence is considered here as to whether or not the proximity of alkaline particles within such documents is sufficient to neutralize the acidic species present. Because much evidence suggests incomplete neutralization, a second focus concerns what to do next in cases where book already have been treated with a non-aqueous dispersion system.  Based on the literature, the neutralization of acidic species within such paper can be completed by partial moistening, by high humidity and pressure, by water condensation, as well as by optional treatments to enhance paper strength and a final drying step.

Hubbe, M. A., Ferrer, A., Tyagi, P., Yin, Y., Salas, C., Pal, L., and Rojas, O. J. (2017). "Nanocellulose in thin films, coatings, and plies for packaging applications: A review," BioResources 12(1), 2143-2233.

This review article was prompted by a remarkable growth in the number of scientific publications dealing with the use of nanocellulose (especially nanofibrillated cellulose (NFC), cellulose nanocrystals (CNC), and bacterial cellulose (BC)) to enhance the barrier properties and other performance attributes of new generations of packaging products.  Recent research has confirmed and extended what is known about oxygen barrier and water vapor transmission performance, strength properties, and the susceptibility of nanocellulose-based films and coatings to the presence of humidity or moisture.  Recent research also points to various promising strategies to prepare ecologically-friendly packaging materials, taking advantage of nanocellulose-based layers, to compete in an arena that has long been dominated by synthetic plastics.  Some promising approaches entail usage of multiple layers of different materials or additives such as waxes, high-aspect ratio nano-clays, and surface-active compounds in addition to the nanocellulose material.  While various high-end applications may be achieved by chemical derivatization or grafting of the nanocellulose, the current trends in research suggest that high-volume implementation will likely incorporate water-based formulations, which may include

Farhat, W., Venditti, R. A., Hubbe, M., Taha, M., Becquart, F., and Ayoub, A. (2017). “A review of water-resistant hemicellulose-based materials: Processing and applications,” ChemSusChem 10, 305-323. DOI: 10.1002/cssc.201601047

Due to their hydrophilic nature, hemicelluloses may tend to be overlooked as the main ingredient for water-resistant product applications. However, their domains of use can be greatly expanded by chemical derivatization.  The present review article considers research in which hydrophobic derivatives of hemicelluloses or combinations of hemicelluloses with hydrophobic materials have shown promise in preparation of films and composites.  The review also will cover research publications dealing with isolation methods that have been used to separate the hemicellulose from the biomass, as well as summarizing the most useful pathways that have been used to change the hydrophilic character of hemicelluloses, thus increasing its water resistance and the applications of the targeted water-resistant hemicellulose.


Rohi, M., Ramezani, O., Rahmaninia, M., Zabihzadeh, S. M., and Hubbe, M. A. (2016). “Influence of pulp suspension pH on the performance of chitosan as a strength agent for hardwood CMP paper,” Cellulose Chem. Technol. 50(7-8), 873-878.

Chitosan - a well-known carbohydrate - has found new applications in the papermaking industry. Although the effect of pH on the properties of chemical pulps has been investigated in a number of studies, it has not been reported related to hardwood mechanical pulp, to our knowledge. In the present research, the effect of different pH levels (5.5, 7 and 8.5) on the performance of chitosan as a dry strength additive in paper produced from chemi-mechanical hardwood pulp was studied. The results indicated that the effect of chitosan on the properties of chemi-mechanical paper depended strongly on the pH of the furnish. The addition of chitosan to the stock at acidic pH did not have any specific effect on the strength properties. In contrast, neutral and alkaline pH resulted in improvements in the dry strength properties of paper sheets. The maximum apparent density was observed at pH 8.5, which was attributed to the precipitation of the chitosan on the fiber surface. The results showed that chitosan would be more effective in low dosages. The dependence of chitosan performance on pH in chemi-mechanical pulp was similar to that reported for chemical pulps.

Bildik, A. E., Hubbe, M. A., and Gurboy, K. B. (2016). “Alkyl ketene dimer (AKD) sizing treatment and charge interactions in recycled paper,” Appita J. 69(4), 331-338.

Alkylketene dimer (AKD) sizing dispersions from two commercial sources, in addition to the corresponding laboratory-produced AKD dispersions, were investigated relative to their usage in a recycled office waste furnish. Two main sets of experiments were carried out. One set involved testing the pulp after AKD treatment, with the evaluation of dewatering rates, retention efficiency, and charge. The other set involved brightness and water resistance properties when AKD was added in making handsheets. There was generally a positive but decreasing incremental effect of the sizing treatments (dispersions or associated cationic polyelectrolytes) with increased levels of addition, on drainage rate and retention efficiency. AKD treatment resulted in increased brightness, which was attributed to increased retention of calcium carbonate and of fluorescent whitening agent in the paper. Less sizing agent was required in the recycled furnish compared to the virgin fibre. Results were consistent with the charged character of the emulsified AKD formulations.

Monfared, M. H. A., Resalati, H., Ghasemian, A., and Hubbe, M. A. (2016). “Passivation of pressure sensitive adhesive stickies by addition of acrylic fibers to OCC pulp before papermaking,” Tappi J. 15(10), 631-639.

This study investigated the addition of acrylic fiber to Old Corrugated Container (OCC) pulp as a possible means of overcoming adverse effects of water-based pressure sensitive adhesives during manufacture of paper or paperboard.  Such adhesives can constitute a main source of stickies, which hurt the efficiency of the papermaking process and make tacky spots in the product. The highest amount of acrylic fiber added to recycle pulps generally resulted in a 77% reduction in accepted pulp microstickies. The addition of acrylic fibres also increased pulp freeness, tear index, burst strength, and breaking length, though there was a reduction in screen yield. Hence, in addition to controlling the adverse effects of stickies, the addition of acrylic fibers resulted in the improvement of the mechanical properties of paper compared with a control sample.

Lenze, C. J., Peksa, C. A., Sun, W. M., Hoeger, I. C., Salas, C., and Hubbe, M. A. (2016). “Intact and broken cellulose nanocrystals as model nanoparticles to promote dewatering and fine-particle retention during papermaking,” Cellulose 23(6), 3951-3962. DOI: 10.1007/s10570-016-1077-9

Cellulose nanocrystals (CNCs), either in intact form or after mechanical shortening, were used as a model nanoparticle for enhancement of dewatering and fine-particle retention during lab-scale papermaking process evaluations.  Cryo-crushing, using dry or wet CNCs, was performed to shorten the particles from an initial mean value of 103.1 nm to either 80.4 nm (wet crushed) or 63.4 nm (dry crushed).  Papermaking-related tests were performed with the solids from 100% recycled copy paper, which were prepared as a 0.5% solids suspension in dilute Na2SO4 solution and then treated successively with 0.05% of poly-diallyldimethylammonium chloride, 0.05% of very-high-mass cationic acrylamide copolymer, and then various types and dosages of negatively charged nanoparticles.  The performance of the CNCs, relative to papermaking goals, was compared to that of two colloidal silica products that are widely used in industry for this purpose.  All of the nanoparticles were observed to promote both dewatering and fine-particle retention.  The intact CNCs were more effective than the broken CNCs with respect to fine-particle retention.  Effects on flocculation of the fiber suspension were detectable, but not large relative to the sensitivity of the test employed.  Results are discussed in the light of concepts of polyelectrolyte bridges and the participation of elongated nanoparticles in completing those bridges in such a way as to form shear-sensitive attachments among solids surfaces in the suspension.

Ferrer, A., Pal, L., and Hubbe, M. A. (2016). “Nanocellulose in packaging: Advances in barrier layer technologies,” Industrial Crops and Products 95, 574-582. DOI: 10.1016/j.indcrop.2016.11.012

The review aims at reporting on recent developments in nanocellulose-based materials and their applications in packaging with special focus on oxygen and water vapor barrier characteristics. Nanocellulose materials, including cellulose nanocrystals (CNC), nanofibrillated cellulose (NFC), and bacterial nanocellulose (BNC), have unique properties with the potential to dramatically impact many commercial markets including packaging. In addition to being derived from a renewable resource that is both biodegradable and non-toxic, nanocellulose exhibits extremely high surface area and crystallinity and has tunable surface chemistry. These features give nanocellulose materials great potential to sustainably enhance oxygen and water vapor barrier properties when used as coating, fillers in composites and as self-standing thin films.

Bildik, A. E., Hubbe, M. A., and Gurboy, K B. (2016). “Alkyl ketene dimer (AKD) sizing of paper under simplified treatment conditions,” Tappi J. 15(8), 545-552.

Alkyl Ketene Dimer (AKD) has been widely used by manufacturers of paper and paperboard as a hydrophobic sizing agent. Ordinary sizing with AKD involves a complex series of processes, including emulsification of the waxy AKD material, measures to avoid the agglomeration of the emulsified AKD particles, addition of a stabilized AKD dispersion to papermaking furnish, interactions with various retention aid chemicals to fix the material onto solid surfaces, and various spreading and curing processes that take place during the drying and cooling of the paper product. In the present work, as a means to gain insight into the mechanisms attributable to just the AKD in isolation from the other additives and sub-processes, the AKD wax was dissolved in heptane and applied to filter paper between two aluminum foil layers, followed by evaporation of the solvent and optional heating. Surprisingly, hydrophobic character was obtained regardless of whether or not the treated sheets had been heat-cured. Also, for the first time it was observed that the AKD treatment resulted in a substantial increase in sheet strength, suggesting that the AKD was able to serve as the matrix in an AKD-saturated paper structure. The results add support to past suggestions in the literature that potential covalent interactions cannot account for all of the effects attributable to AKD treatment of paper.

Hubbe, M. A. (2016). “Catalysts inspired by life,” Biofuel Res. J. 11, 430-430.

Biosynthetic processes take place throughout our world with astonishingly high precision and rapidity to create biological systems, trees, and even such complex products as our own bodies.  Though each of the chemical reactions involved in creating something as complex as a tree is thermodynamically possible, there is nearly zero possibility of creating complex biomaterials without the use of enzymes.  Breaking down those biomaterials is somewhat easier – even fire can accomplish that – but still it is enzymes that make most biodegradation possible throughout the world.  An enzyme acts as a catalyst, accelerating and often helping to direct the path of a reaction that would not otherwise take place fast enough or which might otherwise tend to take a different reaction path from what is needed.

But enzymes are not the only kinds of catalysts.  The present issue of Biofuels Research Journal, for instance, has an article that shows how zeolites can help direct the reactions of vapors of pine wood pyrolysis.  Catalysts made by humans often follow our ancient tradition of alchemy:  selecting or modifying minerals or metal ores in the hopes of obtaining something valuable.  In his book The Alchemy of Air, Thomas Hager describes how the chemical engineer/inventors Fritz Haber and Carl Bosch managed to convert gaseous nitrogen into ammonia.  The key was to use an impure iron wire, along with incredibly high pressure and high temperature.  It is estimated that one-half of the nitrogen atoms presently incorporated into your own body, right now, are a direct result of the Haber-Bosch process.  Yes, nitrogen also can be “fixed” by biological processes, but not at a rate that would support the current human population, and humanity had to discover another catalyst in order to sustain the growth of civilization.

Maybe humanity’s current challenge involves advancing beyond “alchemy” and returning to biology as a main arena for catalysis.  Such an approach is represented by the article dealing with biogenic hydrogen production.  Just as in the case of the inorganic catalysts discovered by Haber and Bosch, it takes a great deal of patience and many unsuccessful attempts in order to come up with high-performing enzymes, which may be regarded as biocatalysts.  Many factors may degrade or inhibit the activity of a catalyst.  As emphasized in the review article “Green biodiesel production,” we can expect catalysts to take center stage as humanity grapples with the challenge of sustainability in this increasingly crowded and often hungry world.  These catalysts will take many forms – from transition metal complexes, to enzymes, to pieces of rusty wire.  But without progress in the field of catalysis there is no way that all of us will be able to survive on this planet.

Hubbe, M. A., Metts, J. R., Hermosilla, D., Blanco, M. A., Yerushalmi, L., Haghighat, F., Lindholm-Lehto, P., Khodaparast, Z., Kamali, M., and Elliott, A. (2016). "Wastewater treatment and reclamation: A review of pulp and paper industry practices and opportunities," BioResources 11(3), 7953-8091.

The pulp and paper (P&P) industry worldwide has achieved substantial progress in treating both process water and wastewater, thus limiting the discharge of pollutants to receiving waters. This review covers a variety of wastewater treatment methods, which provide P&P companies with cost-effective ways to limit the release of biological or chemical oxygen demand, toxicity, solids, color, and other indicators of pollutant load. Conventional wastewater treatment systems, often comprising primary clarification followed by activated sludge processes, have been widely implemented in the P&P industry. Higher levels of pollutant removal can be achieved by supplementary treatments, which can include anaerobic biological stages, advanced oxidation processes, bioreactors, and membrane filtration technologies. Improvements in the performance of wastewater treatment operations often can be achieved by effective measurement technologies and by strategic addition of agents including coagulants, flocculants, filter aids, and optimized fungal or bacterial cultures. In addition, P&P mills can implement upstream process changes, including dissolved-air-flotation (DAF) systems, filtration save-alls, and kidney-like operations to purify process waters, thus reducing the load of pollutants and the volume of effluent being discharged to end-of-pipe wastewater treatment plants.

Hubbe, M. A., and Koukoulas, A. A. (2016). "Wet-laid nonwovens manufacture - Chemical approaches using synthetic and cellulosic fibers," BioResources 11(2), 5500-5552.

Wet-laid forming, which can be regarded as being analogous to conventional papermaking processes but with use of chopped synthetic or staple fibers, continues to draw attention as an advantageous way to prepare advanced nonwoven textile products. This review of the literature considers scientific advances in the field, with emphasis placed on applications involving cellulosic fibers as a significant component of the product. Some primary challenges with respect to wet-laid processing concern the dispersion of the synthetic fibers in aqueous media and methods for avoiding their subsequent entanglement. Both mechanical and chemical strategies have been employed in order to achieve well-formed sheets of high uniformity and binding among the fibers to meet a variety of end-use specifications. The incorporation of cellulosic fibers has been shown to facilitate fiber dispersion and to impart certain beneficial characteristics and properties to wet-laid fabrics. The contrasting attributes of synthetic and cellulosic fibers contribute to some unique challenges during the processing of their mixtures during wet-laid forming.

Hubbe, M. A., and Gill, R. A. (2016). "Fillers for papermaking: A review of their properties, usage practices, and their mechanistic role," BioResources 11(1), 2886-2963.

Issues of cost and product quality have caused papermakers to place increased attention on the use of mineral additives, which are the subject of this review article. Technologists responsible for the production of paper can choose from a broad range of natural and synthetic mineral products, each of which has different characteristic shapes, size distributions, and surface chemical behavior. This article considers methods of characterization, and then discusses the distinguishing features of widely available filler products. The mechanisms by which fillers affect different paper properties is reviewed, as well as procedures for handling fillers in the paper mill and retaining them in the paper. Optical properties of paper and strategies to maintain paper strength at higher filler levels are considered. The goal of this review is to provide background both for engineers working to make their paper products more competitive and for researchers aiming to achieve effects beyond the current state of the art.


Hubbe, M. A. (2015). "Oops, I thought that those books had been deacidified," BioResources 10(4), 6305-6309.

Major libraries have been placing increasing reliance upon non-aqueous mass deacidification in an effort to avoid hydrolytic decomposition of the cellulose during storage of bound volumes. Such decomposition is especially a problem when the printing papers used in manufacture of the books have been prepared under acidic conditions, using aluminum sulfate. But there is reason to doubt that the widely used non-aqueous treatments, in which “alkaline reserve” particles are deposited in the void spaces of the paper, can achieve neutralization of acidity throughout the paper structure under the conditions most commonly used for treatment and storage. Anecdotal evidence suggests that alkaline particles such as CaCO3, MgO, Mg(OH)2, or ZnO can be present for long periods of time adjacent to acidic parts of cellulosic fibers without neutralization of the acidity, especially the acidity within the fibers. If these phenomena can be better understood, then there may be an opportunity to use a high-humidity treatment of certain “deacidified” books in order to achieve more pervasive protection against acid-induced degradation.

Silva, D. J., Park, S. W., Hubbe, M. A., and Rojas, O. J. (2015). “Amphoteric polymers to improve paper dry strength,” J. Chem. Eng. Chem. 1(2), 65-79. DOI: 2446941601022015065

The objective of the present work is to evaluate the application of an amphoteric polymer, with acidic and basic groups on the polymer chain, as a paper dry strength additive. The polymer studied here is random terpolymer of high electrostatic charge density, and high molecular weight. The results of our work showed that the balance between the charge densities of the surface and the polymer structures is an important factor to be considered when using this polymer. The highest paper strength value, measured by tensile index, was found at the polyampholyte’s isoelectric point (ca. pH of 7.3) when the charge of the fiber surface was negative and the polymer structure charge was symmetric. This
observation agrees with our dynamic light scattering results which, demonstrated that at the isoelectric point there was a maximum in association among polyampholyte molecules, leading to a maximum in size of molecular aggregates. When adsorbed on an electrically charged surface, the maximum amount of adsorbed polymer, measured by the shift in resonance frequency in a quartz crystal microgravimetric balance, was observed for the same isoelectric point. Better results for paper dry strength were found when the fiber surface and the polymer structures were oppositely charged or at the isoelectric point of the polymer. Less effective addition strategies were found in the case when the fiber surfaces and the
polymer structures had same sign of charge.

Hubbe, M. A., Gardner, D. J., and Shen, W. (2015). "Contact angles and wettability of cellulosic surfaces: A review of proposed mechanisms and test strategies," BioResources 10(4), 8657-8749.

Contact angle methods are widely used to evaluate the wettability of cellulose-based surfaces and to judge their suitability for different applications. Wettability affects ink receptivity, coating, absorbency, adhesion, and frictional properties. There has been a continuing quest on the part of researchers to quantify the thermodynamic work of adhesion between cellulosic surfaces and various probe liquids and to account for such components of force as the London/van der Waals dispersion force, hydrogen bonding, and acid and base interactions. However, due in part to the rough, porous, and water-swellable nature of cellulosic materials, poor fits between various theories and contact angle data have been observed. Such problems are compounded by inherent weaknesses and challenges of the theoretical approaches that have been employed up to this point. It appears that insufficient consideration has been given to the challenging nature of cellulosic materials from the perspective of attempting to gain accurate information about different contributions to surface free energy. Strong hysteresis effects, with large differences between advancing and receding contact angles, have been overlooked by many researchers in attempting to quantify the work of adhesion. Experimental and conceptual approaches are suggested as potential ways to achieve more reliable and useful results in future wettability studies of cellulosic surfaces.

Hubbe, M. A., Sanchez, M. A., Baosupee, D., and Nazhad, M. (2015). “Breakup of agglomerated clusters of cellulosic fines and CaCO3 particles exposed to hydrodynamic stress,” J. Dispersion Sci. Technol. 37(6), 836-845. DOI: 10.1080/01932691.2015.1065504

The capacity of fine particles to remain clustered together after having been agglomerated with the help of polyelectrolytes plays an important role in papermaking and in the treatment of wastewater.  Tests were carried out with agglomerated suspensions of calcium carbonate and primary cellulosic fines in neutral buffer solution.  Agglomeration was induced either by a high-charge cationic polyelectrolyte ( a coagulant) or by sequential treatment with a coagulant and a very-high-mass anionic acrylamide copolymer (a flocculant).  Particle size analysis, based on diffraction of laser light, showed that the coagulated suspensions were susceptible to being redispersed by application of hydrodynamic shear.  By contrast, flocculated suspensions were only partly broken up by shear.  In a flocculated mixture of CaCO3 and cellulosic fines, only the cellulosic fines could be separated from each other, under the conditions employed.  The intensity of shear proved to be more critical than its duration.  Different flow systems were compared and explained in terms of the relative values and types of hydrodynamic stress experienced by the agglomerated particles in different cases.

Baosupee, D., Massey, A. J., Nazhad, M., and Hubbe, M. A. (2015). “Polyelectrolyte coagulant and flocculant effects on heteroagglomeration of cellulosic fines and CaCO3 particles,” APPITA J. 63(3), 237-245.

Effects of a high-charge cationic polyelectrolyte (a coagulant), a very-high-mass cationic polyelectrolyte (a flocculant), or the combination of a cationic coagulant followed by an anionic flocculant were evaluated relative to the particle size distributions in suspensions of cellulosic fines and CaCO3 particles.  Laser diffraction particle size analysis for the mixed suspension showed the virtual disappearance of signal corresponding to unattached CaCO3 particles upon addition of cationic flocculant.  Charge effects related to the coagulant had less influence on the particle size distribution compared to the polymer bridging effects of the flocculant.  Microscopic images revealed differences in the structure of agglomerates in the polymer-treated systems.  The polymer-induced attachments between CaCO3 and cellulosic fines can be interpreted as an additional stage of heteroagglomeration, supplemental to those attachments that had already been formed between CaCO3 and cellulose surfaces prior to addition of the polyelectrolytes. Resulting structures depended not only on the polyelectrolytes but also on the characteristic shapes of cellulosic fines and the fibrillation of their surfaces.

Hubbe, M. A., Rojas, O. J., and Lucia, L. A. (2015). "Green modification of surface characteristics of cellulosic materials at the molecular or nano scale: A review," BioResources 10(3), 6095-6229.

Many current and potential uses of cellulosic materials depend critically on the character of their surfaces. This review of the scientific literature considers both well-established and emerging strategies to change the outermost surfaces of cellulosic fibers or films not only in terms of chemical composition, but also in terms of outcomes such as wettability, friction, and adhesion. A key goal of surface modification has been to improve the performance of cellulosic fibers in the manufacture of composites through chemistries such as esterification that are enabled by the high density of hydroxyl groups at typical cellulosic surfaces. A wide variety of grafting methods, some developed recently, can be used with plant-derived fibers. The costs and environmental consequences of such treatments must be carefully weighed against the potential to achieve similar performances by approaches that use more sustainable methods and materials and involve less energy and processing steps. There is potential to change the practical performances of many cellulosic materials by heating, by enzymatic treatments, by use of surface-active agents, or by adsorption of polyelectrolytes. The lignin, hemicelluloses, and extractives naturally present in plant-based materials also can be expected to play critical roles in emerging strategies to modify the surfaces characteristics of cellulosic fibers with a minimum of adverse environmental impacts.

Hubbe, M. A. (2015). "What next for wood construction/demolition debris?" BioResources 10(1), 6-9.

Residents in localities throughout the world voluntarily participate in the routine recycling of household wastes, such as paper, metals, and plastics containers.  But when a house in their neighborhood gets built or torn down, most of the debris – including wood waste – gets landfilled.  Such a waste of material suggests that there are opportunities to add value to these under-utilized resources. The great variability, as well as contamination, pose major challenges.  It is recommended that reclaimed wood be primarily used in the manufacture of durable goods, and then whatever is left over be used for energy (or heat) generation.


Hubbe, M. A. (2014). A review of ways to adjust papermaking wet-end chemistry: Manipulation of cellulosic colloidal behavior,” Lignocellulose 3(1), 69-107.

This article reviews various adjustments in chemical additives and process conditions that can be used in the course of papermaking to manipulate either the efficiency of the process or the attributes of the resulting paper.  Published studies show that the effects of certain chemical additives to the fiber suspension can be understood based on the forces of interaction between surfaces, i.e. the colloidal forces.  There are opportunities to use such concepts to optimize the efficiency of retention of fine particles and the rate of water release during papermaking.  It is proposed that – for easier understanding – the papermaking process should be viewed as a series of pairwise interactions, for which the outcomes depend on the ionic charges of surfaces, the hydrophobic or hydrophilic character of those surfaces, the balance of charges of dissolved polyelectrolytes, and conditions of hydrodynamic shear inherent in the unit operations of papermaking. 

Hubbe, M. A. (2014). “Lignocellulosic biodegradation in composting,” in: Composting for Sustainable Agriculture, Maheshwari, D. K. (ed.), Vol. 3 in Sustainable Development and Biodiversity ser., Springer, Heidelberg, Ch. 3, 43-66.

Plant-derived material, i.e. lignocellulosic biomass, makes up a major proportion of the initial mass in a typical composting operation.  Such biomass plays some key roles as the mixture is being converted to prepare a useful soil amendment.  For instance, the lignocellulosic component can provide bulking, can help to balance the C:N elemental composition, and serves as the main source of energy for the bacterial processes that go on during composting.  This chapter reviews recent research helping to clarify these roles and to explain the underlying mechanisms.   Recent studies have highlighted the importance of bacterial communities, as well as the succession in the composition of those communities during the different thermal phases of composting.  Progress also has been made in understanding the flows of heat resulting from metabolism, aeration, and chemical changes in the compost mixture.  Advances have been reported in the chemical analysis of compost, revealing details of chemical transformations occurring during the decomposition and stabilization of compost.  The lignin component in a compostable mixture provides chemical building blocks that give rise to humic acids and other substances that resist further biodegradation and allow mature compost to retain water and bind minerals.  Based on the literature one can conclude that composting, especially when lignocellulosic materials are employed under suitable conditions, is an environmentally responsible, relatively mature technology that can be expected to receive increasing research attention in the future.

Hubbe, M. A., Park, J., and Park, S. (2014). "Cellulosic substrates for removal of pollutants from aqueous systems: A review. Part 4. Dissolved petrochemical compounds," BioResources 9(4), 7782-7925.

Dissolved petroleum-based compounds, e.g. solvents, pesticides, and chemical reagents such as phenolic compounds, can pose significant hazards to the health of humans and ecosystems when they are released to the environment.  This review article considers research progress related to the biosorption and removal of such contaminants from water using cellulose-derived materials.  The fact that cellulosic materials show promise in removing such sparingly soluble materials from water lends support to a hypothesis that lignocellulosic materials can be broad-spectrum adsorbents.  Also, the hydrophobic character and sorption capabilities can be increased through thermal treatment and the preparation of activated carbons.  As shown in many studies, the efficiency of uptake of various petrochemical products from water also can be increased by chemical treatments of the adsorbent.  It appears that more widespread adoption of biosorption as a means of removing petroleum-based products from water has been limited by concerns about the used, loaded biosorbent.  Disposal or regeneration options that need to be considered more in future research include enzymatic and biological treatments, taking advantage of the fact that the biosorbent material is able to collect, immobilize, and concentrate various contaminants in forms that are suited for a number of packed bed or batch-type degradative treatment systems.

Hubbe, M. A. (2014). "Puzzling aspects of the hydrophobic sizing of paper and its inter-fiber bonding ability," BioResources 9(4), 5782-5783.

Internal sizing agents make it possible to prepare water-resistant paper from an aqueous suspension comprising water-loving fibers and an emulsified hydrophobic agent.  Why doesn’t the hydrophobic treatment get in the way of inter-fiber bonding?  The answer appears to involve the order in which nano-scale events happen during the manufacture of paper.  It appears that the inter-fiber bonded areas develop first.  Molecular distribution of the hydrophobic agents appears to happen later, especially during the later stages of evaporative drying.  The topic seems to be crying out for someone to carry out appropriate experiments to shed more light on the mechanism.

Hubbe, M. A. (2014). "Zipping backwards the other way - Yet another unique aspect of cellulose," BioResources 9(3), 3759-3760.

Readers of this journal may be keenly aware of cellulose’s remarkable attributes, such as high stiffness, insolubility in just about everything, resistance to enzymatic attack, dimensional stability in the lengthwise direction, and toughness associated with the alternating crystalline zones and less organized regions.  But it you dissolve cellulose and then allow it to recrystallize, the resulting crystals are at the same time radically different, and yet remarkably similar in most respects to the native form.  Exactly half of the macromolecules in regenerated cellulose have been reversed 180 degrees in their direction.  The behavior of dropped pencils can help explain why this happens.

Zhang, W., Liu, W., Li, H., Hubbe, M. A., Yu, D., Li, G., and Wang, H. (2014). “Improving stability and sizing performance of alkenylsuccinic anhydride (SAS) emulsion by using melamine-modified laponite particles as emulsion stabilizer,” Industrial & Engineering Chemistry Research 53, 12330-12338.

Alkenylsuccinic anhydride (ASA) is commonly applied as oil-in-water (o/w) emulsions in the papermaking industry. Herein Laponite mineral nanoparticles were employed as a stabilizer of the ASA emulsions after being modified with melamine just before emulsion preparation. The emulsion was prepared by homogenizing the mixture of ASA and melamine-modified Laponite aqueous dispersion. The modification of melamine on the Laponite was characterized by infrared spectroscopy and X-ray diffraction, whereas the impacts of the modification on the morphology, wettability and zeta-potential of the Laponite, as well as the interfacial tension between ASA and Laponite aqueous dispersion, were also analyzed. It is found that the adsorption of melamine on Laponite particles neither causes the aggregation nor significantly changes the charge properties of the Laponite particles. However, the adsorption of melamine can significantly increase the wettability of Laponite by the ASA liquid, and adequately lower the apparent interfacial tension between ASA and Laponite aqueous dispersion when the melamine-to-Laponite mass ratio is less than 3%. This results in an improvement in emulsion stability, a reduction in emulsion droplet size and an enhancement in the sizing performance of the ASA emulsion when the emulsion is stabilized by melamine-modified Laponite particles. The ASA emulsion with the smallest droplet size and best sizing performance is produced at a melamine-to-Laponite mass ratio of 3%. By monitoring the variations of the emulsion with time, it is discovered that the modification of Laponite with melamine can restrain the growth of emulsion droplets and the hydrolytic action of ASA substantially, thus decreasing the loss in sizing performance of the ASA emulsion with time. This is particularly important for the wide application of ASA emulsions in the papermaking industry.

Song, X. L., and Hubbe, M. A. (2014). “Cationization of oat b-D glucan as a dry-strength additives for paper,” Tappi J. 13(7), 57-64.

Oat beta-D glucan was treated with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (10%, 20%, 30%, or 50% of beta glucan) to obtain a range of cationic beta-D glucan samples. The derivatization was confirmed by the results of Fourier transform infrared (FTIR) tests and elemental analysis. Addition of 1% cationic beta-D glucan based on the mass of unbleached pine kraft fiber increased burst, tensile, and folding endurance properties of the resulting paper. Similar effects were observed at pH 5 and pH 8.5, showing that the system can be considered robust relative to typical acidic and alkaline papermaking conditions. The strength benefits were also observed in recycled sheets made by reslurrying paper prepared with cationic beta-D glucan, even when the initial drying conditions had been severe. The beneficial results of cationization, which can be explained by a more hydrophilic nature and better retention, hold promise as a means of improving the strength properties of virgin paper. The treatment of the initial paper also can enhance the dry-strength performance when the fibers are recovered and used again.

Tan, H., Liu, W., Yu, D., Li, H., Hubbe, M. A., Gong, B., Zhang, W., and Li, G. (2014). “ASA-in-water emulsions stabilized by laponite nanoparticles modified with tetramethylammonium chloride,” Chem. Eng. Sci. 116, 682-693.

Alkenyl succinic anhydride (ASA) is a widely used paper sizing agent that is applied in the form of oil-in-water (o/w) emulsions in order to impart a water-resistant character to the resulting paper. To obtain stable o/w emulsions of ASA, laponite, a highly hydrophilic synthetic clay, was selected as the stabilizer after it had been modified with tetramethylammonium chloride (TMAC), a quaternary ammonium salt with the shortest possible hydrocarbon groups. It was found that the TMAC moderately neutralized the negative charges of laponite particles, lowered the apparent viscosity, but enhanced the turbidity of laponite aqueous dispersion by enhancing the hydrophobicity of the laponite particles, favoring adsorption of laponite particles on the ASA water interface. Meanwhile, the TMAC significantly decreased the interfacial tension between ASA and water/aqueous laponite dispersion, promoting the formation of an emulsion with small droplets. When the added amount of TMAC reached 1 wt% based on laponite, the as-prepared ASA emulsion had small droplet size, low viscosity and uniform droplet size distribution, and exhibited good creaming/coalescence stability. By using TMAC to modify laponite nanoparticles, the hydrolysis stability and sizing performance of ASA emulsion were also improved.

Hubbe, M. A. (2014). “Prospects for maintaining strength of paper and paperboard products while using less forest resources: A Review,” BioResources 9(1), 1634-1763.

Paper production requires large amounts of cellulosic fiber, whereas the world's forested lands and croplands have a finite capacity to supply such resources. To deal with likely future pressure on forest resources, as well as to hold down costs of materials, publications examined in the preparation of this review suggest that the paper industry will need to implement several concurrent strategies. In particular, the industry can be expected to view recycling as a central part of its activities. Basis weights of various paper-based products can be expected to decrease over the coming decades, and more of the fiber content will be replaced with fillers such as calcium carbonate. Such trends will place intense demands upon chemical-based strategies to enhance the bonding within paper and paperboard. Based on the literature, further progress in reducing the amount of new forest resources used to meet a given set of paper product requirements will require a combined approach, taking into account various fiber attributes, nanostructures, novel concepts in bond formation, and advances in the unit operations of papermaking.

Song, X. L., and Hubbe, M. A. (2014). “Enhancement of paper dry strength by carboxymethylated beta-D-glucan from oat as additive,” Holzforschung 68(3), 257-263.

The hypothesis has been tested that a carboxymethyl hemicellulose improves more effectively the dry strength of papers than a native hemicellulose. To that end, beta-D-glucan from oat was treated with an alkaline ethanolic solution of sodium chloroacetate for different times to obtain a range of carboxymethylated beta-D-glucan (CM-glucan) samples. The derivatization was confirmed by Fourier transform infrared spectroscopy and elemental analysis. The physical properties of paper concerning burst and tensile strength as well as folding endurance were essentially improved if CM-glucan was added to unbleached kraft fiber suspension from pine before papermaking. The effects could be maximized by a proper selection of carboxymethylation time and the amount of CM-glucan added to the suspension. The effect was also beneficial in the case of recycled fibers.

Baosupee, D., Massey, A. J., Nazhad, M., and Hubbe, M. A. (2014). “Heteroagglomeration as a mechanism of retaining CaCO3 particles on the fibrils of cellulosic fines: A study by laser light diffraction and microscopy,” Colloids Surf. A: Physicochem. Eng. Aspects 441, 525-531.

Mutual agglomeration involving contrasting types of particles can be expected to play a major role during the formation of paper. The present work employed laser diffraction particle size analysis, as well as microscopy, to characterize the state of agglomeration between cellulosic fines and precipitated calcium carbonate (PCC) particles. Primary fines from bleached hardwood kraft pulp were compared with fines collected from the same pulp after mechanical refining. Various ratios of cellulose to PCC were studied. Results were consistent with a process of heteroagglomeration occurring mainly between the PCC and slender cellulosic fibrils associated with the cellulosic fine particles. Adhesive attachments were formed between the PCC and cellulosic surfaces in spite of their having the same sign of zeta potential. 

Song, X., and Hubbe, M. A. (2014). “TEMPO-mediated oxidation of oat beta-D-glucan and its influences on paper properties,” Carbohydrate Polymers 99, 617-623.

An enhanced bonding agent for papermaking was prepared by selective oxidation of a hemicellulose-rich byproduct of oat processing, which will be identified here by its primary component, beta-D-glucan. The beta-D-glucan was treated sequentially with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and sodium hypochlorite, or alternatively just with sodium hydroxide. When added to a slurry of unbleached softwood kraft fibers, in combination with an optimal dosage of aluminum sulfate, the oxidized beta-D-glucan yielded greater increases in tensile strength and folding endurance in comparison to untreated beta-D-glucan. NaOH treatment also improved dry-strength performance of the beta-D-glucan, except for folding endurance. The improvements were attributed to increased charge density of the treated polyelectrolytes, leading to better distribution and retention on fibers prior to sheet formation. Modified beta-D-glucan also enhanced the strength of recycled sheets when the treated paper was repulped and formed into recycled paper with no further chemical addition.


Hubbe, M. A. (2013). New horizons for use of cellulose-based materials to adsorb pollutants from aqueous solutions,” Lignocellulose 2(2), 386-411.

This article reviews recent research related to biosorption – the use of plant-derived materials to remove various pollutants from aqueous systems.  Emphasis is placed on biosorption studies dealing with the removal of heavy metal ions, dyes, and spilled oil from water.  Much progress already had been achieve in understanding the factors that affect adsorption capacities, rates of uptake, and possible release back into the water.  It has been shown that the performance of cellulose-based sorbent materials often can be improved by physical of chemical modification of the sorbent.  There is a critical need for research related to strategies for dealing with the adsorbent materials after their use.  In addition to regeneration and re-use of sorbent materials, attention also needs to be paid to the incineration of contaminated sorbents, as well as the biodegradation of sorbent material after uptake of various pollutants.

Peresin, M. S., Zoppe, J. O., Vallejos, M. E., Habibi, Y., Hubbe, M. A., and Rojas, O. J. (2013). “Nano- and microfiber composition reinforced with cellulose nanocrystals,” in: Cellulose Based Composites: New Green Nanomaterials, Hinestroza, J., and Netravali, A. N. (eds.), Wiley-VCH, New York, 77-113.

The integration of reinforcing materials in composites with synthetic polymers has gained increased attention in recent years, especially in the area of nanocomposites. Most of the efforts in this respect have focused on inorganic reinforcing agents and mostly by using the casting method. Recently, the developments based on renewable materials have become increasingly popular because of the need for finding alternatives to nonrenewable fossil carbon resources. Among such materials, readily available cellulose nanocrystals (CNs) have attracted great interest because of their availability, renewability, biodegradability, and excellent mechanical properties. Furthermore, CNs are relatively easy to produce and are much less expensive than most of the particles currently used for reinforcement purposes. An additional advantage of CNs and ‘‘lignocellulosics’’ fillers compared to equivalent inorganics include high specific strength, surface reactivity,
and the option of surface modification to give better compatibility with the matrix materials.

Ayoub, A., Venditti, R. A., Pawlak, J. J., Salam, A., and Hubbe, M. A. (2013). “Novel hemicellulose-chitosan biosorbent for water desalination and heavy metal removal,” ACS Sustainable Chem. Eng. 1(9), 1102-1109.

Hemicellulose material is an abundant and relatively under-utilized polymeric material present in lignocellulosic materials. In this research, an alkaline treatment was applied to pinewood (PW), switchgrass (SG), and coastal bermuda grass (CBG) in order to extract hemicelluloses to subsequently produce a novel biosorbent. Alkaline extraction at 75 degrees C recovered 23% of the biomass as a predominantly hemicellulose material with a number average degree of polymerization of similar to 450. These hemicelluloses were grafted with penetic acid (diethylene triamine pentaacetic acid, DTPA) and were then cross-linked to chitosan. The effects of hemicellulose DTPA concentration, reaction time, and temperature of reaction with chitosan on the resulting salt (sodium chloride, NaCl) uptake and weight loss in saline solutions were determined. A maximum salt uptake for the materials was similar to 0.30 g/g of foam biosorbent. The foam biosorbent was characterized by FT-IR spectra, porosity, and dynamic mechanical analysis. Batch adsorption equilibrium results suggest that the adsorption process for salt follows a second-order kinetic model. The hemicellulose-DTPA-chitosan foam biosorbent had uptakes of 2.90, 0.95, and 1.37 mg/g of Pb2+, Cu2+, and Ni2+ ions, respectively, from aqueous medium at initial concentrations of 5000 PPB at pH 5. The cross-linked hemicellulose DTPA chitosan material has good potential for environmental engineering applications.

Hubbe, M. A., Ayoub, A., Daystar, J. S., Venditti, R. A, and Pawlak, J. J. (2013). Enhanced absorbent products incorporating cellulose and its derivatives: A review,” BioResources 8(4), 6556-6629.

Cellulose and some cellulose derivatives can play vital roles in the enhancement of the performance of absorbent products.  Cellulose itself, in the form of cellulosic fibers or nano-fibers, can provide structure, bulk, water-holding capacity, and channeling of fluids over a wide dimensional range.  Likewise, cellulose derivatives such as carboxymethylcellulose (CMC) have been widely studied as components in superabsorbent polymer (SAP) formulations.  The present review focuses on strategies and mechanisms in which inclusion of cellulose – in its various forms – can enhance either the capacity or the rate of aqueous fluid absorption in various potential applications.

Salas, C., Genzer, J., Lucia, L. A., Hubbe, M. A., and Rojas, O. J. (2013). “Water-wettable polypropylene fibers by facile surface treatment based on soy proteins,” ACS Appl.  Mater. Intefaces 5(14), 6541-6548.

Modification of the wetting behavior of hydrophobic surfaces is essential in a variety of materials, including textiles and membranes that require control of fluid interactions, adhesion, transport processes, sensing, etc. This investigation examines the enhancement of wettability of an important class of textile materials, viz., polypropylene (PP) fibers, by surface adsorption of different proteins from soybeans, including soy flour, isolate,glycinin, and beta-conglycinin. Detailed investigations of soy adsorption from aqueous solution (pH 7.4, 25 degrees C) on polypropylene thin films is carried out using quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). A significant amount of protein adsorbs onto the PP surfaces primarily due to hydrophobic interactions. We establish that adsorption of a cationic surfactant, dioctadecyldimethylammonium bromide (DODA) onto PP surfaces prior to the protein deposition dramatically enhances its adsorption. The adsorption of proteins from native (PBS buffer, pH 7.4, 25 degrees C) and denatured conditions (PBS buffer, pH 7.4, 95 degrees C) onto DODA-treated PP leads to a high coverage of the proteins on the PP surface as confirmed by a significant improvement in water wettability. A shift in the contact angle from 128 degrees to completely wettable surfaces (approximate to 0 degrees) is observed and confirmed by imaging experiments conducted with fluorescence tags. Furthermore, the results from wicking tests indicate that hydrophobic PP nonwovens absorb a significant amount of water after protein treatment, i.e., the PP-modified surfaces become completely hydrophilic.

Salas, C., Rojas, O. J., Lucia, L. A., Hubbe, M. A., and Genzer, J. (2013). “On the surface interactions of proteins with lignin,” ACS Appl. Mater. Interfaces 5(1), 199-206.

Lignins are used often in formulations involving proteins but little is known about the surface interactions between these important biomacromolecules. In this work, we investigate the interactions at the solid-liquid interface of lignin with the two main proteins in soy, glycinin (11S) and beta-conglycinin (7S). The extent of adsorption of 11S and 7S onto lignin films and the degree of hydration of the interfacial layers is quantified via Quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR). Solution ionic strength and protein denaturation (2-mercaptoethanol and urea) critically affect the adsorption process as protein molecules undergo conformational changes and their hydrophobic or hydrophilic amino acid residues interact with the surrounding medium. In general, the adsorption of the undenatured proteins onto lignin is more extensive compared to that of the denatured biomolecules and a large amount of water is coupled to the adsorbed molecules. The reduction in water contact angle after protein adsorption (by similar to 40 degrees and 35 degrees for undenatured 11S and 7S, respectively) is explained by strong nonspecific interactions between soy proteins and lignin.

Hubbe, M. A. (2013). Ten-year Forecast of Disruptive Technologies
in the Pulp and Paper Supply Chain, Smithers-Pira, Leatherhead, UK.

This major study from Smithers Pira identifies and profiles the top 25 disruptive technologies that are likely to impact the global pulp and paper supply chain during the coming years up to 2024.  The goal of the work is to anticipate the direction of technology-driven changes related to the use of cellulosic fibres, with an emphasis on pulp and paper products.

Hubbe, M. A., Rojas, O. J., Fingas, M., and Gupta, B. S. (2013). "Cellulosic substrates for removal of pollutants from aqueous systems: A Review. 3. Spilled oil and emulsified organic liquids," BioResources 8(2), 3038-3097.

Water-insoluble oils, including crude petroleum and a wide variety of refined organic liquids, can cause major problems if spilled or leaked to aqueous environments.  Potential environmental damage may be reduced if the spilled oil is promptly and efficiently removed from the water.  This article reviews research that sheds light on the use of cellulose-based materials as sorbents to mitigate effects of oil spills.  Encouraging results for oil sorption have been reported when using naturally hydrophobic cellulosic fibers such as unprocessed cotton, kapok, or milkweed seed hair.  In addition, a wide assortment of cellulosic materials have been shown to be effective sorbents for hydrocarbon oils, especially in the absence of water, and their performance under water-wet conditions can be enhanced by various pretreatments that render them more hydrophobic.  More research is needed on environmentally friendly systems to handle oil-contaminated sorbents after their use; promising approaches include their re-use after regeneration, anaerobic digestion, and incineration, among others.  Research also is needed to further develop combined response systems in which biosorption is used along with other spill-response measures, including skimming, demulsification, biodegradation, and the use of booms to limit the spreading of oil slicks.


Jin, H. Y., Lucia, L. A., Rojas, O. J., Hubbe, M. A., and Pawlak, J. J. (2012). “Survey of soy protein flour as a novel dry strength agent for papermaking furnishes,” J. Agric. Food Chem. 60(39), 9828-9833.

A series of experiments were conducted on recycled pulp samples for the novel purpose of determining the efficacy of employing soy protein flour to increase the strength of dry paper. Values of short span compression and tensile strength were the prime criteria for comparison based on industrial considerations. Various conditions were considered to uncover effective schemes for applying the soy proteins under industrial-like papermaking conditions including alkaline versus acidic as well as high or low ionic content papermaking conditions. A hybrid system of starch, a dry strength additive currently used in paper furnishes, and soy protein was considered to study the possible existence of any synergistic chemical effects. Results indicated that a 1 part (by mass) soy protein to 3 parts cationic starch hybrid system resulted in the highest strength increase in comparison to solely either the soy protein or the cationic starch as dry strength additives.

Payne, K. C., Jackson, C. D., Aizpurua, C. E., Rojas, O. J., and Hubbe, M. A. (2012). “Oil spills abatement: Factors affecting oil uptake by cellulosic fibers,” Environ. Sci. Technol. 46(14), 7725-7730.

Wood-derived cellulosic fibers prepared in different ways were successfully employed to absorb simulated crude oil, demonstrating their possible use as absorbents in the case of oil spills. When dry fibers were used, the highest sorption capacity (six parts of oil per unit mass of fiber) was shown by bleached softwood kraft fibers, compared to hardwood g bleached kraft and softwood chemithermomechanical pulp(CTMP) fibers. Increased refining of CTMP fibers decreased their oil uptake capacity. When the fibers were soaked in water before exposure to the oil, the ability of the unmodified kraft fibers to sorb oil was markedly reduced, whereas the wet CTMP fibers were generally more effective than the wet kraft fibers. Predeposition of lignin onto the surfaces of the bleached kraft fibers improved their ability to take up oil when wet Superior ability to sorb oil in the wet state was achieved by pretreating the kraft fibers with a hydrophobic sizing agent, alkenylsuccinic anhydride (ASA). Contact angle tests on a model cellulose surface showed that some of the sorption results onto wetted fibers could be attributed to the more hydrophobic nature of the fibers after treatment with either lignin or ASA.

Hubbe, M. A., Sundberg, A., Mocchiutti, P., Ni, Y., and Pelton, R. (2012). Dissolved and colloidal substances (DCS) and the charge demand of papermaking process waters and suspensions: A review,” BioResources 7(4), 6109-6193.

Dissolved and colloidal substances (DCS) in the process waters of paper machine systems can interfere with the retention of fine particles, retard the drainage of water from the wet web, and generally hurt the intended functions of various polyelectrolytes that are added to the process. This review considers publications that have attempted to characterize the nature and effects of different DCS fractions, in addition to some of the ways that paper technologists have attempted to overcome related problems. The consequences of DCS in a paper machine system can be traced to their ability to form complexes with various polyelectrolytes. Such tendencies can be understood based on a relatively strong complexing ability of multivalent materials, depending on the macromolecular size and charge density. Continuing research is needed to more fully understand the different contributions to cationic demand in various paper machine systems and to find more efficient means of dealing with DCS.

Carrillo, C. A., Saloni, D., Lucia, L. A., Hubbe, M. A., and Rojas, O. J. (2012). “Capillary flooding of wood with microemulsions from Winsor I systems,” J. Colloid Interface Sci. 381, 171-179.

A new approach based on microemulsions formulated with at least 85% water and minority components consisting of oil (limonene) and surfactant (anionic and nonionic) is demonstrated for the first time to be effective for flooding wood's complex capillary structure. The formulation of the microemulsion was based on phase behavior scans of Surfactant-Oil-Water systems (SOWs) and the construction of pseudo-ternary diagrams to localize thermodynamically stable one-phase emulsion systems with different composition, salinity and water-to-oil ratios. Wicking and fluid penetration isotherms followed different kinetic regimes and indicated enhanced performance relative to that of the base fluids (water, oil or surfactant solutions). The key properties of microemulsions to effectively penetrate the solid structure are discussed; microemulsion formulation and resultant viscosity are found to have a determining effect in the extent of fluid uptake. The solubilization of cell wall components is observed after microemulsion impregnation. Thus, the microemulsion can be tuned not only to effectively penetrate the void spaces but also to solubilize hydrophobic and hydrophilic components. The concept proposed in this research is expected to open opportunities in fluid sorption in fiber systems for biomass pretreatment, and delivery of hydrophilic or lipophilic moieties in porous, lignocellulosics.

Salas, C., Rojas, O. J., Lucia, L. A., Hubbe, M. A., and Genzer, J. (2012). “Adsorption of glycinin and beta-conglycinin on silica and cellulose: Surface interactions as a function of denaturation, pH, and electrolytes,” Biomacromolecules 13(2), 387-396.

Soybean proteins have found uses in different nonfood applications due to their, interesting properties. We report on the kinetics and extent of adsorption on silica and cellulose surfaces of glycinin and beta-conglycinin, the main proteins present in spy. Quartz crystal microgravimetry (QCM) experiments indicate that soy protein adsorption is strongly affected by changes in the physicochemical environment. The affinity of glycinin and the mass adsorbed on silica and cellulose increases (by ca. 13 and 80%, respectively) with solution ionic strength (as it increases from 0 to 100 mM NaCl) due to screening of electrostatic interactions. In contrast, beta-conglycinin adsorbs on the same substrates to a lower extent and the addition of electrolyte reduces adsorption (by 25 and 57%, respectively). The addition 01 10 mM 2-mercaptoethanol, a denaturing agent, reduces the adsorption of both proteins with a significant effect for glycinin. This observation is explained by the cleavage of disulfide bonds which allows unfolding of the molecules and promotes dissociation into subunits that favors more compact adsorbed layer structures. In addition, adsorption of glycinin onto cellulose decreases with lowering the pH from neutral to pH 3 due to dissociation of the macromolecules, resulting in flatter adsorbed layers. The respective adsorption isotherms fit a Langmuir model and QCM shifts in energy dissipation and frequency reveal multiple step kinetic processes indicative of changes in adlayer structure.

Hubbe, M. A., Beck, K. R., O'Neal, W. G., and Sharma, Y. C. (2012). "Cellulosic substrates for removal of pollutants from aqueous systems: A review. 2. Dyes," BioResources 7(2), 2592-2687.

Dyes used in the coloration of textiles, paper, and other products are highly visible, sometimes toxic, and sometimes resistant to biological breakdown; thus it is important to minimize their release into aqueous environments.  This review article considers how biosorption of dyes onto cellulose-related materials has the potential to address such concerns.  Numerous publications have described how a variety of biomass-derived substrates can be used to absorb different classes of dyestuff from dilute aqueous solutions.  Progress also has been achieved in understanding the thermodynamics, kinetics, and chemical factors that control the uptake of dyes.  Important questions remain to be more fully investigated, such as those involving the full life-cycle of cellulosic substrates that are used for the collection of dyes.  Also, more work needs to be done in order to establish whether biosorption should be implemented as a separate unit operation, or whether it ought to be integrated with other water treatment technologies, including the enzymatic breakdown of chromophores.

Hamzeh, Y., Najafi, S. M. H., Hubbe, M. A., Salehi, K., and Firouzabadi, M. R. D. (2012). “Recycling potential of unbleached and bleached chemical pulps from juvenile and mature wood of Populus deltoids,” Holzforschung 66, 155-161.

The recycling potential of unbleached and bleached pulps of juvenile and mature wood of poplar (namely "eastern cottonwood", Populus deltoides) has been investigated. First, chemical and morphological characteristics of juvenile wood (JW), transition wood, and mature wood (MW) of the trunk were determined. Then, high yield and low yield pulps were produced separately from JW and MW by kraft pulping (KP), followed by bleaching of the low-yield pulp with a DED sequence. The obtained handsheet papers were subjected to five successive drying and rewetting cycles (as recycling simulation), and the properties of the corresponding pulps were characterized. The results show that JW is inferior with respect to chemical and morphological properties and resulted in low-yield KP. The bleached pulp obtained from JW required more bleaching chemical to achieve the brightness targets. The strength losses of pulps resulting from recycling were more significant in the first recycling cycle, and then the loss rate decreased with further cycles. The comparison between different pulps showed that the JW pulps were more susceptible to the effects of recycling than MW pulps.


Spence, K. L., Venditti, R. A., Rojas, O. J., Pawlak, J. J., and Hubbe, M. A. (2011). Water vapor barrier properties of coated and filled microfibrillated cellulose composite films,” BioResources 6(4), 4370-4388.

Microfibrillated celluloses (MFCs) have mechanical properties sufficient for packaging applications but lack water vapor barrier properties in comparison to petroleum-based plastics. These properties can be modified by the use of mineral fillers, added within the film structure, or waxes, as surface coatings. In this investigation it was determined that addition of fillers resulted in films with lower densities but also lower water vapor transmission rates (WVTR). This was hypothesized to be due to decreased water vapor solubility in the films. Associated transport phenomena were analyzed by the Knudsen model for diffusion but due to the limited incorporation of chemical factors in the model and relatively large pore sizes, accurate prediction of pore diameters for filled films was not possible with this model. Modeling the filled-films with Fick's equation, however, takes into account chemical differences, as observed by the calculated tortuosity values. Interestingly, coating with beeswax, paraffin, and cooked starch resulted in MFC films with water vapor transmission rates lower than those for low density polyethylene. These coatings were modeled with a three-layer model which determined that coatings were more effective in reducing WVTR.

Hubbe, M. A., Wu, N., Rojas, O. J., and Park, S. (2011). “Permeation of a cationic polyelectrolyte into mesoporous silica. Part 3. Using adsorption isotherms to elucidate streaming potential results,” Colloids Surf. A 381(1-3), 1-6.

Parts 1 and 2 of this series showed that the streaming potential of silica gel particles in aqueous media can be profoundly affected by their exposure to solutions of a cationic polyelectrolyte. The extent of the change in streaming potential depended on such variables as pH, salt concentration, polyelectrolyte molecular mass and concentration, pore size, and time. However, questions arose concerning the relationship between the observed changes in streaming potential and the net amount of adsorbed polyelectrolyte. Some preliminary experiments suggested that, compared to adsorption tests, the streaming potential method may be much more sensitive to the permeation of minor amounts of oligomeric impurities into the network of mesopores in the substrate. The present article follows up on these findings, evaluating adsorption isotherms for the same systems that earlier had been examined by the streaming potential method. In contrast to the earlier work, it was possible to interpret the isotherms based on a model in which adsorbate interacts with a set of equivalent, non-interacting adsorption sites. The kinetics of adsorption were time-dependent and diffusion limited. The polymer adsorbed amount was controlled by both the pore size and the surface area. The highest adsorption amount, based on mass of the substrate, was achieved when using silica gel having an intermediate pore size (15 nm) at a relatively high solution concentration of very-low-mass polyelectrolyte. The results could be fit well to a Langmuir model of the adsorption process.

Silva, D. J., Rojas, O. J., Hubbe, M. A., and Park, S. W. (2011). “Enzymatic treatment as a pre-step to remove cellulose films from sensors,” Macromol. Symp. 299/300, 107-112.

In this work an enzymatic treatment is proposed as a preparative, cleaning protocol to remove cellulose films from resonators and sensors. Quartz crystal and surface plasmon gold sensors, coated with ultrathin films of cellulose are used in studies of molecular (for example, polymer and surfactant) adsorption. The sensors are usually recycled after removal of the film, with limited success, after one of two treatments, either hot acid or ammoniac solutions. In the proposed, improved protocol a mixture of cellulases from Aspergillus species, are used as a pre-treatment to facilitate the release of the cellulose film from the surfaces of the sensors. Two concentrations of NaCl solutions were considered in the enzymatic treatment, 1 and 10 mM, at given enzyme solution concentration, temperature and pH. It was found that after 80 min, the water contact angle after treatment with both salt concentration conditions reached a plateau. The average water contact angle after integration of the enzymatic and ammoniac treatments was found to be low enough, between 6.4 and 7.1 deg to allow reuse the sensors. It is concluded that the use of the ammoniac cleaning solution after the enzymatic treatment is a very convenient, safe and less time consuming way to remove the cellulose films from the sensors to be recycled.

Hubbe, M. A., Hasan, S. H., and Ducoste, J. J. (2011). "Cellulosic substrates for removal of pollutants from aqueous systems: A review. 1. Metals," BioResources 6(2), 2161-2287.

Recent years have seen explosive growth in research concerning the use of cellulosic materials, either in their as-recieved state or as modified products, for the removal of heavy metal ions from dilute aqueous solutions. Despite highly promising reports of progress in this area, important questions remain. For instance, it has not been clearly established whether knowledge about the composition and structure of the bioadsorbent raw material is equally important to its availability at its point of use. Various physical and chemical modifications of biomass have been shown to boost the ability of the cellulose-based material to bind various metal ions. Systems of data analysis and mechanistic models are described. There is a continuing need to explain the mechanisms of these approaches and to determine the most effective treatments. Finally, the article probes areas where more research is urgently needed.  For example, life cycle analysis studies are needed, comparing the use of renewable biosorbents vs. conventional means of removing toxic metal ions from water.  


Hubbe, M. A. (2010). “Using cellulosic materials to remove heavy metals from water,” Research Progress in Paper Industry and Biorefinery (4th ISETPP), S. China Univ. Technol., Nov. 8-10, 1078-1082.

Literature related to bioremediation of toxic metal ions from aqueous solution, using various cellulose-based resources and products, is briefly reviewed.  Studies have proven the effectiveness of a very wide range of cellulosic materials, including wood powder, cellulosic fibers, plant materials, and biomass from bacteria and fungi in removing lead, cadmium, chromium, and many other ions.  Sorptive capacities often can be enhanced by chemical treatment, derivatization, of by pyrolysis to form activated carbon products.  Though the words “ion exchange” are often used to describe the mechanism of uptake, it is clear that chemical complexation – offering a degree of metal-selectivity – is often involved.  Bioeremediation offers a way for cellulose-based industries to contribute to cleaning up aqueous environments.

Hubbe, M. A., Nazhad, M., and Sánchez, C. (2010). "Composting as a way to convert cellulosic biomass and organic waste into high-value soil amendments: A review," BioResources 5(4), 2808-2854.

Plant-derived cellulosic materials play a critical role when organic wastes are composted to produce a beneficial amendment for topsoil. This review article considers publications dealing with the science of composting, emphasizing ways in which the cellulosic and lignin components of the composted material influence both the process and the product. Cellulose has been described as a main source of energy to drive the biological transformations and the consequent temperature rise and chemical changes that are associated with composting. Lignin can be viewed as a main starting material for the formation of humus, the recalcitrant organic matter that provides the water-holding, ion exchange, and bulking capabilities that can contribute greatly to soil health and productivity. Lignocellulosic materials also contribute to air permeability, bulking, and water retention during the composting process. Critical variables for successful composting include the ratio of carbon to nitrogen, the nature of the cellulosic component, particle size, bed size and format, moisture, pH, aeration, temperature, and time. Composting can help to address solid waste problems and provides a sustainable way to enhance soil fertility.

Baty, J. W., Maitland, C. L., Minter, W., Hubbe, M. A., and Jordan-Mowery, S. K. (2010). "Deacidification for the conservation and preservation of paper-based works: A review," BioResources 5(3), 1955-2023.

Embrittlement threatens the useful lifetime of books, maps, manuscripts, and works of art on paper during storage, circulation, and display in libraries, museums, and archives. Past studies have traced much of the embrittlement to the Bronsted-acidic conditions under which printing papers have been made, especially during the period between the mid 1800s to about 1990. This article reviews measures that conservators and collection managers have taken to reduce the acidity of books and other paper-based materials, thereby decreasing the rates of acid-catalyzed hydrolysis and other changes leading to embrittlement. Technical challenges include the selection of an alkaline additive, selecting and implementing a way to distribute this alkaline substance uniformly in the sheet and bound volumes, avoiding excessively high pH conditions, minimizing the rate of loss of physical properties such as resistance to folding, and avoiding any conditions that cause evident damage to the documents one is trying to preserve. Developers have achieved considerable progress, and modern librarians and researchers have many procedures from which to choose as a starting point for further developments.

Hubbe, M. A., Wu, N., Rojas, O. J., and Park, S. (2010). “Permeation of a cationic polyelectrolyte into mesoporous silica. Part 2. Effects of time and pore size on streaming potential,” Colloids and Surfaces A 364(1-3), 7-15.

Streaming potential tests were carried out to determine effects of time and pore size in the adsorption and desorption from aqueous suspensions of cationic polyelectrolytes on silica gel particles. Results in Part 1 of this series showed that the adsorption of cationic polyelectrolytes exposed to mesoporous silica gels can be highly dependent on pH, the polyelectrolyte's molecular mass, and the solution's electrical conductivity. Also, the observed changes in streaming potential indicated that the adsorption tended to be relatively slow and incomplete under the conditions of analysis. The present results indicate that the rate of change of streaming potential is proportional to the logarithm of exposure time. The related changes in adsorbed amounts of polyelectrolyte were below the detection limits of typical polyelectrolyte titration procedures. Contrasting charge behaviors were observed on the exterior vs. interior surfaces of silica gel particles as a function of pore size, electrical conductivity, and polyelectrolyte molecular mass. Increasing ionic strength tended to enhance the effect of adsorption of high-mass cationic polymers on the outer surfaces, but produced only a relatively small effect on streaming potential related to their permeation into silica gel (nominal pore sizes of 6 nm or 30 nm). Adsorption of very-low-mass cationic polymer onto the outer surfaces and inside the 6 nm pore size silica gel appeared to be maximized at an intermediate salt level. Finally, electrokinetic tests were used for the first time in a protocol designed to provide evidence of polyelectrolyte desorption from the interiors of mesoporous materials. 

Kim, G.-Y., and Hubbe, M. A. (2010). “Engineering of a wet-end additives program relative to process parameters and to the physical and optical properties of filled paper,” Indus. Eng. Chem. Res. 49(12), 5644-5653.

In the manufacture of a paper product, the application of wet-end additives and the adjustments of various conditions can have major effects on the physical and optical properties of the final paper. In this study, we prepared paper handsheets and investigated the effects of many process variables, including the type and amounts of cationic polyacrylamide and colloidal silica, in addition to temperature, duration of mixing, hydrodynamic shear, pH, and variations in electrical conductivity due to salt addition. The most important effects were attributable to variations in the amount, ionic charge, and molecular weight of cationic polyacrylamide, as well as the type and amount of colloidal silica. Many of the observed effects could be explained in terms of fiber flocculation, and the adverse effect of flocculation on the uniformity of the paper, a factor that significantly affected the physical properties. An understanding of the relationships between chemical variables, hydrodynamic shear, and other system variables can be helpful in selecting optimal operating conditions to meet process requirements as well as physical properties of the resulting paper. A statistical analysis was carried out, using normalized coordinates, to show which of the independent variables had significant effects on the response variables.

Hubbe, M. A. (2010). “Factors to consider for enhancing and extending the recyclability of paper,”O Papel 71(4), 40-60.

“Saving a valuable resource – fibers” is the reason that many people give when asked why it is good
to recycle paper. But the quality and cost of fibers that can be obtained from post-consumer waste
paper depends to a critical extent on how it was manufactured and converted. The recyclability of
printing paper has been favorably affected in recent decades by the transition to alkaline papermaking
conditions. Conventional dry-strength agents, such as cationic starch, have been found to be very
compatible with recycling. In addition, recent work suggests that the lifetime of kraft fibers can be
prolonged by refining strategies that emphasize external fibrillation and preservation of bulk. But some
other trends are likely to be unfavorable to recycling. There is a danger that some technologies to
remove hemicelluloses prior to pulping will yield fibers that are more susceptible to brittle failure,
especially when they are recycled. Also, high levels of fillers, wax, wet-strength resins, and some
forms of curable inks will continue to pose challenges to paper recycling.

Wu, N., Hubbe, M. A., Rojas, O. J., and Park, S. (2010). “Permeation of a cationic polyelectrolyte into mesoporous silica. Part 1. Factors affecting changes in streaming potential,” Colloids and Surfaces A 364(1-3), 1-6.

A recently developed streaming potential (SP) strategy was used for the first time to investigate factors affecting permeation of the cationic polyelectrolyte poly-(diallyldimethylammonium chloride) from aqueous solution into silica gel particles. Factors affecting cationic polyelectrolyte permeation were considered, including polyelectrolyte dosage, molecular mass, solution pH, and electrical conductivity. Samples were equilibrated for approximately 20 h before testing. The magnitude of change in streaming potential, which was taken as evidence of permeation, increased with increasing polyelectrolyte dosage, with decreasing molecular mass, and with decreasing pH in the range 11 to 3. The pH effect supports a mechanism in which excessively strong electrostatic attraction between the polyelectrolyte and the substrate immobilizes macromolecules at or near the entrances to the pore network, thus inhibiting permeation of like-charged macromolecules. The same mechanism is consistent with observations that permeation increased with increasing electrical conductivity, though the latter observation also could be explained in terms of conformational changes.

Hubbe, M. A. (2010). Ten Year Forecasts of Disruptive Technologies in
Paper and Board to 2020, Pira International.

This major new study from Pira International identifies and profiles the top 25 disruptive technologies that can be expected to affect the global pulp and paper supply chain over the next ten years to 2020. The goal is to anticipate the direction of technology-driven changes related to the usage of cellulosic fibres, with an emphasis on pulp and paper products. 

Song, J., Yamaguchi, T., Silva, D. J., Hubbe, M. A., and Rojas, O. J. (2010). “Effect of charge asymmetry on adsorption and phase separation of polyampholytes on silica and cellulose surfaces,” J. Phys. Chem. B 114(2), 719-727.

The relation between the properties of polyampholytes in aqueous solution and their adsorption behaviors on
silica and cellulose surfaces was investigated. Four polyampholytes carrying different charge densities but
with the same nominal ratio of positive to negative segments and two structurally similar polyelectrolytes (a
polyacid and a polybase) were investigated by using quartz crystal microgravimetry using silica-coated and
cellulose-coated quartz resonators. Time-resolved mass and rigidity (or viscoelasticity) of the adsorbed layer
was determined from the shifts in frequency (Δf) and energy dissipation (ΔD) of the respective resonator.
Therefore, elucidation of the dynamics and extent of adsorption, as well as the conformational changes of the
adsorbed macromolecules, were possible. The charge properties of the solid surface played a crucial role in
the adsorption of the studied polyampholytes, which was explained by the capability of the surface to polarize the polyampholyte at the interface. Under the same experimental conditions, the polyampholytes had a higher nominal charge density phase-separated near the interface, producing a soft, dissipative, and loosely bound layer. In the case of cellulose substrates, where adsorption was limited, electrostatic and polarization effects were concluded to be less significant.

Chen, H., Park, A., Heitmann, J. A., and Hubbe, M. A. (2009). "Importance of cellulosic fines relative to the dewatering rates of fiber suspensions," Ind. Eng. Chem. Res. 48(20), 9106-9112.

When cellulosic fines are present in significant amounts they can have a dominant influence on dewatering. Pulp suspensions drain rapidly if the fines have been removed.  In this study, the dependency of gravity dewatering rates on the level and properties of cellulosic fine matter was quantified.  Bleached hardwood kraft pulp was used as a source of primary fines (collected before refining) and secondary fines (collected after refining of fines-free fiber suspensions).  Fractions of fine matter also were obtained from chemithermomechanical (CTMP) pulp.  Size distributions of these fines were characterized using a laser diffraction method.  Results were explainable by a mechanism in which unattached fines are able to move relative to adjacent fibers during the dewatering and consolidation of a mat of fibers.  Due to such movement, fines end up in locations where they plug drainage channels in the mat.  The contribution of the fines to dewatering increased in inverse proportion to particle size and with increasing surface area, as calculated from the light scattering analysis.

Silva, D. J., Rojas, O. J., Hubbe, M. A., Park, S. W., Yamaguchi, T., and Song, J. (2009). “Polyampholytes: Their use in papermaking and their solution and adsorption behaviors,” O Papel 70(9), 40-50.

A high molecular weight random polyampholyte having both positive and negative charge in the same chain was used in this study as a paper strength additive. Changing the balance between the positive and negative groups in response to different environmental solution conditions was found to affect paper strength properties.   In this research the polyampholyte solution and the adsorption behaviors were studied at a molecular level over a large pH range (4.3 up to 8.5) by using up to date techniques, e.g., quartz crystal microbalance with energy dissipation (QCM-D), atomic force microscopy (AFM) and dynamic light scattering (DLS). The results showed that the polymer structure, morphology and the net charge density of the aggregates at solid-liquid interface affected the adsorbed amount and the viscoelastic layer properties.  A higher amount of adsorbed polymer mass and more viscoelastic layers were found for pH close to the isoelectric point (pHIEP 7.3). In this condition the best paper strength properties were found. Also, we found that this polyampholyte worked very well for recycled fiber application.

Silva, D. J., Rojas, O. J., Park, S. W., and Hubbe, M. A. (2009). “Evaluation of adsorbed polyampholyte layers by using quartz crystal microbalance,” 10th Intl. Symp. Process Systems Engineering – PSE2009, de Brito Alves, R. M., do Nascimento, C. A. O, and Chalbaud Biscaia, E. C., Jr., (eds.).

Viscoelastic properties of layers of polyampholytes adsorbed on charged surfaces were studied by quartz microgravimetry. By applying the Voigt viscoelastic model the effective mass and thickness of layers after adsorption from solution at different salt concentrations were calculated. The obtained results were compared with the Sauerbrey
equation, which applies to the case of thin, rigid adsorbed layers. The estimates of mass and thickness from the Voigt model were typically larger, and were more strongly affected by variations in the ionic strength of adsorbing solution. Since the Voigt model uses multiple frequencies and dissipation overtones, it was found that the calculated
adsorbed layer mass was closer to the actual values, while the Sauerbrey approach resulted in underestimation. This observation was explained by the fact that adsorbed layers of polyampholytes were soft and highly dissipative. It was noted that the observed changes in dissipation of the adsorbed polyampholyte layers were comparatively large, which suggests a large amount of coupled water.

Hubbe, M. A., Nanko, H., and McNeal, M. R. (2009). Retention aid polymer interactions with cellulosic surfaces and suspensions: A Review,” BioResources 4(2), 850-906.

Retention aids can be defined as very-high-mass, water-soluble polymers that are added to cellulosic fiber slurries before the formation of paper in order to improve the efficiency with which fine particles, including cellulosic fines, are retained in the paper product.  Optimization of retention aid performance can be a key to achieving efficient and environmentally responsible papermaking objectives. This article reviews various published theories related to retention aid use.  Findings related to three main classes of retention aid polymers are considered: cationic acrylamide copolymers (cPAM), anionic acrylamide copolymers (aPAM), and polyethylene oxide (PEO).  While many aspects of the interactions of each of these classes of retention aid products can be understood based on colloid chemistry principles, further research is needed in order to more fully bridge the gap between theory and practice.

Hubbe, M. A., and King, K. (2009). Cost-Saving Strategies in Papermaking Chemistry, TAPPI Press, Atlanta, 237 pp.

The goal of this book is to introduce a variety of strategies for cost savings during the manufacture of paper.  Our focus will be on strategies that involve chemical additives.  Chemicals cost money.  It is possible to achieve savings by prudent and well optimized use of additives.  The target audience for this handbook includes two groups:  1) those who will read the book on their own, and 2) those who are fortunate enough to participate in a course.  As members of the papermaking community we are proud to uphold a TAPPI tradition of providing technical books.  Books are a time-proven medium for dissemination of helpful information, allowing the reader to study the material at a self-selected rate, while providing the opportunity to skip directly to the subject matter of most interest and importance.  Readers of this handbook should include engineers, scientists, paper mill staff, chemical company technical support representatives, students, and people from other disciplines who are interested in promoting the economic success of papermaking operations. 

Lee, S. Y., and Hubbe, M. A. (2009). “Morphologies of synthetic mineral microparticles for papermaking as a function of synthetic conditions,” Colloids Surf. A 339(1-3), 118-125.

Morphological characteristics were determined for a system of Synthetic Mineral Microparticles (SMM), which have been developed to promote drainage of water and retention of fine particles during papermaking. Prior research, as well as our own preliminary research showed that the SMM system can have advantages in both of drainage and retention, compared with montmorillonite (bentonite), which is one of the most popular materials presently used in this kind of application. A partially gelled form of a silica-type microparticle additive is known to perform better than the corresponding sol form, in terms of fine-particle retention during papermaking. For this reason it was of interest to investigate the morphological behavior of SMM as a function of the conditions of synthesis. BET nitrogen adsorption was used to measure the surface area of SMM. The distribution of SMM particle size was investigated in the aqueous state, using a light-scattering technique. The coagulation behavior and morphology of SMM were analyzed using scanning electron microscopy (SEM). It was found that the structural characteristics of SMM particles could be explained in terms of the effects of ionic charges on colloidal stability of primary particles during formation of the SMM.

Hubbe, M. A., Chen, H., and Heitmann, J. A. (2009). "Permeability reduction phenomena in packed beds, fiber mats, and wet webs of paper exposed to flow of liquids and suspensions: A review," BioResources 4(1), 405-451.

Filter media, including those prepared from cellulosic materials, often suffer from permeability loss during continued use. To help understand such issues, one can take advantage of an extensive body of related research in such fields as industrial filtration, water purification, enhanced oil recovery, chromatography, paper manufacture, and the leaching of pollutants from impoundments. Though the mechanisms that appear to govern permeability-loss phenomena depend a lot on the details of various applications, the published research has revealed a number of common features. In particular, flow through a porous bed or fiber mat can be markedly reduced by deposition of particles or colloidal matter in positions that either block or partially restrict fluid flow.  Progress has been achieved in the development of mechanistic models, as well as the use of such models in numerical simulations to explain various experimental findings.  Further research of this type needs to be applied to cellulosic materials, which tend to be much more elongated in comparison to the bed materials and suspended matter considered most often by most researchers active in research related to permeability loss.

Lee, S. Y., and Hubbe, M. A. (2008). “Application of synthetic mineral microparticles with various metal species,” J. Korea TAPPI 40(5), 1-10.

Hubbe, M. A., and Rojas, O. J. (2008). Colloidal stability and aggregation of lignocellulosic materials in aqueous suspension: A review,” BioResources 3(4), 1419-1491.

Aqueous dispersions of lignocellulosic materials are used in such fields as papermaking, pharmaceuticals, and preparation of cellulose-based composites. The present review article considers published literature dealing with the ability of cellulosic particle dispersions (fiber, fines, nanorods, etc.) to either remain well dispersed or to agglomerate in response to changes in the composition of the supporting electrolyte solution. In many respects, the colloidal stability and coagulation of lignocellulosics can be understood in terms of well-known concepts, including effects due to osmotic pressure arising from overlapping electrostatic double layers at the charged surfaces.  Details of the morphology and surface properties of lignocellulosic materials give rise to a variety of colloidal behaviors that make them unique.  Adjustments in aqueous conditions, including the pH, salt ions (type and valence), polymers (charged or uncharged), and surfactants can be used to control the dispersion stability of cellulose, lignin, or wood-extractive materials to serve a variety of applications.

Hubbe, M. A. (2008). “Accurate charge-related measurements of samples from the wet end: Testing at low electrical conductivity,” Paper Technol. 49(6), 21-26.

Modest changes in testing procedures can improve the trustworthiness of charge-related measurements at the paper machine wet-end.  This article makes the case for implementing such changes broadly within our industry.  Substantial advantages can be achieved by reducing the salt content of samples of wet-end stock, white water, and similar samples before carrying out tests related to charge.  Improved monitoring and control of charge-related quantities in the wet end has the potential to reduce chemical costs and make the paper machine run more uniformly and efficiently. This paper provides modifications to streaming current (SC) titration procedures and fiber pad streaming potential (SP) procedures.  The SC method is most often used for cationic demand titration endpoint determination, both in the lab and when using online monitoring equipment.  The fiber-pad SP method is most often used for estimating the zeta potential of fiber surfaces, especially for product development and for troubleshooting.

Lee, S. Y., and Hubbe, M. A. (2008). “Polyelectrolyte titrations of synthetic mineral microparticle suspensions to evaluate charge characteristics,” Colloids and Surfaces A 311(3), 175-182.

Colloidal charge properties were determined for a system of Synthetic Mineral Microparticles (SMM), which have been developed to promote drainage of water and retention of fine particles during papermaking. Prior research, as well as our own preliminary research showed that the SMM system can have advantages in both of drainage and retention, compared with montmorillonite (bentonite), which is one of the most popular materials presently used in this kind of application. Streaming current titrations employing highly charged polyelectrolytes and were used to evaluate the charge properties of SMM suspensions and to understand the interactions among SMM particles, fibers, fiber fines, and cationic polyacrylamide (cPAM). Polyelectrolyte titrations were carried out under different conditions of pH to predict the charge properties of SMM under conditions that reflect paper manufacturing practices. It was found that pH variation, caused by the change of Al/Si ratio and partial neutralization of aluminum’s acidity, profoundly affected the charge properties of SMM, due to the variation of Al-ions and the influence ionizable groups on the Si-containing particle surface.

Hubbe, M. A., Heitmann, J. A., and Cole, C. A. (2008).  “Water release from fractionated stock suspensions.  2.  Effects of consistency, flocculants, shear, and order of mixing,” TAPPI J. 7(8), 14-19.

The rate of gravity drainage from a papermaking stock suspension was found to be highly dependent on the initial consistency, as well as on the presence of cellulosic fines.  The results of testing were fitted to a model based on different linear contributions to drainage resistance due to the fibers and due to each type of fines.  Deviations from the model at relatively high consistency were tentatively attributed to flocculation phenomena.  By selectively treating either the fines, the fibers, or the combined furnish with cationic polyelectrolytes it was possible to achieve substantially higher rates of dewatering.  Results were consistent with several mechanisms, which may possibly act in parallel during ordinary papermaking.  Attachment of cellulosic fines to fiber surfaces can prevent those fines from migrating to choke points within a wet web.  Agglomeration of fines to each other can reduce their effective surface area.  Flocculation of the fibers can make the fiber mat less uniform, thus providing larger channels for water to flow from the mat.

Cole, C. A., Hubbe, M. A., and Heitmann, J. A. (2008). “Water release from fractionated stock suspensions.  1.  Effects of the amounts and types of fiber fines,” TAPPI J. 7(7), 28-32.

Tests with a gravity-based freeness device demonstrated a highly non-linear effect of cellulosic fines on resistance to dewatering.  Fines at low to moderate levels had little effect on gravity dewatering, but fines slowed drainage considerably as their level increased beyond a threshold.  Fines created by refining (secondary fines) slowed drainage to a much greater extent than those originally present in bleached hardwood kraft pulp (primary fines).  The results were consistent with a mechanism in which unattached fines can migrate within a wet web to choke points at which they tend to block the flow of water. 

Hamzeh, Y., Ekhtera, M. H., Hubbe, M. A., Izadyar, S., and Pourtahmasi, K. (2008), “Effects of process variables on poly-aluminum chloride (PAC)-rosin sizing performance under neutral papermaking conditions,” Industrial and Engineering Chemistry Research 47, 4302-4307.

The effects of process variables, including poly-aluminum chloride (PAC) and rosin levels and equilibration
time on PAC-rosin sizing performance, were investigated for three alternative sizing processes, include
conventional, reverse sizing, and premixing under neutral papermaking conditions. The individual and
interaction effects of sizing variables were determined. It was found that, in contrast to conventional sizing,
the sizing efficiency increased with increasing equilibration time when reverse and premixing processes were
used for the sizing treatment. In both processes, increasing equilibration time can lead to potential savings in
PAC or rosin. Finally, the optimum conditions for more cost-effective sizing were determined for the three
sizing processes.

Bastidas, J. C., Pawlak, J. J., Venditti, R. A., Heitmann, J. A., Hubbe, M. A., and Kadla, J. F. (2008). “A colloidal probe microscopy study of cellulose/gypsum interactions,” Materials Characterization 59(2), 144-150.

Drywall, which is made primarily of a calcium sulfate dihydrate (gypsum) core with paper on both sides, is one of the most widely used construction materials. Because board failure often occurs at the gypsum core/paper interface, it has become important to know the exact nature of the gypsum/cellulose bond. This study provides data about the nature of this interaction by means of AFM and Colloidal Probe Microscopy. These methods made it possible to distinguish among the different crystal faces and their respective interactions with cellulose. Measured in air, the adhesive forces between the AFM tip and the different faces varied according to f(010) < f(120) < f(111) at 50 % relative humidity. The differences in adhesive force with the different gypsum crystals can be attributed to the differences in surface chemistry. The information obtained will help guide improvements in the crystal production process to obtain better bonding between the crystal and the paper.
Hubbe, M. A. (2008). “Minimizing the environmental impact of the papermaking process,” Proceedings of the 2nd IPEC Conference, Tianjin, China, Book A, 37-40.

From an environmental perspective, papermakers have a positive story to tell. The products that we manufacture mainly come from renewable resources. Paper can be recycled. It’s also biodegradable. It also can be incinerated to recover its energy value. However, the process of making paper also can raise some environmental concerns. Decades ago it was common to be able to see environmental impacts of papermaking additives just by looking at a waterway downstream of a paper mill. The color of river water often was a good clue as to what color of paper was being manufactured. Such impacts have been greatly reduced, not only due to implementation of wastewater treatment operations, but also to advances in papermaking chemistry – making it possible to achieve high levels of retention efficiency. In the future we can expect there to be increasing emphasis on the overall environmental impact of each chemical additive that is used.  Issues that will be considered will include the chemical’s toxicity, biodegradability, and its tendency (or lack thereof) to become retained on solid surfaces. Certain papermaking additives also have the potential to reduce the need for fibers – or to enable the papermaker to meet specifications at higher filler levels or lower basis weights. Further opportunities lie in the area of automation, making it possible to use chemical additives more efficiently. Looking toward the future, perhaps energy use will emerge as the dominant issue. Evaporation of water is the most energy-demanding part of the papermaking process. Though it is very difficult to demonstrate conclusively, some of the same chemicals that can promote faster dewatering in the forming section also appear to make it easier to squeeze water out of paper in the press section, reducing the amount of evaporation required.

Wu, N., Hubbe, M. A., Rojas, O. J., and Yamaguchi, T. (2008). “Penetration of high-charge cationic polymers into silica gel particles and cellulosic fibers,” Proceedings of the 2nd IPEC Conference, Tianjin, China, Book B, 626-649.

The gradual penetration of positively charged polymeric additives below the outer surfaces of cellulosic fibers can play an important role in the selection of addition points and optimization of chemical dosages on a paper machine. The present work was undertaken to help understand the role of high and low-molecular-mass fractions of a cationic polyelectrolyte, in determining the charge behavior of the outer surfaces of fibers. Commercial polyelectrolyte samples typically contain a broad range of molecular masses. A dialysis procedure was used to selectively remove the low-mass fraction of poly-diallyldimethylammonium chloride (poly-DADMAC) from aqueous solutions of the polymer. Only cationic polymer samples having a very-low-mass component exhibited penetration into the interior spaces of silica gel, which has a well-defined, narrow pore size distribution. The presence of low-mass components of the polymer also affected the electrical potential associated with the outer surfaces of solids treated with high-mass poly-DADMAC. Preliminary observations showed related behavior in the case of cellulosic fibers. The wide range of time required for measured streaming potential values to decrease to zero, depending on the amount of poly-DADMAC added at time zero, was consistent with a gradual diffusion of the macromolecules below the outer surfaces of the fibers.

Hubbe, M. A., Rojas, O. J., Lucian, L. A., and Sain, M. (2008). Cellulosic nanocomposites, A review,” BioResources 3(3), 929-980.

Because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties, a great deal of attention has been paid recently to cellulosic nanofibrillar structures as components in nanocomposites. A first major challenge has been to find efficient ways to liberate cellulosic fibrils from different source materials, including wood, agricultural residues, or bacterial cellulose. A second major challenge has involved the lack of compatibility of cellulosic surfaces with a variety of plastic materials. The water-swellable nature of cellulose, especially in its non-crystalline regions, also can be a concern in various composite materials. This review of recent work shows that considerable progress has been achieved in addressing these issues and that there is potential to use cellulosic nano-components in a wide range of high-tech applications.

Hubbe, M. A., Pawlak, J. J., and Koukoulas, A. A. (2008). "Paper's appearance: A review," BioResources 3(2), 627-665.

This review article highlights progress in understanding the optical properties of paper.  Paper’s appearance can be defined in terms of its opacity, brightness, color, fluorescent properties, gloss, and various quantities related to its uniformity.  The phenomena that give rise to paper’s optical properties, especially its ability to scatter and absorb visible light, are highly dependent on paper’s structure and its chemical composition.  In an effort to engineer low-cost products having relative high opacity and brightness, it is necessary to optimize the material selection and processing conditions.  The dimensions of solid materials and void structures within the paper are key factors for optimizing the optical properties.  In addition, additives including bleaching agents, mineral particles, dyes, and fluorescent whitening agents can impact paper’s optical properties  Paper’s appearance depends, in subtle ways, on the processes of its manufacture.

Hubbe, M. A., Venditti, R. A., and Rojas, O. J. (2007). "What happens to cellulosic fibers during papermaking and recycling? A review," BioResources 2(4), 739-788.

Both reversible and irreversible changes take place as cellulosic fibers are manufactured into paper products one or more times.  This review considers both physical and chemical changes.  It is proposed that by understanding these changes one can make better use of cellulosic fibers at various stages of their life cycles, achieving a broad range of paper performance characteristics.  Some of the changes that occur as a result of recycling are inherent to the fibers themselves.  Other changes may result from the presence of various contaminants associated with the fibers as a result of manufacturing processes and uses.  The former category includes an expected loss of swelling ability and decreased wet-flexibility, especially after kraft fibers are dried.  The latter category includes effects of inks, de-inking agents, stickies, and additives used during previous cycles of papermaking.

Hubbe, M. A., Rojas, O. J., Lucia, L. A., and Jung, T. M. (2007). “Consequences of the Nanoporosity of Cellulosic Fibers on their Streaming Potential and their Interactions with Cationic Polyelectrolytes,” Cellulose 14(6), 655-671.

Electrokinetic tests, based on the streaming potential method, were used to elucidate interactions between cationic polyelectrolytes and cellulosic fibers and to reveal aspects of fibers’ nanoporosity.  The fibrillated and nanoporous nature of bleached kraft fibers gave rise to time-dependent changes in streaming potential, following treatment of the wetted fibers with poly-diallyldimethylammonium chloride.  Electrokinetic test results were consistent with an expected longer time required for higher-mass polyelectrolytes to diffuse into pore spaces, compared to lower-mass polyelectrolytes.  Further evidence of the relative inability of polyelectrolyte molecules to diffuse in to the pores of cellulose was obtained by switching back and forth between high and low ionic strength conditions during repeated measurement of streaming potential, after the fibers had been treated with a moderate amount of cationic polymer.  By changing the concentration of sodium sulfate it was possible to switch the sign of streaming potential repeatedly from positive to negative and back again.  Such results imply that a continuous path for liquid flow exists either in a fibrillar layer or within the cell walls.  The same concepts also helped to explain the dosages of high-charge cationic polymer needed to achieve maximum dewatering rates, as well as the results of retention experiments using positively and negatively charged microcrystalline cellulose particles.

Hubbe, M. A. and Panczyk, M. (2007). “Dewatering of refined, bleached hardwood kraft pulp by gravity, vacuum, and centrifugation with applied pressure.  Part 1.  Physical and ionic effects,” O Papel 68(10), 74-87.

Three types of dewatering tests were performed with refined, bleached hardwood kraft suspensions.  A modified water retention value (MWRV) test was used, with pressure applied to damp plugs of fibers during their centrifugation.  Refining levels and drying conditions had dramatic and consistent effects on dewatering rates by gravity (freeness tests), with the application of vacuum, and also the MWRV tests.  Effects of drying were roughly equivalent to a reversal of refining effects.  Though changes in the pH and salt concentration of the aqueous solution had large effects on dewatering by gravity or vacuum, these chemical conditions did not affect MWRV results to a significant extent.

Hubbe, M. A. and Panczyk, M. (2007). “Dewatering of refined, bleached hardwood kraft pulp by gravity, vacuum, and centrifugation with applied pressure.  Part 2.  Effects of wet-end additives,” O Papel 68(10), 88-100.

Several wet-end chemical additives significantly affected dewatering rates according to gravity drainage tests (freeness), the application of vacuum, and a modified water retention value (MWRV) test.  Relatively large increases in dewatering rates, including reductions in MWRV, were obtained by addition of high-charge synthetic cationic polymers to the pulp suspensions.  Results were consistent with charge neutralization and polyelectrolyte complexation within the fibrillated layers of the fiber surfaces.  These mechanisms appear to have caused less water to be held in spaces between the fibers after they had been centrifuged in the presence of applied pressure.  Successive treatment with a cationic acrylamide copolymer (cPAM), followed by colloidal silica, a so-called microparticle program, resulted in very pronounced acceleration of gravity- and vacuum-assisted dewatering.  Though the microparticle system yielded reduced MWRV results under certain conditions, combinations of cPAM and colloidal silica at high levels increased the amount of water retained in compressed fiber pads after centrifugation.

Hubbe, M. A., and Heitmann, J. A. (2007). "Review of factors affecting the release of water from cellulosic fibers during paper manufacture," BioResources 2(3), 500-533.

The ease with which water becomes released from cellulosic fiber material during the manufacturing of paper can affect both the production rate and the consumption of energy during the manufacturing process.  Important theoretical contributions to dewatering phenomena have been based on flow through packed beds of uniformly distributed fibers.  Such descriptions are able to explain why resistance to dewatering increases as a function of the wet surface area of fibers.  More recent studies have demonstrated a critical role of fine matter.  If the fines are unattached to fibers, then they tend to move freely through the fiber mat and plug channels in the paper web during the dewatering process.  Dewatering also is affected by the deformability of cellulosic fibers, and by whether the fibers easily slide past each other, thereby forming a dense mat.  By emphasizing the role of fine matter, colloidal forces, and conformability of cellulosic materials, one can gain a more realistic understanding of strategies that papermakers use to enhance initial drainage and vacuum-induced dewatering.

Hubbe, M. A., Rojas, O. J., Argyropoulos, D. S., Wang, Y., Song, J., Sulic, N., and Sezaki, T., "Charge and the dry-strength performance of polyampholytes. Part 2. Colloidal effects," Colloids and Surfaces. A, Physicochemical and Engineering Aspects 301, 23-32 (2007).

Polyampholytes, which are macromolecules that contain both positive and negative ionizable groups, can provide superior strength improvements for paper manufacture, compared to the addition of simple polyelectrolytes.  Colloidal effects, which were measured in solution and in fiber suspensions, were consistent with observed bonding effects.  The same colloidal effects were found to correlate with the effects of pH and of the density of the ionizable groups on the polyampholytes.  Tests were carried out with a series of polyampholytes having a constant ratio of cationic to anionic monomeric groups and molecular mass.  Their charge density varied in the ratio 1:2:4:8.  The greatest strength gains were obtained at intermediate charge density and under conditions of pH favoring instability of the aqueous polymer mixtures.  Colloidal phenomena were elucidated by turbidimetric tests, sediment volumes of treated fiber suspensions, flocculation tendencies of treated fiber suspensions, and zeta potentials of probe particles.

Wang, Y., Hubbe, M. A., Rojas, O. J., Argyropoulos, D. S., Wang, X., and Sezaki, T. "Charge and the dry-strength performance of polyampholytes. Part 3. Streaming potential analysis," Colloids and Surfaces. A, Physicochemical and Engineering Aspects 301, 33-40 (2007).

Results reported in Part 1 of this series showed that paper strength improvements could be optimized by varying pH and the overall content of ionic groups in random terpolymers containing a fixed molar ratio of acidic and basic monomeric groups.  Further treatment of kraft fiber slurries with polyaluminum chloride (PAC), after polyampholyte addition, yielded significant strength benefits.  The present paper shows how these results can be explained in terms of the streaming potential of glass fibers, which were used as a model substrate.  The data suggest that aluminum ions interact both with the anionic carboxyl groups of the polyampholytes and with anionic silanol groups at fiber surfaces.  The streaming potential of the treated surfaces could be changed by varying the pH, the overall density of charged groups of the polyampholytes, the ratio of cationic to anionic groups on the polymer, and by post-treatment with poly-aluminum chloride.

Hubbe, M. A., Rojas, O. J., Lee, S. Y., Park, S., and Wang, Y. "Distinctive electrokinetic behavior of nanoporous silica particles treated with cationic polyelectrolyte," Colloids and surfaces. A, Physicochemical and Engineering Aspects 292(2-3), 271-278 (2007).

In this study we show, for the first time, that the streaming potential of aqueous suspensions of nanoporous silica gel, after treatment with the cationic polyelectrolyte poly-diallyldimethylammonium chloride (poly-DADMAC), can depend very strongly on the concentration of background electrolyte.  An increase in the electrical conductivity from 60 to 1000 µS/cm resulted in an approximately 1000-fold increase in the amount of poly-DADMAC that was required to reach an endpoint of zero streaming potential.  Results were explained by two contributions to the overall electrokinetic behavior – one due to the outer surfaces and another due to the interior surfaces of nanopore spaces that were inaccessible to the polyelectrolytes.  Experiments with cyclical changes in salt content revealed a high degree of reversibility; such observations help to rule out explanations based on salt-induced desorption or enhancement of pore penetration.  Supplementary tests with non-porous glass fibers showed no evidence of the distinctive electrokinetic behavior observed in the case of nanoporous particles.  Effects of polymer molecular mass and pH, evaluated under similar experimental conditions, agreed with well-established trends. 

Hubbe, M. A., "Flocculation and redispersion of cellulosic fiber suspensions: A review of effects of hydrodynamic shear and polyelectrolytes," BioResources 2(2), 296-331.

Cellulosic fibers in aqueous suspensions are subject to flocculation effects that involve two contrasting scales of dimension. The net effect of flocculation determines how uniformly fibers can become formed into a sheet during the manufacture of paper. At a macroscopic level, the highly elongated shape of typical wood-derived fibers in agitated sus-pensions can give rise to frequent inter-fiber collisions and the formation of fiber flocs. At a submicroscopic scale, surfaces of suspended materials can become joined by macromolecular bridges. Although such bridges tend to reduce paper’s uniformity, polyelectrolyte flocculants are used in most paper machine systems to achieve relatively high retention efficiencies of fine particles as paper is being formed. By adjusting the papermaking equipment, judiciously selecting points of addition of chemicals, and by managing chemical dosages, papermakers employ a variety of strategies to achieve favorable combinations of retention and uniformity. This review considers scholarly work that has been directed towards a greater understanding of the underlying mechanisms.

Hubbe, M. A. "Paper's resistance to wetting: A review of internal sizing chemicals and their effects," BioResources 2(1), 106-145 (2007).

This review considers research related to internal sizing agents.  Such chemicals, when added as emulsions or in micellar form to slurries of cellulosic fibers before paper is made, can make the product resist water and other fluids.  Significant progress has been achieved to elucidate the modes of action of alkylketene dimer (AKD), alkenylsuccinic anhydride (ASA), rosin products, and other sizing chemicals.  Recent findings generally support a traditional view that efficient hydrophobation requires that the sizing chemicals are efficiently retained on fiber surfaces during the papermaking process, that they become well distributed on a molecular scale, and that they need to be chemically anchored.  A variety of studies have quantified ways in which internal sizing treatments tend to be inefficient, compared to what is theoretically possible.  The inefficient nature of chemical and physical processes associated with internal sizing, as well as competing reactions and some interfering or contributing factors, help to explain apparent inconsis-tencies between the results of some recent studies.

Hubbe, M. A., Rojas, O. J., Sulic, N., and Sezaki, T. "Unique behavior of polyampholytes as dry-strength agents," Appita Journal 60(2), 106-111 (2007).

Polyampholytes yielded superior dry strength increases following their addition to slurries of papermaking fibres.  The bi-ionic polymers achieved greater tensile strength, compared to similar polymers having ionic groups of only positive or negative charge.  Dry-strength efficiency increased with increasing charge density of the polyampholyte.  Strength results were consistent with turbidity data, showing that the polyampholytes generally became less soluble at intermediate values of pH.  In contrast to simple polyelectrolytes, the adsorbed amphoteric macromolecules imbibed significant amounts of water of hydration.  Though high levels of polyampholytes added to the furnish tended to reduce the rate of gravity dewatering, such effects tended to be lower than the drainage inhibition caused by single-charge polyelectrolytes.  The effects of polyampholytes were achieved without the adverse effects often associated with refining, e.g. decreased dewatering rates, fibre shortening, or changes in the conformability of the fibres.

Wang, Y., Hubbe, M. A., Sezaki, T., Wang, X. W., Rojas, O. J., & Argyropoulos, D. S. "Aspects of retention and formation - The role of polyampholyte charge density on its interactions with cellulose," Nordic Pulp & Paper Research Journal 21(5), 638-645 (2006).

Polyampholytes offer considerable promise as dry-strength additives, but the molecular mechanism involved in their adsorption needs to be better understood.  Amphoteric terpolymers of acrylamide, itaconic acid, and N-[3-(NN’,N’-dimethylamine)propyl]acrylamide (DMAPAA) with a constant ratio of basic to acidic groups (5:4) were prepared by random polymerization.  The basic groups ranged from 2.5 to 20 mole percent in the terpolymers.  Analysis by 1H and 13C nuclear magnetic resonance revealed near-quantitative agreement with the make up stoichiometry.
Streaming potential tests showed significant effects of polyampholyte adsorption, depending on the charge density of the polyampholyte, its level of addition, the pH, and the background electrolyte.  Polyampholytes having higher density of ionizable groups yielded more positive streaming potential at low pH values and more negative streaming potentials at high pH values, compared to polyampholytes of lower charge density.  At the extremes of pH, e.g. pH=3 and pH=11, the effects of a polyampholyte on streaming potential were similar to those of single-charged polyelectrolytes having a matched degree of substitution of charged monomeric groups.  Except for the sample having the lowest density of charges, all of the polyampholyte samples showed a broad maximum in adsorbed amount vs. pH within the range of about pH=5 to pH=9, which is intermediate between the pKa values of the respective charged groups.

Hubbe, M. A. "Bonding between cellulosic fibers in the absence and presence of dry-strength agents - A review," BioResources 1(2), 281-318 (2006).

Various water-loving polyelectrolytes, including cationic starch products, are used by papermakers to promote inter-fiber bonding and increase paper’s dry-strength.  Thus, papermakers can meet customer require-ments with a lower net cost of materials, more recycled fibers, or higher mineral content.  In the absence of polymeric additives, key mechanisms governing bond development between cellulosic fibers include capillary action, three-dimensional mixing of macromolecules on facing surfaces, conformability of the materials, and hydrogen bonding.  Dry-strength additives need to adsorb efficiently onto fibers, have a water-loving character, and have a sufficiently high molecular mass.  Though it is possible to achieve significant strength gains by optimal usage of individual polymeric agents, greater strength gains can be achieved by sequential addition of oppositely charged polyelectrolytes.  Superior strength can be achieved by in-situ formation of polyelectrolyte complexes, followed by deposition of those complexes onto fiber surfaces.  Polyampholytes also hold promise as efficient dry-strength additives.  Opportunities for further increases in performance of dry-strength agents may involve fiber surface modification, self-assembled layers, and optimization of the dry film characteristics of dry-strength polymers or systems of polymers.

Song, J., Wang, Y., Hubbe, M. A., Rojas, O. J., Sulic, N., & Sezaki, T. "Charge and the dry-strength performance of polyampholytes. Part 1, Handsheet properties and polymer solution viscosity," Journal of Pulp and Paper Science, 32(3), 156-162 (2006).

Paper strength was increased by adding random terpolymers having a fixed ratio of basic to acidic monomeric groups to bleached kraft fiber slurries over a wide range of pH.  Subsequent treatment of the fiber slurries with polyaluminum chloride (PAC) further increased tensile breaking length.  By contrast, PAC tended to reduce the dry strength contribution of a cationic polyelectrolyte having the same mass and cationic monomer content as one of the polyampholytes .  The reason for adding the PAC last to the mixture was to evaluate possible effects of fresh, highly cationic aluminum species with the polymers as well as the fiber surfaces.  It is proposed that such effects are due to the influence of pH and ionic aluminum species on the molecular conformations, as well as the electrokinetic behavior of solids exposed to the polyampholytes.  Results of solution viscosity tests indicated more expanded polyampholyte conformations resulting from PAC addition, especially in those cases where dry strength advantages of PAC addition were observed. 

Heermann, M. L., Welter, S. R., and Hubbe, M. A., "Effects of High Treatment Levels in a Dry-Strength Additive Program Based on Deposition of Polyelectrolyte Complexes: How Much Glue is Too Much?" Tappi J. 5 (6): 9-14 (2006).

Large increases in paper's dry strength were achieved in this study by depositing high levels of polyelectrolyte complexes onto fibers. A previous study, utilizing glass microfibers, showed an almost linear increase in strength with increasing polymer amounts up to 10%, on a dry basis. Such results prompted questions related to the practical upper limits of addition of dry-strength chemicals. Substantial gains in tensile breaking length were achieved in the present work by sequential addition of balanced amounts of positively and negatively charged polymers to bleached kraft fibers. Strength increased strongly with increasing dosages up to 40% net polymer addition. These results contrasted with past work showing that further addition of single-polymer dry-strength additives often becomes ineffective above about 0.2 to 2% addition, in different cases. Efficient retention of the polymers onto the fibers, even up to a level of equal amounts of polymer and fiber, was evident from the basis weight of handsheets prepared from a constant amount of fiber. Practical upper limits of polymer addition for the dual-polymer system were evident from an increasing stickiness of undried paper handsheets, with increasing polymer dosage. Other problems associated with the highest polymer dosages considered included polymer deposition onto the forming fabric, reduced dewatering rates, and reduced opacity of paper produced with 40% or more dry mass of polyelectrolyte added, based on fiber mass. Important factors affecting the results included the ratio of the two kinds of polymers and the manner in which the polyelectrolyte solutions were added.

Sezaki, T., Hubbe, M. A., Heitmann, J. A., and Argyropoulos, D. S. (2006). "Colloidal effects of acrylamide polyampholytes. Part 2, Adsorption onto cellulosic fibers," Colloids and surfaces. A, Physicochemical and engineering aspects, 289(1-3), 89-95.

Colloidal titrations of commercial acrylamide-based terpolymers having both weak-acidic and weak-basic groups were carried out at pH 3 and 11, using a streaming current technique.  At these pH values it was found that the polyampholytes could be considered as simple polyelectrolytes, though it was necessary to use a modified titration procedure.  The titration endpoint defined by zero streaming current (SC) output deviated from a 1:1 stoichiometry, depending on the salt concentration.  The endpoint also depended at the speed of titration, consistent with a relatively slow rate of forming equilibrated poly-ion complexes between polyampholytes and titrants.  The adsorption of the amphoteric polyacrylamide copolymers onto bleached hardwood fibers was maximized near to its isoelectric pH, such that the net charge of the polymer was relatively low, but opposite to that of the substrate.  Neutral and negatively charged polyampholytes also adsorbed in significant amounts onto the negatively charged fibers, though the amounts were lower than when the net charges were opposite.  Addition of salt generally increased adsorption up to a conductivity value of 1000 mS/cm.  Adsorption increased slightly with increasing time, until reaching a plateau.  The rate of fluid agitation during adsorption did not affect adsorption significantly under the conditions employed. 

Sezaki, T., Hubbe, M. A., Hietmann, J. A., Argyropoulos, D. S., and Wang, X., "Colloidal Effects of Acrylamide Polyampholytes. Part 1. Electrokinetic Behavior," Colloids Surf. A, 281 (1-3), 74-81 (2006).

The colloidal and electrokinetic behavior of three amphoteric acrylamide-based water-soluble terpolymers of high molecular mass was elucidated in terms of their structure and composition, using potentiometric and colloidal titrations, as well as microelectrophoresis, viscometry, and turbidity measurements. Independent variables included polymer composition, pH, and the concentration of salt ions. The electrokinetic properties, titratable charge, and isoelectric pH values of the samples were compared to their monomeric composition, as confirmed by NMR and FTIR analysis. The electrophoretic mobilities of the polyampholytes changed relatively rapidly with pH in the neighborhood of the isoelectric pH values, consistent with an enrichment of excess charges toward the outer parts of the macromolecules. Interactions of the polyampholytes with highly-charged titrants appeared to be less pH-dependent, in the neighborhood of the isoelectric condition, relative to a linear prediction based on the numbers of acidic and basic macromolecular groups. Specific viscosity measurements, in the vicinity of the isoelectric point, were found to increase with increasing salt concentration, which is a typical anti-polyelectrolyte behavior. In a similar manner, salt addition suppressed the development of a turbidity maximum at the isoelectric point.

Hubbe, M. A., Rojas, O. J., and Venditti, R. A., "Control of Tacky Deposits on Paper Machines - A Review," Nordic Pulp Paper Res. J. 21 (2), 154-171 (2006).

Wood-derived pitch and tacky materials of synthetic origin in recovered fiber streams often cause serious deposit problems on papermaking equipment. Ideally such materials would be completely removed in processes such as screening, cleaning, washing, or flotation de-inking. In practice, tacky materials that remain in the fiber furnish can build up within paper machine headboxes, forming fabrics, press sections, and dryer sections, reducing production efficiency. Product quality is likely to suffer, especially if deposited material ends up in the sheet. This review considers a variety of chemical additives that papermakers have used to combat deposit problems. The premise of this article is that knowledge of the chemistry and colloidal behavior of existing deposit-control agents can guide us in the selection, usage practices, and further development of strategies for the control of tacky deposits, especially in the case of pitch, adhesive-based stickies, and wax-like deposits.

Hubbe, M. A., Tripattharanan, T., Heitmann, J. A., and Venditti, R. A. "The Positive Pulse Jar (PPJ): A flexible device for retention studies," Paperi ja Puu = Paper and Timber, 88(1), 39-45 (2006).

A bench-scale apparatus, developed for studies of fine-particle retention, compares effects of contrasting flow conditions and retention chemical strategies, using simulated headbox stock.  The apparatus includes an agitated jar, a forming screen, and a continuous phase of aqueous solution below the screen.  A gear pump provides a constant time-averaged rate of dewatering, and a bellows pump produces a sinusoidal component of flow normal to the screen.  Pulsations of known velocity and displacement distance are used to represent effects due to hydrofoils.  As another alternative, the suspension may be subjected to a uniform time-averaged shear stress during dewatering.  Conditions of flow during dewatering affected not only the efficiency of fine particle retention, but also the distribution of fiber fines and fillers in the thickness direction of the fiber mat.  Retention aid use reduced filtrate turbidity, indicating increased retention efficiency.  Retention also was affected by hydrodynamic shear before dewatering; effects of such shear application were apparent even after subsequent exposure to flow pulsations during dewatering.  The design of the apparatus provides flexibility in evaluating mechanistic questions under quantified conditions of pulsating flow and/or steady shear application to the suspension before or during dewatering.

Lee, S. Y., Hubbe, M. A., & Saka, H. "Prospects for diodiesel as a byproduct of wood pulping - A review," BioResources, 1(1), 150-171 (2006).

Effective utilization of byproducts can affect the profitability of kraft pulping to produce cellulosic fibers from wood.  This review considers opportunities to use tall oil components, obtained from kraft pulping, as a source of raw material for biodiesel fuel, or as a source of additives for petrodiesel.  Considerable progress has been achieved with respect to converting vegetable oils to diesel fuel, and some of what has been learned appears to have potential application for processing of wood-derived fatty acids and related compounds.  Alkaline-catalyzed transesterification strategies, while seemingly well adapted for relatively pure vegetable oil source materials, may not be the best fit for the processing of tall oil fractions.  The promising strategies to consider include acid-catalyzed esterification, enzymatic processes, hydrogenation, and the use of supercritical methanol.

Hubbe, M. A. "Sensing the electrokinetic potential of cellulosic fiber surfaces,"BioResources, 1(1), 93-125 (2006).

The charged nature of a cellulosic fiber surface is expected to play major roles in such phenomena as fiber dispersion, flocculation, adhesion, and adsorption of polyelectrolytes.  This review focuses on the evaluation of such charges by means of electrokinetic measurements, with emphasis on the fiber-pad streaming potential technique.  Results of recent experiments suggest that a continuous network or networks of pores below the outer surface of a kraft fiber can significantly contribute to observed streaming potential data.  At present it is not clear whether the main subsurface contributions to the observed electrokinetic effects come from fibrillar layers on the fiber surfaces or from systems of nanopores within the cell walls of fibers.  Based on the literature it is possible to suggest two conceptual models to account for the fact that the streaming potential of polymer-treated fibers can change in sign, dependent on the concentration of salt.  Additional research is needed to clarify various theoretical and practical points.  There may be opportunities to make more effective use of streaming potential tests in the future by carrying out such tests at reduced salt levels.

Wang, Y., Hubbe, M. A., Sezaki, T., Wang, X., Rojas, O. J., and Argyropoulos, D. S. "The role of polyampholyte charge density on its interactions with cellulose," Nordic Pulp & Paper Research Journal, 21(5), 158-165 (2006).

Polyampholytes offer considerable promise as dry-strength additives, but the molecular mechanism involved in their adsorption needs to be better understood.  Amphoteric terpolymers of acrylamide, itaconic acid, and N-[3-(NN’,N’-dimethylamine)propyl]acrylamide (DMAPAA) with a constant ratio of basic to acidic groups (5:4) were prepared by random polymerization.  The basic groups ranged from 2.5 to 20 mole percent in the terpolymers.  Analysis by 1H and 13C nuclear magnetic resonance revealed near-quantitative agreement with the make up stoichiometry.
Streaming potential tests showed significant effects of polyampholyte adsorption, depending on the charge density of the polyampholyte, its level of addition, the pH, and the background electrolyte.  Polyampholytes having higher density of ionizable groups yielded more positive streaming potential at low pH values and more negative streaming potentials at high pH values, compared to polyampholytes of lower charge density.  At the extremes of pH, e.g. pH=3 and pH=11, the effects of a polyampholyte on streaming potential were similar to those of single-charged polyelectrolytes having a matched degree of substitution of charged monomeric groups.  Except for the sample having the lowest density of charges, all of the polyampholyte samples showed a broad maximum in adsorbed amount vs. pH within the range of about pH=5 to pH=9, which is intermediate between the pKa values of the respective charged groups.

Hubbe, M. A., Emerging Technologies in Flocculation, Pira International, Leatherhead, UK, 2005.

The tendency of fibers used in paper manufacture to become entangled, often leading to a flocculated structure and appearance of paper products, has a huge but often overlooked economic impact. Recent work suggests that if it were practical to form perfectly uniform paper, the tensile strength might be as much as twice that of conventionally formed paper. That implies that there is untapped potential to achieve equivalent product performance with less material. Even if advances in technology can reach only part way to the ideal goal of "perfectly formed paper," the potential savings are of the order of magnitude of tens of billions of Euros per year. In addition to materials savings, paper's uniformity is known to have a major impact on such processes as coating, printing, and the high-speed handling of paper in automated equipment. What can today's paper technologists do to minimize fiber flocculation and to reap benefits of more uniform paper and paperboard? This report focuses on a variety of concepts for managing flocculation. Some of these concepts are reasonably well established, and others have not yet been convincingly demonstrated. Mechanical and hydrodynamic principles underlie many of the most promising strategies. Others strategies focus on the selection and use of various wet-end chemical additives. Certain chemicals can be used in combination with hydrodynamic shear to produce more uniform paper, often at a higher speed of the paper machine. Today's paper technologists also have something else working in their favor; various methods have become available for both online and laboratory evaluation of flocculation.The following topic areas are covered in this report:
- The definition and importance of flocculation
- Measuring the consequences of flocculation
- Advances in mechanical and hydrodynamic aspects of flocculation
- Advances in chemical aspects of flocculation
- Advances in flocculation measurements
- Emerging strategies for management of flocculation

Hubbe, M. A., "Dry-Strength Development by Polyelectrolyte Complex Deposition onto Non-Bonding Glass Fibers," J. Pulp Paper Sci. 31 (4): 159-166 (2005).

Sheets formed from glass microfibers had almost zero tensile strength in the absence of polymer treatment, but paper-like dry-strength was achieved if fiber suspensions were treated with combinations of a cationic and an anionic polyelectrolyte before sheet formation. Strength increases generally were maximized when the ratio between the cationic poly-(diallyldimethylammonium chloride) and carboxymethylcellulose was within about 2:3 and 3:2 stoichiometry of charged groups on the macromolecules. Sequential addition of the polyelectrolytes to fiber slurry generally yielded higher strength than pre-mixing the polyelectrolytes before their addition. Significant effects were observed, depending on the ratio of the two polyelectrolytes, optional cationic pretreatment of the fibers, salt concentrations, and the elapsed time between mixing of polyelectrolytes and their addition to a fiber slurry. Time-dependent electrostatic interactions appear to control the deposition of polyelectrolyte complexes, and it was found that the details of chemical addition strategies can have major effects on the results.

Hubbe, M. A., "Mechanistic Aspects of Microparticle Systems," Tappi J. 4 (11): 23-28 (2005).

Uses of specific microparticle programs and applications will be considered in the following chapters, but there seem to be some common features with respect to "how these programs work." This section will consider mechanistic aspects of microparticle programs in general, weighing evidence for and against various concepts. In principle, an understanding of the mechanisms may make it easier to optimize and control additives flows in a microparticle system. Also there may be clues in the mechanisms that can lead to future developments.

Bastidas, J. C., Pawlak, J. J., Venditti, R. A., Heitmann, J. A., Hubbe, M. A., and Dadla, J. F., "Gypsum-Cellulose Interactions - A Colloidal Probe Microscopy Study," Proc. 13th Internat. Symp. Wood Fiber Pulping Chem., 59th Appita Annual Conf., Vol. 2, New Zealand Forest Council, 2005.

Drywall, which is made primarily of a calcium sulfate dihydrate (gypsum) core with paper on both sides, is one of the most widely used construction materials. Because board failure often occurs at the gypsum core/paper interface, it has become important to know the exact nature of the gypsum/cellulose bond and how crystal morphology affects it. This study provides data about the nature of this interaction by means of AFM and Colloidal Probe Microscopy. These methods made it possible to distinguish among the different crystal faces and their respective interactions with cellulose. Measured in air, the adhesive forces between the AFM tip and the different faces varied according to f(010) < f(120) < f(111)  at 50 % relative humidity. The differences in adhesive force with the different gypsum crystals face can be attributed to the differences in surface chemistry. The information obtained in this study will help guide improvements in the gypsum wallboard production process to obtain better bonding between the crystal and the paper.

Lofton, M. C., Moore, S. M., Hubbe, M. A., and Lee, S. Y., "Polyelectrolyte Complex Deposition as a Mechanism of Paper Dry-Strength Development," Tappi J. 4 (9): 3-7 (2005).

Dual-polymer treatments involving a high-charge cationic polymer followed by anionic carboxymethylcellulose (CMC) increased the strength of handsheets formed from the fiber fraction of recycled xerographic copy paper. The amount of the first additive, poly-diallyldimethylammonium chloride (poly-DADMAC), was varied, whereas the amount of CMC was held constant. Results contrasted with earlier work, in which maximum strength was obtained when the amount of poly-DADMAC was just sufficient to saturate the adsorption capacity of unbleached kraft fibers. Rather, in the case of recycled copy paper, significantly higher tensile strength was obtained when the poly-DADMAC addition exceeded the saturation level by a factor of ten. Tests were performed to evaluate a hypothesis that the strength increase was due to polyelectrolyte complex (PEC) formation in the bulk phase, followed by deposition of PECs onto the fibers. Pre-formed complexes were retained efficiently by the fibers, especially if their surfaces had been pretreated with a saturation level of poly-DADMAC. Surprisingly, such pretreatment increased the retention efficiency of all of the PEC mixtures tested, regardless of which sign of charge was in excess. The results suggested that PEC deposition yielded an additional increase of about 13% in dry strength, beyond what could be achieved by treatments not involving complexation.

Hubbe, M. A., "Paper," in Kirk-Othmer Encyclopedia of Chemical Technology, Online Edition, Wiley, New York, 2005.

Paper can be defined as sheet material comprised of small, discrete fibers that are bonded together. The process of paper formation involves dewatering an aqueous suspension, followed by drying. In most cases the fibers are cellulosic, and hydrogen bonds are an important contribution to the strength of the product. The term paperboard is used in cases where the product is thicker, heavier, and less flexible than conventional paper. In addition to fibers, modern paper often contains substantial amounts of minerals, such as calcium carbonate or kaolin clay. Other components, usually at lesser quantities, can include starch, modified starch products, synthetic polyelectrolytes, and a variety of other additives. Though there is a tradition of hand-made papermaking, going back almost two millennia, most modern paper is manufactured on large, highly automated machines. The fiber slurry is formed and dewatered on a continuous fabric screen or sandwiched between a pair of such screens. Though most of the water used in this process is recycled multiple times, the paper industry remains a major user of fresh water. Substantial gains have been achieved to minimize the loss of fibers and other solid components from the process. Likewise, progress has been achieved in reducing the amount of energy expended in the drying of paper, primarily through increases in the proportion of water that is removed by pressing, rather than evaporation. After reviewing paper's distinguishing characteristics and history, the present chapter describes paper's chemical composition, physical properties, preparation of the fibers, the use of chemical additives, formation, pressing, and drying of the sheet, coating and converting of paper, issues related to the environment and manufacturing efficiency, and a summary of common grades of paper and paperboard

Hubbe, M. A., "Microparticle Programs for Drainage and Retention," in Microparticles and Nano- Microparticles for Papermaking, J. Rodriguez, Ed., Chapter 1, TAPPI Press, (2005).

McNeal, M. R., Nanko, H., and Hubbe, M. A., "Imaging of Macromolecular Events Occurring during the Manufacture of Paper," Proc. XIII Fundamental Research Symposium, Cambridge, 2005.

A novel transmission electron microscopy (TEM) technique, developed to observe the nano-scale interactions of polymeric additives and cellulosic fibrils under idealized laboratory conditions, was applied for the first time in a comprehensive study of the colloidal interactions within a mill producing light-weight coated publication paper. The technique allows the observation of incremental changes in the nano-scale appearance of the papermaking slurry as successive additives are introduced to the system. Such changes include the coagulation of colloidal and dissolved substances present in thermomechanical (TMP) pulp after the addition of a low molecular weight, high charge density polymer, and the subsequent flocculation of the coagulated matter, hydrophobic materials, and fines following the introduction of talc, aluminum sulfate, a high mass cationic polyelectrolyte, and silica nanoparticles. The new results demonstrate that the TEM technique can be applied even in systems as complex as commercial papermaking, leading to a more accurate understanding of what happens on a macromolecular level.

Rojas, O. J., Byrd, M. V., Hubbe, M. A., and Claesson, P. M., "On the Origins of Adhesion in Papermaking Systems," Proc. XIII Fundamental Research Symposium, Cambridge, 2005.

Polyelectrolytes are commonly used as additives to control colloidal stability and adhesive properties of surfaces. This investigation is related to the latter case which is relevant to several papermaking processes such as pretreatment of filler particles with cationic polymers (e.g., polyethyleneimine) to increase deposition on pulp fibers or the development of dry strength. The dry strength of paper is often increased by addition of cationic starch or acrylamides to the fiber furnish, which is subsequently dried. The cationic polymer adsorbs to the negatively charged fibers and mediates an increased fiber-fiber bond. It has been reported that the dry strength of the paper increases with decreasing charge density of the polymer, presumably due to increased polymer-polymer interpenetration and due to increased viscoelastic losses that occur during the rupture of the paper sheet under strain.

Hubbe, M. A., "Why Do Different Charge Demand Tests Give Different Endpoints?" Proc. Pira 2005 Sci. Tech. Advan. Wet End Chem., Lisbon, Portugal, Pira International, Leatherhead, Surrey, UK, 2005.

Have you ever encountered situations where two people, both measuring the same samples taken from a paper machine system, have reported sharply different results for cationic demand tests? Such situations actually are quite common. A lot of needless energy can be spent trying to figure out which of the two sets of data is "correct." Fortunately, there are some understandable reasons to expect variations in the details of charge titration tests to yield significantly different results. By keeping these issues in mind, it is possible to get beyond questions of the correctness of different procedures. The end goal should be to improve the reproducibility of the results of charge demand titrations and to interpret the results with greater confidence

Hubbe, M. A., and Zhang, M., "Recovered Kraft Fibers and Wet-End Dry-Strength Polymers," Proc. TAPPI Practical Papermakers Conf., TAPPI Press, Atlanta, 2005.

The drying and recycling of paper profoundly affects the bulk and surface properties of kraft fibers. Recovered kraft fibers tend to be less porous on a sub-microscopic scale, less flexible, and less able to swell with water, compared to never-dried, refined fibers. Recovered fibers also tend to be less able to form inter-fiber bonds. This review considers how changes associated with the drying and recycling of kraft fibers affect their interactions with dry-strength polymers such as cationic starch, copolymers of acrylamide, and high-charge cationic polymers. A key finding of recent research is that the listed changes in fiber properties occur independently of whether or not dry-strength polymers are present. There are two main ways that strength-enhancing additives can compensate for losses in bonding ability. First, dry-strength polymers present in the original paper can contribute to bonding when the same material is recycled. Second, additional wet-end polymers applied during production of the recycled paper can help compensate for deficiencies of bonding ability. Recently a dual-polymer dry-strength program was adjusted to match the ability of recovered kraft fibers to retain cationic polymers. This approach makes it possible to tailor a treatment system to the type of furnish that is being used.

Hubbe, M. A., and Rojas, O. J., "The Paradox of Papermaking," Chem. Eng. Education 39 (2 ): 146-155 (2005).

Students and educators in chemical engineering, are you aware of the paper industry and its impact in our society? With retirements and with changing technology there is a continual need for new technical and scientific skills to face the challenging goals of our times. The purpose of this article is to introduce some intriguing aspects of papermaking technology. The paradoxical nature of the papermaking process is sure to capture your interest and imagination.

Welf, E. S., Venditti, R. A., Hubbe, M. A., and Pawlak, J., "The Effects of Heating Without Water Removal and Drying on the Swelling as Measured by Water Retention Value and Degradation as Measured by Intrinsic Viscosity of Cellulose Papermaking Fibers," Prog. Paper Recycling 14 (3): 1-9 (2005).

The effects of heating without water removal and drying of bleached kraft fibers were separately investigated. Water swellability as measured using a water retention value method (WRV) and cellulose degree of polymerization as measured using a viscosity method were used to gauge the effects of such treatments on fibers. The drying of fibers at temperatures above 100°C resulted in significant decreases in WRV, as expected. However, heating fibers without water removal at the same temperatures resulted in a decrease in WRV much less than caused by drying. Drying at high temperatures reduced the cellulose viscosity only slightly, whereas heat treatment without water removal at high temperatures resulted in much greater losses in cellulose viscosity. The results of this study indicate that the time-temperature-humidity history of a fiber during papermaking and paper recycling can produce fibers with very different papermaking qualities.

Hubbe, M. A., "Acidic and Alkaline Sizings for Printing, Writing, and Drawing Papers," Book and Paper Annual 23: 139-151 (2005); also in Proc. Contemp. Machine-made Paper, Amer. Inst. Conservation Historic Artistic Works, Oct. 20-23, 2004, Dalton, MA

This review of paper sizing systems describes a recent, quiet revolution with respect to the chemicals used during the manufacture of paper. Before this revolution the primary means of imparting water-resistance to mass-produced paper involved rosin and alum, the latter of which is highly acidic. During the 1980s, and continuing up to today, there has been a dramatic shift to new sizing chemicals that employ an alkaline buffering system. As a side benefit of this change, most printing, writing, and drawing papers now made in the US tend to be brighter and more resistant to embrittlement during storage. Perhaps surprisingly, however, the roots of the revolution may have had little to do with paper's permanence.

Hubbe, M. A., Moore, S. M., and Lee, S. Y., "Effects of Charge Ratios and Cationic Polymer Nature on Polyelectrolyte Complex Deposition onto Cellulose," Indus. Eng. Chem. Res. 44 (9): 3068-3074 (2005).

Sequential addition of poly-diallyldimethylammonium chloride, which is highly cationic, followed by anionic carboxymethylcellulose, has been found to promote inter-fiber bonding during the manufacture of paper, with potential benefits to the recycling of fibers. The present results help to confirm a hypothesis that observed strength gains, in cases where the amount of the first additive exceeded the adsorption capacity of the fibers, were due to formation of polyelectrolyte complexes in the solution phase, followed by their deposition onto fiber surfaces. Complex formation and retention of complexes on fiber surfaces occurred efficiently over a wide range of polymer charge ratios, cationic polymer attributes, and other conditions, regardless of whether or not the fibers had been pre-treated to reverse their net charge.

Hubbe, M. A., Emerging Technologies in Wet End Chemistry, Pira International, Leatherhead, UK, 2005.

Do today's papermakers have what it takes to remain competitive in the years ahead? The answer may depend on how well they make use of emerging technologies, applying recent advances in various branches of science. At the wet end of a paper machine, papermakers already use various chemical additives to enhance product end-use performance and to enhance the efficiency of the manufacturing process. This report looks at emerging strategies that can allow future papermakers to leverage their investments in papermaking equipment and to face new challenges. Such challenges include new end-use applications for paper, a need to reduce costs while maintaining quality, efforts to increase production rates, increased paper recycling, reduced fresh-water use, and increasing competition. Tomorrow's papermakers will face a daunting task of competing not only with each other, often across international boundaries, but also with plastic, electronic media, and a variety of other technology platforms that presently we can only imagine. While this report cannot possibly anticipate all the challenges that papermakers will face in the future, emphasis is placed on the following critical areas of emerging technology:
- Nanotechnology in the wet end
- New wet-end starch technologies
- Process control developments for wet end additives
- Changes in the chemical environment of the wet end
- Efforts to enhance the performance of wet end additives
In each of these key areas it is possible to discern some promising strategies that can be used by papermaking technologists in the coming years. The present report aims to help with decisions to apply new technologies judiciously and effectively to meet both longer-term and shorter-term goals.

Hubbe, M. A., and Wang, F., "Charge-Related Measurements - A Reappraisal. Part 2: Fiber-Pad Streaming Potential," Paper Technol. 45 (9): 27-34 (2004).

Continuing a theme introduced in Part 1, the present article addresses concerns raised in 1995 about the use and interpretation of charge-related measurements. The "fiber-pad streaming potential" method is becoming increasingly popular at paper mills and in the research labs of companies involved with papermaking technology. One drawback of the method, as it is commonly practiced, involves a lack of calibration to more fundamental quantities, such as zeta potential. Nevertheless, progress has been achieved with respect to the precision of the method, especially at increased levels of salinity. Also, one can avoid many theoretical difficulties by using the method to determine endpoints of charge titrations. With these considerations in mind, fiber-pad streaming potential tests can reveal important information about the charge-related properties of fiber suspensions.

Hubbe, M. A., and Chen, J., "Charge-Related Measurements - A Reappraisal. Part 1: Streaming Current," Paper Technol. 45 (8): 17-23 (2004).

A 1995 article in this magazine raised concerns about the use and interpretation of two kinds of measurements that are being carried out in paper mills to evaluate the electrical charges at surfaces in fiber slurries. This article relates to the streaming current method, which is widely used for endpoint detection when testing the charge demand of whitewater or filtrate samples from fiber stock. Although there is still some truth in the statement that the "streaming current detector has no established theoretical basis," subsequent work has helped to define ranges of experimental conditions within which the test gives reliable results. Also, some specific sources of interference have become better understood.

Hubbe, M. A., Chen, J., and Heitmann, J. A., "Measurement and Impact of Charge: A Practical Guide," Solutions! 87 (11): 47-49 (2004).

The electrical charges on the surfaces of fibers and other materials in a papermaking furnish have profound, but subtle effects on both the process and the product. Because "charges" are invisible, they are sometimes overlooked as a source of operational problems and variability. However, the balance of surface charges within a paper machine system can directly affect the performance of retention aid chemicals. Low or variable retention of fine materials during paper formation can lead to other problems. Charge also can impact such things as dewatering rates, sizing efficiency, and deposit control.

About three years ago at NC State University we began a detailed study of one of the most widely used methods for charge determination - the streaming current titration method. One of us (Chen) earned a PhD degree in the process. Details of our research results have appeared or will appear elsewhere (see, for instance Colloids and Surfaces 223: 215, 2003). During this work, and also while putting together and checking the literature review section of the thesis, we have had occasion to think about practical implications of charge measurements. Though the opinions expressed below are our own, we need to acknowledge the substantial research progress by others that helped lead us to the following general conclusions.

Chen, J., Heitmann, J. A., Chang, H.-M., Hubbe, M. A., and Venditti, R. A., "The Effect of Paper Additives on Toner Agglomeration during the Recycling Process," Prog. Paper Recyling 13 (14): 16-23 (2004).

One of the principal contaminants in recovered office paper is toner inks. These toner inks can be removed by agglomeration, followed by conventional screening and cleaning techniques. However, it has been found that, for some types of toner, various paper chemicals can interfere with the agglomeration process. In this research two types of toner were investigated. One toner agglomerated well under most conditions, while the other performed less well and was more susceptible to adverse effects by a variety of paper chemical additives. The surface properties of the two toners were examined, and a model system was used to determine how various copy paper additives influenced agglomeration behavior. It is hypothesized that cationic polymers adsorb onto negatively charged toners and reduce their hydrophobicity, which interferes with the agglomeration process. Market pulp, cured toners, and 1-octadecanol were used as a basic model system. The effect of additives such as calcium carbonate, cationic and anionic starches, polyamine, poly-DADMAC, and polyacrylamide were investigated. It was found that the toner that agglomerated well was uncharged, while the more difficult to agglomerate toner was negatively charged. For the anionic toner, cationic hydrophylic polymers had very adverse effects on agglomeration, and it is believed that this is because these polymers are adsorbed onto the toner. It was found that the cationic polymers can be adsorbed onto the agglomerating agent, causing dispersion and failure of the agglomeration process. Several chemicals which would reduce this type of problem were investigated. They helped to confirm the mechanism and also offer possibilities of treatment of the problem in commercial systems.

Hubbe, M. A., and Gill, R. A., "Filler Particle Shape vs. Paper Properties - A Review," Proc. Spring Tech. Conf., TAPPI Press, Atlanta, 2004.

Contrasting shapes and sizes of mineral filler particles provide today's papermaker with many options to affect paper properties. One can choose between plate-like clay products, irregular-shaped products of grinding, and a diverse assortment of filler shapes that can be achieved by mineral precipitation methods. This review considers the connection between filler morphology and such attributes as apparent density, opacity, strength, and demand for sizing chemicals. Although no one type of filler product will suit every application, published information can help the papermaker deal with a series of compromises. Plate-like particles can be effective for paper products having a high apparent density. More rounded, solid-form particles tend to minimize the demand for sizing chemicals and generally allow more rapid dewatering. Particles with internal voids general offer high light scattering ability, contributing to opacity. Though there is often an inverse relationship between light scattering and strength, it is possible to design fillers that achieve a more favorable balance between these two attributes.

Rojas, O. J., and Hubbe, M. A., "The Dispersion Science of Papermaking," J. Dispersion Sci. Technol., J. Dispersion Sci. Technol. 25 (6): 713-732 (2004).

Paper is formed from a slurry of fibers and much smaller particles that are often called "fines." Ahead of the paper forming process the slurry is subjected to a series of steps, including treatment with polyionic species and passage through unit operations that impose shear forces on the fluid mixture. These steps alternately disperse the solids apart or re-gather them back together. The overall process is optimized to achieve a highly uniform product, while at the same time achieving high efficiency of retaining fines in the sheet and allowing water to drain relatively quickly from the wet paper as it is being formed. As we approach the 1900-year anniversary of the first detailed account of the papermaking process, it is the goal of this review to explore the scientific principles that underlie the art of papermaking, emphasizing the state of dispersion of the fibrous slurries during various procedural phases of the manufacturing process. Some concepts that arise out of the experience of papermakers have potential applications in other fields.

Chen, J., Hubbe, M. A., Heitmann, J. A., Argyropoulos, D. S., and Rojas, O. J., "Dependency of Polyelectrolyte Complex Stoichiometry on the Order of Addition. 2. Aluminum Chloride and Poly-vinylsulfate," Colloids Surf. A 246 (1-3): 71-79 (2004).

In the first part of this series it was shown that the stoichiometry of complexation between oppositely charged polyelectrolytes became increasingly dependent on the order of addition as the concentrations of monovalent and divalent ions were increased. This study considers the effect of aluminum ions on titrations between solutions of a strong poly-acid and a strong poly-base. In addition, the titratable charge of aluminum ion itself was also investigated. It was found that aluminum ions can interfere with the results of charge titrations, and stoichiometric relationships fail to explain the observed results. The word "interfere" implies an unpredictable effect on titration results. Several factors affect this interference. However, by controlling solution pH and degree of charge neutralization of aluminum ions, the titratable charge of the system can be estimated by streaming current titration. The results are consistent with the presence of aluminum polynuclear species within the ranges of aluminum and base addition where the highest titratable charge was reached.

Hubbe, M. A., "Pulp and Paper Chemical Additives," Encyclopedia of Forest Sciences, Chapter (MS 135), Elsevier Science and Technology. (2003).

Chemical additives can be critical to the economic viability of paper machines. Relative to fibers (see Chapters 2 through 6) other materials are present in paper and paperboard at much lower levels. However, additives allow papermakers to differentiate their products to meet the differing needs of customers. They also use additives to make their operations more efficient. This chapter considers the most widely used papermaking additives, focusing on their composition, their modes of preparation and use, and their impacts on either product attributes or process efficiency. The fact that relatively small amounts of additives can make huge differences makes this a fascinating field of work and study.

Hubbe, M. A., Tripattharanan, T., Heitmann, J. A., and Venditti, R. A., "The 'Positive Pulse Jar' (PPJ): A Flexible Device for Retention Studies," Paperi ja Puu 88 (1): 39-45 (2006).

A bench-scale apparatus for studies of fine-particle retention was demonstrated, comparing effects of contrasting flow conditions, with or without retention chemical addition, to a simulated headbox stock. The apparatus consisted of an agitated jar with a forming screen on the bottom and a continuous phase of aqueous solution below the screen. A positive displacement gear pump produced a constant time-averaged rate of dewatering, and a bellows pump was optionally used to produce an additional sinusoidal component of flow normal to the forming screen. Pulsations of known velocity and displacement distance were used to represent effects due to hydrofoils. As another alternative, the suspension was subjected to a uniform time-averaged shear stress during the dewatering. It was shown that the conditions of flow during dewatering affected not only the efficiency of fine particle retention, but also the distribution of fiber fines and fillers in the thickness direction of the fiber mat. Under any given set of flow conditions, retention aid use reduced the filtrate turbidity, indicating increased retention efficiency. Retention also was affected by exposure of the stock to hydrodynamic shear before dewatering; effects of such shear application were apparent even after subsequent exposure to flow pulsations during dewatering. The design of the apparatus provides flexibility in evaluating a variety of mechanistic questions under quantified conditions of pulsating flow and/or steady shear application to the suspension before or during dewatering.

Tripattharanan, T., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Effect of Idealized Flow Conditions on Retention Aid Performance. 1. Cationic Acrylamide Copolymer," Appita J. 57 (5): 404-410 (2004).

The performance of a cationic acrylamide copolymer retention aid was evaluated with respect to five contrasting flow conditions applied either before or during the formation of a fibre mat. Different levels of pre-shearing of a simulated fine-paper headbox stock were applied after chemical addition, but before constant-rate dewatering. Dewatering conditions included simple filtration, flow pulsations of known amplitudes and frequencies of normal to the forming screen, and continuous stirring during dewatering either with an impeller or at a uniform time-averaged shear rate. Under all conditions of flow the retention aid reduced the turbidity of the filtrate, consistent with improved retention of fine materials. However, the effectiveness of the polymer was irreversibly decreased by high shear before dewatering. The irreversible loss was observed even when the slurry subsequently was subjected to vigorous flow pulsations during dewatering. Results were consistent with a polymer-bridging mode of retention aid action.

Tripattharanan, T., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Effect of Idealized Flow Conditions on Retention Aid Performance. 2. Polymer Bridging, Charged Patches, and Charge Neutralization" Appita J. 57 (6): 448-454 (2004).

Retention aids can affect papermaking process efficiency and product quality. The efficiency of these polyelectrolyte treatments may be affected by conditions of flow before and during sheet formation. Four contrasting retention aid systems were compared. Hydrodynamic shear before dewatering decreased the retention efficiency of very-high-mass acrylamide copolymers, consistent with irreversible breakdown of polymeric bridges. Such shear had little effect in the case of a moderately high-mass ethyleneimine copolymer. The relative effectiveness and responses to flow conditions of different polymeric treatments were consistent with concepts of charge neutralization, charged patches, and two types of polymeric bridges. Flow velocity pulsations normal to the plane of the forming screen lowered the retention efficiency for all of the retention aid systems, though not as much as the application of uniform time-averaged shear stress to the suspension during dewatering.

Zhang, M., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Refining to Overcome Effects of Drying Unbleached Kraft Fibers in the Presence or Absence of Sugar," Progress in Paper Recycling 13 (2): (2): 5-12 (2004).

Previous work has shown that drying of chemical pulps results in lower inter-fiber bonding when the fibers are subsequently redispersed and formed into recycled handsheets. It was also found that the strength loss could be decreased if the initial drying was carried out in the presence of relatively concentrated sugar solutions. The present research was undertaken to determine whether or not the effects of drying and or sugar treatment still remain significant after the fibers are subsequently refined. Unbleached kraft fibers were optionally subjected to oven drying in the presence or absence of 10% dextrose solution and then subjected to various levels of refining in a PFI mill. Although significant differences in fiber flexibility were still apparent after 6000 revolutions of PFI refining, there was no residual effect of either drying history or the presence or absence of sugar on the strength of recycled paper subsequently formed from those fibers. While it is understood that application of additional refining energy to recycled fibers can be expected to produce additional fine material, reducing the freeness of the stock, the present results suggest that such refining can play a critical role in overcoming the adverse effects on strength when kraft fibers are dried.

Zhang, M., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Effects of Sugar Addition Before Drying on the Wet-Flexibility of Redispersed Kraft Fibers," J. Pulp Paper Sci. 30 (1): in press (2004).

Paper made from recycled, chemically pulped fibers typically has lower strength than paper made from virgin fibers. This was confirmed with respect to tensile and compression strength for an unbleached softwood kraft pulp. It was also confirmed that the addition of sucrose, at high concentration, to virgin pulp before drying could improve the recycled paper strength, compared to a control with no sugar added. The use of glucose was found to be slightly more effective than sucrose. Fibers treated with the sugars were found to have higher flexibility and water retention values than untreated fibers that had been subjected to the same drying conditions.

Chen, J., Heitmann, J. A., and Hubbe, M. A., "Dependency of Polyelectrolyte Complex Stoichiometry on the Order of Addition. 1. Effect of Salt Concentration during Streaming Current Titrations with Strong Poly-acid and Poly-base," Colloids Surf. 223 (1-3): 215-230 (2003).

Titrations were carried out between solutions of a strong poly-acid (polyvinylsulfate, potassium salt) and a strong poly-base (poly-diallyldimethylammonium chloride) over a range of salt concentrations. Streaming current analysis of the titration endpoints appeared to show increasing deviations from 1:1 stoichiometry of complexation with increased salt. The results depended on the direction of the titration, such that a stoichiometric excess of the titrant (second additive) was required to achieve a streaming current reading of zero. These symmetrical results, depending on the order of addition, were obtained despite the fact that the plastic surfaces of the streaming current device had a slight negative charge and differing adsorption tendencies for the two kinds of polymer. A qualitative model of molecular events, based on non-equilibrium entrapment of non-complexed polymer segments was found to be inconsistent with results of tests carried out over a range of initial polymer concentration. Results were better described by a qualitative model involving formation of polyelectrolyte complexes (PECs) in solution, in which near-stoichiometric core complexes are stabilized by an excess of the second additive on their surface. Implications of the latter model were compared with the results of turbidimetric tests, aqueous contact angles on polymer-treated plastic surfaces, and microelectrophoresis of PECs. Results of this study have consequences for interpretation of polyelectrolyte titrations, as well as for industrial operations that involve the mixing of oppositely charged polyelectrolytes.

Hubbe, M. A., Jackson, T. L., and Zhang, M., "Fiber Surface Saturation as a Strategy to Optimize Dual-Polymer Dry Strength Treatment," Tappi J. 2 (11): 7-12 (2003).

The compression strength of unbleached kraft handsheets was maximized when the first component of a dual-polymer treatment was added at a level corresponding to saturation of the fiber surface. The saturation level of poly-diallyldimethylammonium chloride (poly-DADMAC), determined by streaming current analysis, also coincided with a maximum in water retention value (WRV) and a minimum in the light scattering coefficient of the paper. Idealized descriptions of the polymer interactions are proposed to explain the observations.

Hubbe, M. A., "Microparticle Programs for Drainage and Retention," in Micro and Nanoparticles in Papermaking, J. Rodriguez, Ed., Chapter 1, TAPPI Press, accepted (2004).

When papermaking technologists use the word "microparticles," usually they mean certain chemical additive programs that can promote the release of water and help retain fine particles during formation of paper. The prefix "micro" is actually somewhat of a misnomer; some of the most commonly used particles, for which this technology is named, have primary diameters in the nanometer range, 1-5 nm. Microparticles, as well as certain analogous papermaking additives that we will call "micropolymers," are useful only when used in sequence with certain oppositely charged high-mass polymers, hence the term "microparticle programs" as used above. This present book serves as a witness to explosive growth. Before 1980 the subject of microparticle technology, as we know it today, did not exist. Papermakers were generally unaware of potential uses of such additives as colloidal silica and bentonite, except for their occasional uses in water treatment or for control of paper's frictional properties. Now there are at least 550 paper machines that have used these two types of very finely divided minerals - in sequence with cationic starch or cationic acrylamide copolymers - to promote drainage and retention. About 300 have been reported to use colloidal silica, and about 250 have been reported to use bentonite. In addition, there are various paper machines that have used, or are currently using, related retention and drainage programs with highly cross-linked anionic polymers [12] or lignin byproducts playing the role of microparticle. The purpose of this introductory chapter is to review the already-extensive literature related to microparticle programs. This includes descriptions of the materials, how they work together mechanistically, and how the papermaker can take advantage of them to increase paper production rates or product quality.

Hubbe, M. A., Venditti, R. A., Barbour, R. L., and Zhang, M., "Changes to Unbleached Kraft Fibers Due to Drying and Recycling," Progress in Paper Recycling, 12 (3): 11-20 (2003) .

Drying of unbleached kraft pulp in the laboratory revealed two main stages in its response to increasing temperature of drying. The first stage was characterized by significant decreases in water retention value, capacity to adsorb a cationic polymer, dry strength, and apparent density of handsheets formed after re-slurrying the pulp with no additional treatment. These changes, which were independent of the drying temperature, were attributed to the action of capillary forces in the closure of micro-pores in the cell wall during the initial drying. The second stage was characterized by further significant decreases in all of the same parameters when drying temperatures became as high as 150 to 175 oC. In addition, high-temperature drying also resulted in a loss of molecular mass of the cellulose, as revealed by viscosity tests. Surprisingly, neither cellulose molecular mass nor water retention was affected to a significant extent by the value of pH prior to drying, within a range of 3 to 8. The results suggest that whereas some irreversible changes in fiber properties are unavoidable during conventional papermaking practices, further losses in the bonding ability of unbleached kraft fibers can be caused by over-drying.

Hubbe, M. A., "Selecting Lab Tests to Predict Effectiveness of Retention and Drainage Aid Programs," Paper Technol. 44 (9): 20-34 (2003); originally published in Proc. 4th Pira Internat. Conf. Sci. Tech. Advan. Fillers & Pigments for Papermakers, Barcelona, Spain, May 20-21, 2003.

This paper compares laboratory test procedures that predict the performance of chemicals used to enhance retention or dewatering during the manufacture of paper. Key points of difference among the various laboratory methods include the presence or absence of fiber mat formation during the test, the optional application of vacuum, the presence or absence of pressure or velocity pulsations during dewatering, and the use of automation in some test procedures. A well-chosen laboratory test can provide useful information without incurring the high cost and risks associated with having to do full-scale evaluations of many different retention and drainage programs and dosage levels. However, it is important to understand the compromises inherent in different lab-scale tests to guard against premature rejection of specific chemical program options.

Wang, F., and Hubbe, M. A., "Charge Properties of Fibers in the Paper Mill Environment. Part 1. Effect of Electrical Conductivity," J. Pulp Paper Sci. 28 (10): 347-353 (2002).

The electrical conductivity of water used in papermaking processes tends to increase due to water conservation efforts. This study concerns the effect of changes in conductivity on the amounts of highly charged cationic polymers required to neutralize the surfaces of fibers, as measured with a fiber-pad streaming potential method. Streaming potential measurements were carried out at relatively high applied pressure to obtain more precise data under conditions of increased electrical conductivity. The amount of cationic polymer (poly-diallyldimethylammonium chloride) required for neutralization of bleached hardwood kraft fiber surfaces, determined by this test, increased moderately as the electrical conductivity was increased from 0.5 to 10 mS/cm. The amount of cationic polymer required also increased with increasing contact time and with decreasing molecular mass of the polymer. Results are consistent with the porous nature of kraft fibers and the effects of salt on the effective size of macromolecules in solution.

Zhang, M., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Can Recycled Kraft Fibers Benefit from Chemical Addition Before They Are First Dried?," APPITA J. 55 (2): 135 (2002)

Over 50 chemical treatments of never-dried pulp were compared relative to the strength of paper made subsequently after the fibers had been dried and recycled once. Treatments having the greatest beneficial effect on the compression strength of recycled unbleached kraft paper tended to be polyelectrolytes of relatively high molecular mass. Many of the most effective treatments, either alone or by sequential addition, included both cationic and anionic functional groups on the polymers. Results were consistent with the persistent nature of charged complexes formed by polyelectrolytes at fiber surfaces, and the contribution of such complexes to inter-fiber bonding, even after drying and recycling.

Wang, F., and Hubbe, M. A., "Charge Properties of Fibers in the Paper Mill Environment. 1. Effect of Electrical Conductivity," J. Pulp Paper Science, in print, Nov. 2002.

The electrical conductivity of water used in papermaking tends to increase over time due to water conservation efforts. This study concerns the effect of changes in conductivity on the apparent surface charge of fibers and its measurement with a fiber-pad streaming potential method. Poly-diallyldimethylammonium chloride was added to vary the observed streaming potential from its initial value to zero. The charge of bleached hardwood kraft fibers, determined by this test, increased moderately as the electrical conductivity was increased from 0.5 to 10 mS/cm. The amount of cationic polymer required to reach neutrality increased with increasing contact time and with decreasing molecular mass of the polymer. Results are consistent with the porous nature of kraft fibers and the effects of salt on the effective size of macromolecules in solution.

Wang, F., and Hubbe, M. A., "Development and Evaluation of an Automated Streaming Potential Measurement Device," Colloids and Surfaces A 194: 221 (2001).

The streaming potential and other colloidal properties of aqueous suspensions of bleached kraft fibers were evaluated by a new laboratory instrument, the Streaming Potential Jar (SPJ). This device provides precise streaming potential data under moderately high electrical conductivity levels of 0.5 to 10 mS/cm. Features of the SPJ include automated operation, rapid acquisition and processing of data, continuous stirring, and applied pressures up to 276 kPa. The SPJ also provides data related to drainage rates and the turbidity of the filtrate. Test results showed a high degree of linearity of the streaming potential signals with applied pressure and very little dependence of the results on the solids levels of the fiber slurries. These results, which are consistent with the Helmholtz-Smoluchowski equation, tend to justify the level of applied pressure used in this work. Changes in streaming potential with increasing pH were consistent with expected dissociation of surface-bound carboxyl groups on the fibers. The absolute magnitudes of the streaming potential values of bleached kraft pulps were strongly affected by increasing concentrations of Na2SO4. However, a high repeatability of measurements was obtained throughout the range of conductivities considered; relative standard deviations of streaming potentials were consistently below 3%. Titrations with poly-(diallyldimethylammonium chloride) yielded curves that had shapes similar to those of parallel tests by micro-electrophoresis; however, the amount of titrant needed to reach the endpoints was about three times higher in the case of the streaming potential tests. The disagreement between the endpoints determined by the two types of test is attributed to a diffusion process of the titrant into the porous fibers.

Chen, J., Hubbe, M. A., and Heitmann, J. A., "Measurement of Colloidal Charge in the Paper Mill by Streaming Current," Proc. TAPPI Papermakers Conf., 2001.

The colloidal charge of process water within a paper mill can profoundly affect process efficiency and product quality. With increased pressure for productivity and reduced costs the need for accurate and reliable charge measurements has become more urgent. But the paper machine environment presents challenges that may limit the accuracy of such tests. Recently the streaming current method has become the most widely used means of charge analysis. This report presents new data, helping to define the range of sample types and electrical conductivity where it is possible to achieve accurate and reliable results from streaming current titrations. Within the limits of these ranges the results are consistent with a model of polyelectrolyte adsorption onto the plastic probe surfaces of the test instrument. Outside of these limits the results may be unreliable.

Zhang, M., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Effect of Chemical Pretreatments of Never-Dried Pulp on the Strength of Recycled Linerboard," Proc. TAPPI Papermakers Conf., 2001.

According to the American Forest and Paper Association (AF&PA) the recovery rate of corrugated boxes used in the US now exceeds 75%. In principle the recycling of boxes saves fiber resources and requires less total energy. However, further progress in old corrugated container (OCC) recycling faces a potential barrier. It is known that recycled kraft fibers have a reduced bonding ability. The approach taken in this study was to pre-treat the never-dried fibers before the first cycle of papermaking. New data have been obtained with never-dried, refined, unbleached kraft pulp. Simple drying, low-shear disintegration, and forming without further refining yielded a loss in compression strength in the range 19 to 26%, depending on the pulp batch. Pretreatment with various chemical agents was able to compensate for some of the strength loss. Two general classes of treatment agent were identified that were able to favorably affect the strength of recycled sheets. Certain low-molecular weight materials such as sucrose appeared to interfere with the mechanism of pore closure during the initial drying. In contrast, certain high-mass polyelectrolytes such as guar gum products, cationic starch, and polyelectrolyte complexes appeared to affect the adhesiveness of the fiber exteriors of the repulped fibers.

Hubbe, M. A., and Wang, F., "Where to Add Retention Aid: Issues of Time and Shear," Solutions! 2002 (3): 61 (2002); TAPPI J. 1 (3): (2002); and Proc. TAPPI Papermakers Conf., 2001; also reprinted in O Papel.

Papermakers continually wrestle with the question of whether to add high-mass acrylamide copolymer retention aids before or after pressure screens in the approach flow to a paper machine forming section. Early addition of a retention aid provides more opportunity for breakage of chemically induced fiber flocs, possibly leading to more uniform formation. Early addition also provides more chance for chemicals to become degraded or lost in the porosity of fiber cell walls. Later addition tends to maximize chemical efficiency in terms of first-pass retention. A new method of fiber floc evaluation was applied in the case of headbox-consistency fiber slurries to help understand what happens to chemically induced fiber flocs when they are exposed to increased time and shear. The extent of flocculation was determined by the force required to move a pair of 6-mm probes through a slurry. Supplementary tests of the streaming potential of fibers were used to help explain the separate effects of time and hydrodynamic shear on the state of flocculation.

Hubbe, M. A., "Reversibility of Polymer-Induced Fiber Flocculation by Shear. 2. Multicomponent Chemical Treatments" Nordic Pulp and Paper Research Journal 16 (4): 369, (2001).

Optical and viscometric tests showed essentially complete dispersal of fiber flocs when polymer-treated chemithermomechanical (CTMP) fiber slurries were exposed to intense shear in a blender. Two types of chemical systems showed evidence that flocs formed again after the shear application were stronger or larger than those in an untreated slurry. Treatments that included poly-diallyldimethylammonium chloride (DADMAC) showed a charge-dependent maximum in the optical test of flocculation that approximately corresponded to charge neutralization. By contrast, treatments involving cationic polyacrylamide (cPAM) following by nano-size anionic materials (microparticles) yielded a net increase in viscometer output after intense shear. In all cases the polyelectrolyte mechanisms holding calcium carbonate filler particles to the fibers or to each other appeared sufficient to withstand intense shear.

Hubbe, M. A., "Method for Determining Electrokinetic Properties of Papermaking Furnish," U. S. Patent 6,176,974, Jan. 3, 2001

A method and apparatus for determining electrokinetic properties of a papermaking furnish includes mixing a sample of furnish in a container with a known amount of a charged additive and then measuring the streaming potential of the resultant ionically modified furnish sample. The amount of charged additive added to the container is increased or decreased as repeated streaming potential measurements are made until a desired streaming potential of the modified furnish sample is obtained. The results, which are expressed as the amount of titrant required to achieve the desired streaming potential in a given volume of furnish, may be used by papermakers to adjust process variables and achieve optimum, stable paper quality and machine runnability.

Wang, F., Tanaka, H., Kitaoka, T., and Hubbe, M. A., "Distribution Characteristics of Rosin Size and their Effect on the Internal Sizing of Paper," Nordic Pulp and Paper Research Journal 15 (5): 416-421 (2000); presentation at International Paper Coating Chemistry Symposium, June 6-8, 2000

It was attempted to systematically elucidate three aspects of acidic and neutral rosin sizing. These were (a) the relationship between sizing efficiency and the retention behavior of rosin sizes at the wet end, (b) the effect of pulp beating and fiber fines on the size distribution and sizing properties of paper, and (c) the distribution characteristics of rosin size on pulp fiber surfaces in internal paper sizing. Pyrolysis-GC and the oxine extraction method were used to determine the retained amounts of rosin size and aluminum in the paper. Scanning electron microscopy (SEM) and SEM-EDXA (energy dispersing X-ray analyzer) were employed to evaluate the distribution of rosin size on the pulp fiber surfaces. Under neutral to alkaline conditions neutral rosin and acid rosin sizes yielded distinctly differing sizing effects. The results depended to a great degree on the chemical stability of rosin particles and the retention efficiency of each type of sizing agent under the wet-end conditions of papermaking. Pulp beating and fiber fines influenced the size distribution and sizing properties of paper. Both pulp beating and the existence of fiber fines were considered as important contributing factors leading to the observed uneven rosin size distribution. Furthermore, the rosin size was unevenly distributed on the fiber surfaces not only for freeze-dried paper, but also for cured paper, and its distribution was similar and correlated to that of aluminum. A continuous rosin size film could not be formed even after drying by heating. It is proposed that an uneven aluminum distribution on fiber surfaces can be a root cause of non-uniform sizing with rosin.

Hubbe, M. A., "Reversibility of Polymer-Induced Fiber Flocculation by Shear. 1. Experimental Methods" Nordic Pulp and Paper Research Journal, in press; presentation at International Paper Coating Chemistry Symposium, June 6-8, 2000

Papermakers desire two seemingly incompatible outcomes. On the one hand, strong agglomeration of fibers and fines can help one to achieve rapid drainage and satisfactory fine-particle retention. On the other hand, papermakers also want uniform distribution of fibers in the sheet. Procedures have been developed in our lab to evaluate effect of different retention and drainage chemical programs under stressed conditions of salt content, fines content, or high levels of charged colloidal matter. In the work described here the same tests were used to compare the reversibility of agglomerative effects of some common classes of retention and drainage programs. Optical and viscometric tests showed increased flocculation following treatment with increased amounts of cationic polyacrylamide. Application of intense hydrodynamic shear caused essentially complete reversal of flocculation. By contrast, treatment with a highly charge density cationic polymer yielded a maximum in flocculation, according to the optical test, at a treatment level corresponding to the point of charge neutralization. Divergent results were obtained when comparing fine-particle retention tests to drainage tests. In general, retention results were consistent with a model in which polymer bridges, i.e. "hard flocs," between fibers may be irreversibly broken by shear. Meanwhile, bonds formed between fibers and fine particles appeared to remain intact. In contrast, drainage results appeared to be more highly dependent on the electrokinetic properties of the furnish, i.e. factors related to "soft floc" formation.

Hubbe, M. A., "Selecting and Interpreting Colloidal Charge Measurements," Proc. Scientific and Technical Advances in Wet End Chemistry," PIRA, Barcelona, June 19-20, 2000.

Achieving an optimum balance between negatively and positively charged materials in a fiber slurry can be critical to the profitable operation of a paper machine. There is no consensus, however, regarding what tests to use and how to interpret the results. Papermakers are free to choose among several competing methods, including micro-electrophoresis, colloidal titrations with a color endpoint, streaming current titrations, and fiber-pad streaming potential methods. Each method has its strengths and weaknesses. It is critical to be aware of the potential weaknesses and interferences with each method before selecting it for a given papermaking application such as process control surveys of paper machine operations. An understanding of potential errors also can improve a user's ability to draw reliable conclusions.

Zhang, M., Hubbe, M. A., Venditti, R. A., and Heitmann, J. A., "Loss of bonding Strength Dye to Drying and Repulping of Kraft Fibers: Effects of Chemical Additives," Proc. International Symposium on Environmentally Friendly and Emerging Technologies for a Sustainable Pulp and Paper Industry, Taipei, Taiwan, April 25-27, 2000.

Chemical pretreatment of never-dried kraft fibers was found to improve the strength of recycled paperboard. Lab tests with guar gum added to unbleached softwood kraft pulp (linerboard furnish) showed that the additive increased the tensile strength and resistance to compression failure. Strength values fell by 25-35% when the same fibers were reslurried and then formed into second generations of paper. However, the strength of the paper made from pre-treated fibers remained significantly higher than the recycled, untreated control. The results suggest a strategy whereby an initial additive or additives to never-dried fibers yield strength benefits that persist over at least one generation of recycled paper. Expected benefits include reduced overall costs for strength-enhancing chemicals, reduced basis weight requirements to achieve product strength requirements, and an ability to use higher levels of waste fibers.

Tests were carried out to shed light on the mechanism of strength loss and the effects of chemicals relative to strength loss when paper is dried and then recycled. The chemical effects on strength appeared to be governed by at least two significant mechanisms. For instance, it was found that pretreatment of the never-dried pulp with a very high level of sucrose yielded an improvement of the tensile strength of recycled paper, compared to untreated fibers that were dried and recycled. This observation is consistent with the known ability of sucrose to penetrate into the fine pores in the walls of kraft fibers. The sucrose-pretreated fibers retained higher levels of water retention value (WRV), indicating a greater degree of swelling when the once-dried fibers were placed back into water. These results with sucrose are consistent with a mechanism in which loss of bonding ability is related to irreversible closure of pores in the fiber cell wall. Contrasting results were obtained when the never-dried fibers were treated with underivatized guar gums. The guar increased the relative strength of both the primary and secondary sheets, but there was no effect on the water-holding ability of the fibers. It is proposed that the guar's mechanistic role is related to its effects on relative bonded area or shear strength of bonds per unit of bonded area.

Olsen, W. L., Zhu, H., and Hubbe, M. A., "Method of Improving Pulp Freeness using Cellulase and Pectinase Enzymes," U. S. Patent 6,066,233, May 23, 2000.

A method for enhancing the freeness of pulp made from secondary fiber is provided by adding an enzymatic mixture comprised of cellulase and pectinase enzymes to the pulp and treating under conditions to cause a reaction to produce an enzymatically treated pulp. The freeness of the enzymatically treated pulp is increased from the initial freeness of the secondary fiber pulp without a loss in brightness.

Chen, J., Hubbe, M. A., Heitmann, J. A., and Chang, H.-M., "The Effect of Paper Additives on Agglomeration During the Recycling Process," Proc. International Symposium on Environmentally Friendly and Emerging Technologies for a Sustainable Pulp and Paper Industry, Taipei, Taiwan, April 25-27, 2000.

A major contaminant in mixed office waste paper is toner inks. One method for removal of these contaminants is chemically aided agglomeration followed by conventional screening and cleaning techniques. Most agglomeration agents are oil-like hydrophobic or amphipathic materials. Because of their hydrophobicity they wet the surfaces of toners and other hydrophobic materials in aqueous suspensions. Thus they have the ability to form bridges and aid toner agglomeration. One very effective agglomerating chemical was found to be 1-octadecanol. Unfortunately, for some types of toner, it has been found that various paper chemicals can interfere with the agglomeration process. This study was focused on the effect of various paper additives on agglomeration of different toners.

Hubbe, M. A., U.S. Patent 5,936,151, Aug. 10, 1999, "Method and Apparatus for Measuring an Electrical Property of Papermaking Furnish."

An apparatus for determining an electrical characteristic [the endpoint of a streaming potential titration] of a papermaking furnish includes a sample chamber having first and second sections for containing a sample of the papermaking furnish. A fiber-collecting screen having a mesh sufficient to inhibit the passage of suspended fibers separates the first and second sections of the sample chamber. Furnish is urged back and forth through the screen in a plurality of cycles so that as the furnish flows in one direction through the screen, a fiber pad is formed adjacent to the screen and as furnish is move through the screen in a second direction, the fiber pad is expelled from the screen back and redispersed back into the furnish sample. A stirrer or mixer assists in removing the fiber pad from the screen and in redispersing fibers comprising the fiber pad back into the furnish sample. A furnish is urged through the screen, electrodes positioned on opposite sides of the screen produce signal outputs corresponding to an electrical characteristic of the furnish [streaming potential]. A voltmeter receives the electrode outputs and measures voltage across the screen. In one embodiment, furnish is moved through the screen by means of a variable volume chamber in fluid connection with the screen and furnish. In an alternate embodiment, fluid is urged through the screen by reciprocating the screen within the furnish sample. Colloidal charge of the furnish may be determined by moving furnish through the screen in repeated cycles as the furnish sample is titrated with a highly charged additive.

Hubbe, M. A., Wagle, D. G., and Ruckel, E. R., U.S. Patent 5,958,180, Sept. 28, 1999, "Method for Increasing the Strength of a Paper of Paperboard Product."

Processes for increasing the [bonding] strength of cellulosic fibers are carried out by contacting relatively dry cellulosic fibers with an agent in particulate or vapor form comprising a carboxylic acid cyclic anhydride at an elevated temperature for a time sufficient to significantly increase the bonding strength of the fibers. The treated fibers bond more readily to one another and they also hold wet and dry strength aids more strongly. Furthermore, the treatment does not significantly affect the internal chemical structure of the fibers so that paper made from the fibers exhibits overall improved dimensional stability.

Hubbe, M. A., "Difficult Furnishes," Proc. TAPPI '99, 1353-1367; literature review and a proposal to broaden the view of what types of paper furnish components need to be considered in relationship to runnability and product quality.

Changes in paper furnish are making it harder to achieve targets of retention, drainage, formation, and strength. This review takes a closer look at components that tend to make furnish difficult. Prime examples are increasing filler levels, dissolved and colloidal anionic materials, high levels of fines, high conductivity, contaminants, and fibers lacking in ability to form bonds. The review also considers chemical additives and strategies which papermakers use to cope with each furnish deficiency and maintain retention, drainage, formation, and strength at desired levels. The chemical additives and strategies can work by affecting the structure, surface area, state of agglomeration, surface properties, or relative bonded area of the components of a paper sheet.

Hubbe, M. A., "Paper: Wetting and Penetration of Liquids into," Encyclopedia of Materials Technologies, Elsevier; Chapter solicited by subject editor.

End-use applications of paper require a wide range of properties with respect to interactions with liquids. At one extreme are tissue papers and toweling. They are designed to imbibe water quickly. At the other extreme are cup-stock and greaseproof papers that are designed to inhibit passage of liquids. It is remarkable the degree to which variations in the processes and chemical additives used in paper can achieve such diverse products. On a microscopic scale paper is porous, directional, and rough. Papermakers and specialists have used two approaches to define and measure wettability and penetration by liquids. On the one hand tests have been carried out involving smooth, flat surfaces or filaments composed of pure materials such as cellulose films or other ingredients that compose paper. On the other hand, the paper industry has developed a wide range of practical, empirical tests that predict aspects of product performance.

Bennett, M. B. O., Crouse, J. W., Hubbe, M. A., and Paukstra, P. M., "Engineers and Papermakers Bond for Better Papermaking at TAPPI's First Superconference," Tappi J. 81 (3): 239 (1998).

Hubbe, M. A., "Surface Analysis of Paper [Book Review]," Tappi J. 80 (5): 239 (1997).

Read this book and you'll never look at paper in quite the same way. This comprehensive text awakens the reader to substantial progress in surface analysis. It also helps make sense of what can otherwise become a bewildering array of complex and expensive analytical tools and methods.

Hubbe, M. A., "Retention Aids," Proc. TAPPI Short Course on Dyes, Fillers, and Pigments, Chicago, April 1995.

The purpose of this course module is to introduce the subject of retention aids. Students will learn about the basic functions, safe use, and chanical nature of the additives most commonly used as retention aids. Widely known theories of zeta potentail and retention aid mechanisms will be summarized. The course module also describes a popular method for evaluating retention aid effectiveness.

Hubbe, M. A. "Colloidal Aspects of Aluminum Chemistry in Papermaking," presented at the ACS Colloids Symposium in Toronto, June 1993.

The trivalent charge and remarkably small size of the aluminum III cation yield unique characteristics. Papermakers have exploited these unique properties of aluminum salts for many years for such applications as pitch control, drainage, retention, and as a mordant for hydrophobic sizing with rosin. In addition to the traditional use of aluminum sulfate ("papermakers' alum"), papermakers now have the options of using partially hydrolyzed polymeric forms of aluminum salts. The choice of additive and dosage level is further complicated by recent trends toward manufacturing at higher pH. The goal of this paper is to provide fresh insights into the mechanism underlying the use of alum and related products by considering their colloidal behavior.

Hubbe, M. A., "Characterization of Liquid Absorption into Porous Media," with M. B. Lyne, presented at TRI/Princeton 62nd Ann. Conf., April 30, 1992.

Dynamic liquid absorption measurements have achieved widespread use within the paper industry for process control and quality assurance. A test developed by J. A. Bristow has enabled papermakers to predict the performance of their paper when used in printing processes where the paper must absorb ink on a millisecond time scale. The results are sensitive to the sample's porosity, surface roughness, and the chemical nature of its surface; these parameters can be separated by analysis of the data. The surface chemistry in some cases has been shown to change rapidly during the first few seconds of contact with a liquid, which results in accelerated adsorption after an initial delay. Since the surface chemistry and porosity of paper are sensitive to adsorption of moisture, it is essential that all tests be carried out under controlled conditions of humidity. The test method is also applicable to other porous sheet materials.

Lisnyanski, K., and Hubbe, M. A. "System for On-Line Measurement of Color, Opacity, and Reflectance of a Translucent Moving Web," U.S. Patent 5,047,652, Sept. 10, 1991.

Systems for the on-line optical measurement of properties of a translucent moving web, such as paper or plastic, as it is continually produced, colored or otherwise converted. Measured properties include color, reflectance, and opacity. A backing roll has a cylindrical or approximately cylindrical surface which comprises at least one optical standard. The roll is positioned such that a circumferential portion of the roll surface contacts the back web surface where the web characteristic is to be measured, with the web curving around the circumferential portion. An optical sensing device is positioned so as to view the front web surface backed by the optical standard or standards. In several embodiments, two sets of reflectance data are collected, one with a "white" optical standard backing and the other with a "black" optical standard backing. The backing roll surface and the optical sensing device can be arranged such that the sensing device either alternately of simultaneously views portions of the front web surface backed by each of the optical standards. In other embodiments, the backing roll has a uniform optical standard surface.

Hubbe, M. A., "How Do Retention Aids Work," Proc. TAPPI Papermakers Conf., 389-398 (1988).

This paper presents a literature review of mechanisms that have been proposed to explain the action of polymeric retention aids used in paper manufacture. The available experimental evidence can be used to support a variety of hypotheses. For instance, do retention aids work by binding the fine particles to the fibers, or by flocculating the filler into aggregates that can be filtered by the fiber mat? Does the mechanism depend on charge neutralization, or on polymeric bridges? The effects of complicating factors such as time, shear, and detrimental substances are discussed briefly.

Hubbe, M. A., "Detachment of Colloidal Hydrous Oxide Spheres from Flat Solids Exposed to Flow. 3. Forces of Adhesion," Colloids Surf. 25: 311-324 (1987).

Colloidal hydrous titania, alumina, and chromium hydroxide spheres were detached from cellulose and glass surfaces by hydrodynamic shear. Independent variables included pH, ionic strength, and the addition of strongly adsorbing ions. The shear stress required for detachment was consistent with a model based on dispersion and electrostatic forces of adhesion. The goodness of the fit of the theory to the data depended on the boundary conditions assumed for the electrostatic forces. In some cases the assumption of constant surface potential was more consistent with the data. In other cases the constant charge assumption yielded a better fit.

Hubbe, M. A., "Detachment of Colloidal Hydrous Oxide Spheres from Flat Solids Exposed to Flow. 4. Effects of Polyelectrolytes," Colloids Surf. 25: 325-339 (1987).

Pretreatment of cellulose and glass surfaces with cationic polyelectrolytes greatly increased the forces needed to detach titanium hydrous oxide spheres. The force of adhesion was as much as 30 times greater than the highest values obtained in the absence of polymers. The hydrodynamic shear stress required for detachment increased with pretreatment level, molecular mass, and decreasing cationic charge of the polymer. The results are consistent with the presence of polymeric bridging between the solids.

Hubbe, M. A., "Retention and Hydrodynamic Shear," Tappi J. 69 (8): 116-117 (Aug. 1986).

Recent articles describe the levels of hydrodynamic shear stress in paper machines. High intensities of shear tend to pull particles of filler pigment and fiber fines from the surfaces of fibers. My purpose here is to compare the levels of shear stress relative to the ability of small particles to remain attached. The results imply that suitable synthetic retention aid systems are more than adequate for the shear stresses in the forming section of the machine. Also, smaller particles are more easily detached than larger particles, under specified conditions of treatment and shear stress.

Hubbe, M. A., "Detachment of Colloidal Hydrous Oxide Spheres from Flat Solids Exposed to Flow. 1. Experimental System," Colloids and Surfaces 16: 227-248 (1985).

This article describes an improved technique for studying the detachment of very small particles from solids walls exposed to turbulent shear flow. The technique is useful as an assay of the strength of adhesion between solids immersed in solution. It is also useful in determining the mechanism by which detachment takes place. The experiment is designed so that the particles rest on a window in the outer annular wall of a system of coaxial cylinders. This arrangement permits more rapid counting of particles remaining on precisely the same area throughout the experiment. Results are presented for the detachment of uniform colloidal hydrous oxide spheres from cellulose and glass substrates. Independently controlled variables included the applied shear stress, the size of the particles, the composition of the aqueous solution, and the time of shearing.

Hubbe, M. A., "Detachment of Colloidal Hydrous Oxide Spheres from Flat Solids Exposed to Flow. 2. Mechanism of Release," Colloids Surf. 16: 249-270 (1985).

Experiments show how small particles are detached from a flat window exposed to turbulent shear flow. The onset of detachment is governed by the component of hydrodynamic forces which pulls the particles in a downstream sense. An adhesive torque opposes the applied hydrodynamic torque. In the rate-determining step a released particle rolls from its initial site of attachment. Resistance to rolling is proportional to the product of the net adhesive force and a characteristic length of the region of contact. The kinetics of release indicate that the process is governed by random events. Continued shearing at the same average shear stress results in continued entrainment of particles. The data are consistent with an idealized model of fluctuations in the local hydrodynamic force within the viscous sublayer of turbulent shear flow. Brownian motion does not properly account for the effect of shear stress on the rate of detachment.

Hubbe, M. A., "Theory of Detachment of Colloidal Particles from Flat Surfaces Exposed to Flow," Colloids and Surfaces 12: 151-178 (1984).

Theoretical models are presented for the detachment of colloidal particles from solid surfaces exposed to shear flow. The models are most relevant to cases of hard, spherical particles that are small enough to display Brownian motion. It is concluded that the component of hydrodynamic force acting parallel to a sheared wall is usually much larger than the lifting forces. Thus, in most cases, one can expect the downstream component of force to govern the critical or rate-determining step in the process of entrainment. Alternative limiting modes of incipient motion, e.g. rolling, sliding, and lifting, can be distinguished, based on the dependency of the shear stress required for detachment on the size of particles. Rate laws for detachment and the dependency of rates on the applied shear stress permit one to discriminate between processes limited by viscous flow, Brownian motion, and fluctuations in hydrodynamic forces. Finally, it is proposed that separate geometric models of sphere-wall interaction can be employed in computing long- and short-range forces.

Hubbe, M. A., "Bonding of Filler to Cellulose: Effects of Cationic Retention Aids," Proc. TAPPI 1984 Papermakers Conf., 23.

Experiments reveal that pretreatment of cellulose film with cationic polyelectrolytes greatly increases the strength of bonding between the film and model filler particles. Levels of hydrodynamic shear required for detachment of spherical colloidal oxides were affected by the dosage, density of charge, and molecular mass of various cationic agents to which the cellulose had been exposed. The most tenacious bonding was generally achieved at high dosage of cationic agents having low to moderate density of charge. Very high molecular mass was not needed in order to form strong attachments. Both branched and linear polymers were found to be effective. The results suggest strategies for improving the retention of filler on paper machines.

Hubbe, M. A., "Adhesion and Detachment of Biological Cells in Vitro," Prog. Surface Sci. 11 (2): 65-137 (1981).

Adhesion between biological cells and various surfaces is explained in terms of various models, including coagulation at primary or secondary minima of free energy, macromolecular bridges or matrices, and specialized structures at the surfaces of some cells. These models are used to predict the magnitudes of forces necessary to detach a cell in the limiting cases of peeling and simultaneous separation over finite areas of contact. Diverse experimental assays of cellular adhesiveness are reviewed and the forces applied to individual cells are estimated. A very wide range of forces applied to cells in different assays suggests that different mechanisms of bonding are dominant for different types of cells and surfaces under various conditions of growth and chemical environment. The peeling mode of separation is most consistent with the magnitudes of applied force used experimentally in the detachment of cells.

Hubbe, M. A., "A Polarization Resistance Corrosivity Test with a Correction for Resistivity," British Corrosion J. 15 (4): 193-197 (1980).

A polarization resistance test that employs three identical sample probes and compensates for the interference of solution resistivity is described. The corrosion test vessel and probes are treated as a conductivity cell for which the cell constant is found using a standard a-c bridge technique. The constant is used to calculate the contribution of ohmic resistance (IR) to the polarization resistance measurements. Data from two- and three-day exposures of mild steel and brass to salt and acid aqueous solutions yield an excellent linear correlation between corrosion rates predicted by the polarization test and measurements of sample weight loss. The procedure offers a potential increase in precision over some other polarization resistance tests, and the apparatus is fairly simple and can be made portable. The procedure is recommended for non-passive alloys and for industrial process water where the corrosion rate is expected to be in the range 0.01-1.0 amperes per square meter and the solution resistivity is below 10,000 ohm-cm.

Hubbe, M. A., "A Modified Reporting Procedure for Polyelectrolyte Titrations," Tappi 62 (8): 120-121 (1979).

Titration of fibrous slurries with polyelectrolytes to determine the surface charge of the slurry solids has been offered by Halabisky as a means of paper machine wet-end control. Further experience has shown that certain modifications in reporting of the titration results lead to the improved reliability and utility of the original procedure.

Hubbe, M. A., and D. F. Bowers, "Survey of White Water Corrosivity in 30 North European Paper Mills," Paper Trade J. 1978: 53-56 (Nov. 1, 1978).

Reuse of paper machine white water has become an almost universal practice within the industry. Energy costs and environmental restraints on effluent discharge have made some form of this practice mandatory. While the closure of white water systems is becoming a worldwide activity, we describe trends in a recent survey of 30 North European papermaking operations.

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