Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
Composition: Here we are mainly concerned with those additives or byproducts of de-inking operations that are likely to be carried over to the paper machine. Since there are a variety of different de-inking procedures, the nature of such carryover may be very different from case to case. De-inking operations that use flotation are likely to yield some carryover of fatty acid soaps or nonionic surfactants. De-inking operations that involve agglomeration of xerographic toner are likely to contain sparingly soluble nonionic surfactants. Operations that involve bleaching with hydrogen peroxide are likely to contain silicates. In addition, it is likely that the furnish will contain residual xerographic toner, which usually involves carbon-black pigment surrounded by thermoplastic resin binder.
Function: The goal of the papermaker is to use de-inked fiber to make paper that is essentially identical to the same grade of paper made from virgin fiber. The most challenging issues are dirt-counts, brightness, and strength.
Strategies for Use: The best strategies for handling of de-inked pulp all involve the de-inking plant, not the paper machine. Specialists in de-inking technology can provide guidance regarding combinations of screening, cleaning, agglomeration, dispersion, kneading, and floating that will give good efficiency, depending on the product requirements. An often-overlooked part of this process is the need to thicken or wash the final de-inked pulp so that soluble and colloidal material is not passed to the paper machine system. Once on the paper machine, contaminants and de-inking chemicals are likely to cause problems with production efficiency and quality. Addition of talc and other detackifiers to the wet end can help keep stickies in check. The dosage of sizing agent may have to be increased to compensate for the adverse effects of increased surfactant levels on development of hydrophobicity. Defoamers and biocides may have to be increased or changed when de-inked pulp is first introduced. The amount of de-inked pulp in certain fine paper grades may have a practical upper limit because of issues with brightness, cleanliness, friction, caliper, or strength.
Cautions: All recycling operations involve hazards due to the non-uniform nature of the material. Potential hazards include baling wires, hard objects, and toxic substances placed in the bales.
|Schematic of flotation de-inking process|
PLEASE NOTE: Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives. Please send corrections if you find errors or points that need better clarification.
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This page is maintained by Martin Hubbe, Associate Professor of Wood and Paper Science, NC State University, email@example.com .