Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
POLYAMINES (high-charge cationic polymers)
Composition: When papermakers speak of "polyamines," they are most often referring to a series of copolymers of dimethylamine and epichlorohydrin. The repeating unit of the linear form of the copolymer is -CH2-CHOH-CH2-N+(CH3)2-. The presence of a quaternary ammonium group within the backbone of this molecule ensures that it maintains its very strong cationic charge throughout the pH range of most papermaking operations. Manufacturers can include other monomers to achieve branched versions of this molecule. Molecular masses are typically between tens of thousands and hundreds of thousands of grams per mole. The product is usually delivered in solution form, with a solids level between about 10% and 50%, depending on the molecular mass.
Function: Neutralization of excess anionic colloidal charge, especially in the case of neutral or alkaline papermaking; to establish anchoring points for an anionic polyacrylamide retention aid added later.
Strategies for Use: The use and optimization of highly charged additives to a paper machine is never simple. But there is one sense in which the behavior of polyamines is simpler than some other highly charged cationic additives such as alum or PEI. The simplifying attribute of the most commonly used polyamines is that their charge doesn't depend on pH. The quaternary ammonium groups remain cationic throughout the pH values of acidic and alkaline papermaking. There are several things to consider when selecting an appropriate addition point. The first is the fact that these molecules need only a few minutes to partly absorb into the fine pores at the fiber surface. Such molecules then are unavailable with respect to retention and drainage mechanisms. In theory this can be avoided by adding the highly cationic material very late to the process. The other part of the story is that the charge balance of a papermaking furnish needs to be adjusted so that it is optimized and stable well ahead of the addition points for sizing agents, dyes, retention aids, and the like. Very late addition of polyamines sometimes can cause deposition of tacky materials such as dyes, defoamers, and pitch onto pressure screens and headbox surfaces. The best overall rule of thumb is to proceed in small steps with low dosages of polyamine either before or after the fan pump. There are two big exceptions to this rule. One is that polyamine might be added directly to one of the thick stock streams that has been identified as a major source of anionic charge. Another is that the polyamine might be used to precipitate dispersed pitch or stickies onto fibers in a thick-stock stream or chest where there is a high content of tacky materials.
Cautions: Refer to the MSDS and recommended procedures for each product.
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, firstname.lastname@example.org .