Mini-Encyclopedia of Papermaking Wet-End Chemistry
Additives and Ingredients, their Composition, Functions, Strategies for Use


Composition: The most commonly used surface size additives (in addition to starch) are styrene maleic anhydride (SMA) copolymers, styrene acrylates (SA), alkylated urethanes, and several latex products that include some of the same chemical functionalities. Many of these products are formulated with a strong anionic charge. Usually they are delivered as viscous solutions comprised of the sodium or ammonium salts of the corresponding poly-carboxylic acids.

Function: These materials are not added to the wet end, but they have a close relation and interaction with wet-end additives. Their purpose is usually at least partly the same as that of wet-end sizing agents --reduction in the tendency of water to penetrate into paper. In addition, many of these materials can increase the surface strength of paper and decrease air permeability to a greater degree than a film of starch alone at the paper surface.

Strategies for Use: Briefly stated, successful use of hydrophobic size-press additives can be sensitive to pH. The pH has to be high enough to keep the additives dissolved and to minimize foaming. Defoamer use has to be carefully optimized, since defoamers can work against the desired sizing effect. The performance of many surface size additives can be greatly improved if the paper already contains enough internal sizing agents to keep the size-press starch film near to the paper surface. There has been no documentation of the effects of surface size additives recycled back to the wet end with broke.

Cautions: Size press starch is very hot and may cause burns.

Surface size additives are for strength and optional liquid resistance    

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, .