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

SIZING AGENTS (internal)

Composition: Even when one qualifies the term "sizing agent" with the word "internal," it still can refer to several different materials. Some of these are discussed in greater detail elsewhere in this series. To perform their function in resisting penetration of water or other liquids into paper, sizing agents all contain some type of low-energy chemical group. These may include fatty acid "tails," typically in the range of 14 to 22 carbons in length. Alternatively, these may consist of fused hydrocarbon rings, as in the case of rosin products. Every successful sizing agent contains some handle by which the molecules can be retained, anchored and oriented. In the case of rosin products, this anchoring point consists or one or more carboxyl group per molecule. In the case of ASA or AKD it consists of a reactive ring that is theoretically capable of forming an ester bond with hydroxyl species at the surface of paper. The degree to which such reactions actually take place under the conditions of papermaking has been a matter of debate and experimentation.

Function: To increase the resistance to penetration of paper by water or related liquids

Strategies for Use: More specific guidelines are provided in the discussions of such sizing agents as rosin soap size, rosin emulsion size, alkenylsuccinic anhydride (ASA), and alklylketene dimer (AKD). The general strategy involves such steps as (a) making sure that the size is prepared in a form that will distribute very well with the furnish, (b) mixing it with the furnish at a point where adverse interactions with the furnish are minimized, (c) using the best sequence and ratio of alum or PAC in the case of rosin sizes, (d) retaining it well, and (e) possibly adjusting the conditions of the production environment to promote more rapid cure.

Cautions: Consult the MSDS of each chemical product.

pH ranges for different sizing agents    

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, .