Mini-Encyclopedia of Papermaking Wet-End Chemistry
Part Three: Equipment & Unit Operations


When papermakers use the word "sizing" it is sometimes a good idea to ask whether they are referring to internal (wet-end) sizing or surface sizing (at a size press). The function of internal sizing is to increase the resistance to liquid penetration into or through paper. This effect can be achieved under acidic papermaking conditions with rosin and alum. Under alkaline papermaking conditions it is common to use alkenylsuccinic anhydride (ASA) or alkylketene dimer (AKD) for internal sizing. The principle function of surface sizing usually is to strengthen the surface of the sheet with a discontinuous film of inexpensive starch. Some papermakers also add to water resistance by adding hydrophobic polymers such as styrenemaleic anhydride (SMA), styrene acrylate (SA), or alkylated urethane polymers to the sizes press starch solution.

For related information, you might also want to see an essay that is titled "Right Sizing."



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This page is maintained by Martin hubbe, Associate Professor of Wood and Paper Science, NC State University, .