Effects of Temperature, pH and Alkalinity on ASA Sizing in Alkaline Papermaking, 1996 Papermakers Conference Proceedings

The effects of wet end variables, such as the temperature and pH of the stock, and the effects of dissolved calcium carbonate on the ASA sizing process were evaluated one at a time under laboratory conditions. This information is valuable when ASA sizing system is optimized. The use of Alkenyl Succinic Anhydrides (ASA) in alkaline hydrophobization of paper is based on the reactive succinic anhydride group which forms a covalent bond with the hydroxyl groups of cellulose. The reactive group can, however, lose its sizing ability, if the surrounding conditions favour the hydrolysis reaction. In this study it was concluded that the prerequisite for control of the ASA sizing process is control of the pH of the stock. In the case of the ASA sizing process the pH is preferably buffered to 7.5-8.4 with a carbonate filler. The amount of dissolved calcium carbonate can be kept low at the relatively high temperature in the wet end and at the pH range 7.5-8.5. An optimal concentration of hydroxyl ions and alkalinity accelerates the development of ASA sizing under these conditions. Furthermore, the ASA hydrolysis loss is minimized, the amount of Ca-deposits is smaller, and a good filler retention can be achieved.