Effect of cationic polyacrylamide on colloidal wood resin

Closing the water circulation system in a paper machine decreases the fresh water usage but raises the amount of dissolved and colloidal substances (DCS) in the circulation water. The dissolved substances are mainly composed of hemicelluloses, pectins, lignans and lignin and the colloidal substances mainly of lipophilic extractives. They can lower the quality of the final product and cause disturbances in the papermaking process. The deposits in the systems are primarily formed of resin. The modern papermaking technology makes it necessary to use efficient retention aids. Cationic polyacrylamides (C-PAM) are common retention chemicals in papermaking. C-PAM adsorbs directly on anionic sites and forms bridges between particles. The dissolved and colloidal substances interfere with C-PAM. A high molar mass, medium charge density polyacrylamide was most effective in aggregating the colloidal substances. In the presence of fibers, the amount of resin acids was especially reduced. A cationic fixing agent and precipitated calcium carbonate used in combination with C-PAM were also effective in reducing the amount of colloidal material.