ALKALINE SIZING WITH ALKYLKETENE DIMERS IN THE PRESENCE OF CHITOSAN SALTS

The effects of addition of aqueous chitosan solutions to pulp suspensi ons subject to alkylketene dimers (AKD) sizing in alkaline papermaking were studied with chitosan hydroacetate, chitosan hydrochloride and w ater-soluble chitin. Sizing degrees, AKD and filler contents of the ha ndsheets were measured, and compared with those of AKD-sized handsheet s prepared with polyamideamine-epichlorohydrin resin (PAE). The chitos an hydroacetate gave the largest effect on sizing and AKD retention am ong the polymers used at 0.1-0.4% addition levels. Good correlation be tween the AKD content and the degree of sizing was obtained for most o f the handsheets prepared. Since chirosan forms colloidal particles in alkaline solutions, this polymer probably precipitates on anionic sit es of amphoteric AKD emulsion particles immediately after its addition . The increase in cationic surface charges of AKD emulsion particles b y chitosan molecules may therefore, have resulted in the higher retent ion of AKD.