Starch Xanthide in Handsheets and Machine-Made Papers

Starch xanthide, an internal adhesive for paper, imparts high levels of wet strength along with improved dry strength. Laboratory quantities of starch xanthide, degree of substitution of 0.12, were prepared and used in handsheets to evaluate incorporation procedures. The quality of these handsheets was compared with that of machine-made papers containing starch xanthide formed by a continuous process. Results showed that starch xanthide should be produced as a disperse system of insoluble particles and that large coagulated particles are less effective than small ones in changing the properties of paper. Rapid blending of starch xanthate and acidified sodium hypochlorite crosslinking reagent improves the performance of the resulting starch xanthide dispersions and reduces the amount of oxidant needed. Starch xanthide dispersions at a concentration of 0.125 %, to avoid premature coagulation, are best added after alum has been blended with pulp fibers. Up to 10 % starch xanthide was incorporated in handsheets made from a number of pulps.