STUDY ON APPLICATION OF BLOCK-COPOLYMERS COMPOSED OF POLY(VINYL ALCOHOL) AND POLYACRYLAMIDE TO PAPER SIZING

Block copolymers of poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm ) were investigated as paper additives. The mixture of both homopolyme rs in aqueous solution caused phase separation, which indicated incomp atibility. The block copolymers were soluble in water without macropha se separation. In the case of surface sizing to paper, PVA-b-PAAm as w ell as PAAm afforded stiffness to paper, whereas PVA could not. In the case of internal sizing, the block copolymers with anionically modifi ed PAAm revealed excellent improvement in paper properties, whereas PA Am made the tearing strength worse. Brittle polymers such as PAAm appe ar to afford stiffness to paper, but also make the paper brittle. PVA that is a tough polymer due to high crystallinity and low glass transi tion temperature can afford toughness to paper, at the expense of stif fness. The block copolymers seem to retain the desirable properties of each simultaneously. (C) 1995 John Wiley & Sons, Inc.