Preparation and application of cationic cellulose fibers modified by in situ grafting of cationic PVA

Rendering the cellulose fiber cationic via in situ graft copolymerization has been regarded as one of the effective approaches to improve the filler retention and distribution. In this work, cationic cellulose fibers were prepared by in situ copolymerization of vinyl acetate (VAc) and diallyldimethyl ammonium chloride (DADMAC) onto softwood sulphite pulp fibers using ceric ammonium nitrate (CAN) as a free radical initiator, followed by alkaline hydrolysis. Effects of various process parameters were systematically investigated, such as temperature, reaction time, initiator concentration, etc. Fourier transform infrared spectroscopy (FT-IR) was performed to confirm the existence of the grafted copolymers on the surface of sulphite pulps. The charge density of modified fibers was determined via back titration using a Particle Charge Detector MÜtek PCD 03. The difference between grafted fibers and virgin fibers was also revealed by the SEM observation. The resulting cationic pulps led to significant improvement of filler retention and distribution. Further improvement in filler retention was achieved by the synergy between cationic pulps and a conventional cationic polymer. In addition, the improved distribution of filler along fiber surfaces achieved by the addition of cationic pulp was demonstrated by both optical microscope and SEM observation.