Preparation of cationic sulphite pulp and its effect on strength properties and filler retention

Rendering cellulose fibres cationic via in-situ polymerization has been regarded as one of the effective approaches to enhance paper strength and filler retention. In this work, the preparation of cationic pulps by the in-situ grafting of acrylamide and cationic monomer, [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride, was investigated systematically. Efforts have been undertaken to optimize the grafting conditions for the free-radical copolymerization. The kinetics of the polymerization were also explored The resulting cationic pulps in conjunction with the unmodified pulps led to a significant increase in the tensile strength of the handsheets prepared, although the tear strength deteriorated at the same time. The presence of cationic pulps (5 wt%) in the pulp suspension improved clay filler retention; the retention effect was improved further by the synergy between cationic pulps and a conventional cationic polymer added at an extremely low dose. Moreover, the improved filler distribution along fibre surfaces was achieved by the addition of cationic pulps, as observed by both optical and scanning electron microscope.