GRAFT-COPOLYMERIZATION ONTO WOOD FIBERS - OZONE-ACTIVATED HYDROPHOBIZATION OF PRETREATED WOOD PULP

Despite the fact that graft copolymerization is a favored reaction for cellulose xanthate, a significant part of the cellulose and lignin co mponent is subject to undesired degradation reaction. Exposure of ther momechanical pulp to ozone followed by grafting by the xanthation meth od further degrades the cellulose and decreases graft yield. Graft yie ld can be improved by introducing chemical crosslinks to the cellulose backbone before or after ozone exposure. It is suggested that crossli nking with formaldehyde recombines some of the degraded chains of hydr oxylated cellulose after ozone exposure and also helps to prevent degr adation of cellulose chain during grafting of cellulose xanthate. Sizi ng of pulp with dispersed and saponified rosin-Al complexes slows down the grafting reaction and decreases the polymer add-on percentage sig nificantly. An exposure to ozone before or after the sizing process im proves grafting efficiency and graft yield and the copolymer formation is the preferred reaction. The surface morphology of sized pulp has p ractically no influence on the grafting parameters. Unlike the sizing mechanism, the chemical nature of the sizing agent influences the graf ting process. Sizing of pulp with an alkyl ketene dimer significantly decreased the copolymer formation by preventing reactive cellulose hyd roxyl group from reacting.