Graft Pulping in Organosolv Systems

It has been previously demonstrated that free radicals are produced in the delignification of wood. These free radicals can be utilized to initiate grafting of vinyl polymers to the wood pulp. This simultaneous delignification and graft copolymerization has been referred to as graft pulping. The grafting of a variety of vinyl monomers to aspen wood pulp in alcohol-based solvent pulping has been evaluated in this study. Variables evaluated included cooking conditions, catalysts and two-stage pulping. The analysis of the reaction is complicated due to effects of the vinyl monomers on the delignification process and losses of wood during the extraction sequences. Although only low levels of polymer loading were obtained when single monomers were added to the pulping solvent, much better results were obtained using a binary monomer system of acrylonitrile(AN) and styrene(ST). At a monomer addition level of 10% (1.75% AN, 8.25% ST) to the aqueous ethanol solvent, a 14.6% polymer loading was achieved with the majority of the graft as polystyrene (88%). The use of a two-stage pulping sequence improved the polymer loading of polyacrylonitrile but not polystyrene. Lignin was the primary site of grafting.