synopsisThe effect of radiation dose rate and beating time on the mutual radiation grafting of styrene to unbleached and bleached h a f t wood pulp was studied. Companion studies on the effect of beating time, peroxidation grafting, and order of monomer addition on the preirradiation graft copolymerization of acrylamide and diethylaminoethyl methacrylate were conducted on bleached wood pulp. The grafting rate of styrene increased with dose rate, but the kinetics suggests a significant diffusional resistance to the observed grafting rate. The per cent graft measured a t fixed grafting conditions decreased markedly as pulp beating (effected prior to grafting) was increased. It is suggested that the decrease in grafting with beating is due to an increase in the accessibility and swelling of the beaten fibers. Dimethylaminoethyl methacrylate appeared to inhibit the grafting of acrylamide, and double grafting had to be used to graft both hydrophilic polymers to the pulp. The mechanical properties of high-yield pulp and groundwood were improved by the addition of the grafted pulps. The double grafts appeared to show promise as fibrous beaten additives for dry strength improvement. The styrenegrafted pulps were found not to respond a t all to the beating process.
INTRODUCTIONGraft polymerization onto cellulose and its derivatives has been investigated in great detail. An excellent and complete review of the whole field of grafting onto polysaccharides has recently been published by Arthur.' Grafting to wood pulp has been less studied than to purer forms of cellulose but has received increasing attention in recent years in attempts to improve the properties of paper by this technique. A review of this work has recently been presented by Phillips et a1.2 Earlier studies in these laboratories with the radiation grafting of ~t y r e n e~-~ and with acrylamide6 have now been extended to another monomer, N-dimethylaminoethyl methacrylate, and to its copolymers with acrylamide and to double grafts with both homopolymers. Acrylamide was chosen because it is known to improve the strength of pape+ through its high hydrogen-bonding capacity. With high-yield pulps and with groundwood, however, it is not so e f f e c t i~e ,~ It was thought that a cationic polymer such as N-dimethylaminoethyl methacrylate might provide a better partial ionic bonding with the ligno-sulfonates and other lignin moieties in the wood pulp. Such a possibility has been
RADI, HOPFENBERG, AND STANNETTdiscussed in detail by Linke' for the case of polymeric dry-strength additives for papers. Combinations of both monomers could therefore in principle lead to excellent dry-strength properties, even with high-yield pulps.In addition to studies of the new monomer system, the specific effect of beating has been investigated in some detail. Beating is a mechanical treatment of wood pulp used routinely in the paper industry which defibrillates, masticates, and severs the pulp fibers. This seemingly straightforward process is, in fact, highly complex and results in d...
