The Properties of Thermo-Catalytically Prepared Wood-Polymer Composites

Gamma radiation has been used to initiate the polymerization of monomers infused in wood. Monomers with a low G value, such as styrene, are usually chosen for this process. In these studies, a thermocatalytic process was investigated using materials with properties superior to those of styrene, namely polyvinyl chloride and a copolymer, of acrylonitrile and styrene. Red pine sapwood cubes were fixed in a wire frame within a glass reactor. The monomer solution was introduced into the bottom of the reactor, and the solution was frozen by immersing the reactor in liquid nitrogen. The reactor was evacuated for 8 hours, then sealed, and the solution was melted and the reactor inverted to immerse the samples. When the reaction period was over, the glass was cooled, broken, and the samples removed and heated to remove excess monomer. Samples were tested for hardness and dimensional stability. Polyvinyl chloride was unsuitable as a monomer, Results with the copolymer of styrene and acrylonitrile were encouraging. The effect of catalysts upon the properties of the WPC products were tested with benzoyl peroxide and 2-azo-bis-isobutyronitrile. Depending on the degree of polymer loading, the volumetric swelling decreased, the weight of absorbed water decreased, and hardness increased. The azo catalyst was preferable because of the lower required concentration and the shorter reaction times. In this experiment, where wood was not swelled, the copolymer filled only the cell cavities and intercellular spaces; there was no graft copolymer present. The effectiveness of the treatment depended on the extent to which the cell cavities were filled. These results compared favorably with results from the best materials produced by radiation polymerization.

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