Impregnation of Wood with Vinyl Monomers

White pine and loblolly pine sapwoods were impregnated with methyl methacrylate inhibited with 35 parts per million of butylated hydroxytoluene. The monomer was polymerized by gamma irradiation from cobalt-60 at a dose rate of 0.22 Megarad per hour to a total dose of 5.0 Megarads. Variations in treating techniques resulted in variation in the amount of monomer forced into the wood and distribution within a single piece. Since there was very little variation in density in the wood used, density variation measured by the beta-ray technique was assumed to be variation in monometer. Full cell treatment or a vacuum-pressure treatment gave monomer loads very close to theoretical maximum loads. Short soak times under atmospheric pressure were not satisfactory for uniform partial loading. Capillary redistribution times of from 1-3 days appeared to be most effective in leveling off monomer distribution gradients. A light final vacuum after draining monomer did initially reduce the high end loadings. For partial treatments of approximately 80 percent of maximum values, a Lowry type treating process gave best results insofar as uniformity was concerned, but loading control with this process was difficult. For lesser loading percentages the following cycle gave the least variability: empirically selecting a partial vacuum and maintaining it for 20 minutes and then introducing the monomer into the treating cylinder while maintaining a partial vacuum. Then the samples were soaked at atmospheric pressure for 4 hours, drained, and nitrogen pressure of 125 psi applied for 18 hours. The pressure was then released over 1-1/2 hours. A relatively uniform high surface loading with low core loading was obtained using a modified Rueping type treating process.

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