Moisture Sorption And Swelling Of Wood-Polymer Composites
Keywords:Monomer, polymer, wood-polymer composites, maple, red oak, southern pine, dimensional stability, swelling, acrylate, methacrylate
AbstractChanging moisture content in wood can result in dimensional changes that create problems in some circumstances. The swelling of wood by moisture is not reduced by treating the wood with monomers, resins, or polymers unless these substances penetrate the cell walls. In this study maple, red oak, and southern pine specimens were saturated with acrylic and methacrylic monomers in an effort to penetrate the cell walls with monomers. The volumes of the saturated specimens were measured after each of three soak cycles. The swelling resulting from soaking the specimens in monomers was measured. Soaking at 105 C in certain monomers resulted in a range of swelling from 2 to 21% depending on the specific monomer and species of wood. Other monomers generally did not penetrate the cell walls sufficiently to result in swelling of the wood. After the final soak period, a free radical initiator was added and the monomers were polymerized in the wood to make wood-polymer composites. The moisture content and volumetric swelling of the wood-polymer composites at 90% relative humidity were measured. The wood-polymer composites were swelled by moisture at a slower rate than was just wood, but many wood-polymer composites eventually swelled as much as did untreated wood. Some polymers were hygroscopic, which increased the moisture content and volumetric swelling of the wood-polymer composite specimens at 90% relative humidity.
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