In a series of investigations on the improvement of wooden materials, the effects of solvent on the dimensional stabilization of wood-plastic combination (WPC) have been studied in this paper.
The wood specimens (10(R) × 50(T) × 5(L) mm) used in this experiment were prepared from sapwood and heartwood of Hinoki (Chamaecyparis obtusa ENDL.). These woods were pre-treated with ethanol-benzene solution to extract soluble materials. The solution of methyl methacrylate (MMA) -solvent-benzoyl peroxide system was impregnated into the wood under vacuum (20-30mmHg). Benzene, methanol and dioxane were selected as solvents and the mixing ratio of MMA to solvent is shown in Table 1. After soaking in the solution under atmospheric pressure for 24 hours, the impregnated woods were wrapped in aluminium foil and placed in an oven at 70℃ for 24 hours to polymerize MMA.
The hygroscopicity experiment was done in a desiccator into which a saturated solution of potassium nitrate was put, and the antiswelling efficiency (ASE) and the moisture-excluding efficiency (MEE), respectively, were caluculated from the dimensional change in tangential direction and the moisture content when in equilibrium with 20℃ and 90% relative humidity.
The results obtained are as follows :
(1) The effect of solvent on ASE becomes better in the order, methanol, benzene, dioxane (Fig. 1). Dioxane and benzene especially have a very good effect on ASE.
(2) ASE is nearly proportional to polymer content on each of 25% (Wt) and 50% (Wt) of solvents (Fig.1). In the same system, polymer content could be yielded much more at 50% (Wt.) of solvents than 25% (Wt.) but a remarkable difference in ASE between both was not recognizable.
(3) The bulking effect (increase in vacuum-dry dimension on polymerization) becomes better in the order, 25%, 50% on weight of solvents and benzene, methanol, dioxane on solvents (Fig. 2 and Table 2). The bulking effect is in inverse proportion to polymer content (Fig. 3).
(4) ASE is directly proportional to MEE (Fig. 4.). The effect of solvent on MEE becomes better in the order, methanol, benzene, dioxane. It was noteworthy that moisture content was very low when using dioxane.
(5) The relation between moisture content and polymer content is in inverse proportion on each of 25% (Wt.) and 50% ( Wt.) of solvents (Figs. 5 and 6). In the same solvent system it would seem to have no relation to either.