モクシツ ザイリョウ ノ カイリョウ ニ カンスル ケンキュウ ダイ2ホウ WOOD PLASTIC COMBINATION WPC ノ セッチャクセイ ニツイテ ソノ1 ポリマーリョウ オヨビ ヌレ ノ エイキョウ ニツイテ
Studies on the Improvement of Wooden Materials(II) : On the Gluability of Wood-Plastic Combination (WPC)(Part 1) : Effect of Polymer Content and Wettability
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In the present paper, the gluability of wood-plastic combination (WPC) with several conventional wood adhesives is investigeted.
The wood specimens used in this experiment was prepared from clear, defect-free sliced veneer of Kaba (Birch, Betula Maximowicziana REGEL ; 1.5 mm. thickness) and Hickory (Carya ovata K. KOCH ; 1.3 mm. thickness). These woods were pretreated with ethyl alcohol-benzene solution to extract away soluble materials. WPC was produced with the pre-extracted wood-methyl methacrylate-benzene-benzoyl peroxide system by means of the heat-catalyst polymerization method. Before gluing, the gluing surface of WPC was sanded with No. 80 sandpaper.
Treated wood (WPC), matched control (extracted and sanded wood) and untreated wood were glued with epoxy resin adhesive, urea resin adhesive or polyvinyl acetate emulsion, and three-ply plywoods were produced with conventional method. The tensile shear test of glue-joint was carried out on these specimens.
The wettability of the specimens was measured by the inclined plate and droplet methods with distilled water.
The results obtained were as follows :
(1) The tensile shear strength of WPC varied in an inverse manner with poly-mer content; the higher the polymer loading the lower the tensile shear strength (Figs. 1 and 2 ). This may be due to that the moisture diffusion rate in WPC is considerably slower than in untreated wood.
Also, the wood failure was hardly observed in WPC while it was high in untreated wood and control.
(2) The wettability of WPC decreased along with increased polymer content (Figs. 3 and 4 ). This may be due to the effect of non-polar polymer which deposits in WPC.
(3) The types of polymer here employed gave significant effect on the tensile shear strength and wettability. The effect of polystyrene was greater than that of polymethyl methacrylate (Table 2 ).
(4) The extraction of woods with ethyl alcohol-benzene solution gave the tensile shear strength lower than that of the untreated wood, while the wettability of these speimens was better than untreated wood. But, when the gluing surface of pre-extracted wood was sanded using a sandpaper, the tensile shear strength and wettability were generally same or larger than those of untreated wood (Table 1 ).
Shimane University, Faculty of Agriculture