木質材料の改良に関する研究(第3報) : Wood-Plastic Combination(WPC)の接着性について(その2) : ポリマー量およびオープンアセンブリータイムの影響

The wettability of wood-plastic combination (WPC) is worse than that of untreated wood. This wettability depends strongly on the polymer content. For that, it may be difficult that WPC is glued with conventional wood gluing technique. In the present paper, the effect of open assembly time and polymer content on the gluability is investigated using several conventional adhesives.
The wood specimen used in this experiment was prepared from clear, defect-free sliced veneer of Kaba (Birch, Betula Maximowicziana REGEL : 1.5mm thickness, 15% moisture content). The specimens were extracted with ethanol-benzene solution to extract soluble materials. WPC was produced with the wood-methyl methacrylatebenzene-benzoyl peroxide system by means of the heat-catalyst polymerization method. Before gluing, the gluing surface was sanded.
The three-ply plywoods were made from treated wood or control (extracted and sanded-wood) with urea-formaldehyde resin adhesive (UF), resorcinol-formaldehyde resin adhesive (RF), epoxy resin adhesive (Epoxy) and polyvinyl acetate emulsion (PVAc) by the gluing condition shown in Table 1. After these plywood had been stored in a conditioning chamber held at 20℃ and 60% R. H. for 1 week, the tensile shear specimens were tested in a universal testing machine according to the Japan Agriculture Standard Specification.
An analysis of variance for the polymer content and open assembly time was made separately on each adhesive. The analysis of variance is shown in Table 2.
The results obtained were as follows ;
1) For all adhesives used in this experiment, the 1% level of significance was indicated on the polymer content (Table 2). For UF.RF and Epoxy,the tensile shear strength of the glue-joint decreased along with increased polymer content : UF gave especially inferior results (Figs. 1, 2 and 3). For PVAc, the tensile shear strength of the gluejoint generally increaed with the increasing of the polymer content (Figs. 4 and 5).
2) For RF and PVAC (cold-press), the tensile shear strength of the glue-joint decreased with the increasing of the open assembly time at the 1% level of significance (Table 2, Figs. 2 and 4).
3) For Epoxy and PVAc, the interraction of the polymer content and open assembly time indicated significance at the 1% level (Table 2, Figs. 3, 4 and 5).
4) The wood failure for control was almost 100%. On the other hand, that for WPC was very low (zero or nearly so) but 30 to 50% wood failure was observed for RF and PAVc (hot-press).