Glueline Characteristics and Bond Durability of Southeast Asian Species After Solvent Extraction and Planing of Veneers

Bond durability and microscopic characteristics of gluelines were studied in plywood made with veneers of nine species of Southeast Asian woods. Veneers were either planed, extracted with a 1 percent caustic solution, or left untreated before gluing. Wood failure was tested in a split-plot experimental design, including four replications of each of the veneer treatments. Other variables were two phenolic adhesives, assembly times of 20 and 45 minutes, and aging methods by vacuum-pressure soak (VPS) and automatic boil. Douglas-fir veneers were used for the cores in the three-ply panels and as a control species for the study. Veneer surfaces and plywood glue-lines were observed microscopically for anatomical structure, resin distribution, and uniformity. Wood failure for untreated veneers of five species averaged below the acceptable level of 85 percent for exterior use, but all species exceeded this level when veneers were planed before gluing. Solvent extraction of the veneer surfaces did not improve bond durability. Planing appeared to produce uniform glueline thickness and adhesive distribution, as well as exposing new wood surfaces for adhesive contact. Type of adhesive, assembly time, and aging method did not cause any practical significant differences in results of this study.

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