EFFECTS OF pH ON LAP-SHEAR STRENGTH FOR ASPEN VENEER

This study is one part of a whole project called “Impact of Extreme pH of Structural Adhesives on Bond Durability.” The objective of this study was to evaluate effects of pH on wood– adhesive bond strength and chemical change in aspen (Populus tremuloides Michx) wood caused by extreme pH exposures. Aspen veneer lap-shear samples were tested for maximum stress (N/mm) and wood failure (%) after exposure to soaking in different buffered solutions (pH 1⁄4 2.0, 2.5, 3.0; water, 10.0, 11.0, 11.5, 12.0, and 12.5) for 1, 4, and 7 mo. One set of samples stored in laboratory conditions was also tested as a control at each test time. Results indicated that bond strength and wood failure decreased after 4and 7-mo exposures to acidic conditions but did not change significantly under alkaline exposures. However, the buffered acidic solutions (pH 1⁄4 2.0 and 3.0) did not cause a measurable chemical change in aspen wood, whereas losses in hemicellulose and lignin were found after aspen wood specimens had been exposed to pH > 11.0 buffered solutions.