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/mm2) and wood failure (%) after exposure to soaking in different buffered solutions (pH = 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 4- and 7-mo exposures to acidic conditions but did not change significantly under alkaline exposures. However, the buffered acidic solutions (pH = 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