Surface activation of wood by corona treatment and NaOH soaking for improved bond performance in plywood

In plywood manufacturing, the surface characteristics of veneers play a critical role in achieving appropriate bonding performance. An inactivated wood surface caused by oxidation or migration of wood extractives has been shown to lead to an insufficient bonding quality. In this study, inactivated birch and spruce veneer surfaces were activated with corona and chemical NaOH treatments. The effects of the treatments were determined by contact angle measurements and bond quality tests conducted with Automated Bonding Evaluation System (ABES). In addition, the mechanical properties of the plywood produced from the treated veneers were evaluated. The results showed that the corona treatment remarkably increased the wettability of the veneer surface and bond quality of both the spruce and birch veneers evaluated by ABES. The corona treatment also improved the mechanical properties of the birch plywood, but the spruce plywood properties were not affected as much. Soaking veneers in NaOH improved the wettability, but the bond strength was lower than that of the references.