Effect of surface treatments on the durability of structural bonded timber joints

Abstract

In this study, the effects of four surface treatments (flame ionization, corona discharge, γ-glycidoxypropyltrimethoxysilane – GPMS and hydroxymethylated resorcinol – n-HMR) on three timbers (maritime pine, iroko and European oak) were evaluated through contact angle measurements (Dynamic Contact Angle Analysis using the Wilhelmy plate method) and compressive lap-shear tests involving weathered and non-weathered epoxy-bonded specimens. The wettability tests showed that both flame ionization and corona discharge treatments increased the timber’s surface free energy, with the corona leading to the greater increase, resting largely in its polar component. This treatment also tended to be less species specific, less susceptible to variation, and tended to last the longest. From the pull-off tests results, it was concluded that both flame and corona produced, at least for pine, an increase in the short-term adhesion strength that may translate into a durability enhancement for bonded joints. Once the shear tests are completed, further conclusions will be made about the effect of the treatments on the long-term bonded joint durability.