Evaluation of timber adhesion promotion techniques for solid timber substrates

Abstract

Long-term durability of a structural adhesive joint is an important requirement, as it has to be able to support the required design loads, under service conditions, for the planed life time of the structure. One way of improving bond durability is through the use of surface treatments prior to bonding. In this study, the effects of four surface pre-treatments on three timbers were evaluated quantitatively through contact angle measurements and shear tests. The wettability tests showed that both flame and corona techniques 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. The shear tests, which are still ongoing, showed nevertheless that, in some cases surface activation, by itself, may not be sufficient to produce durable joints. Thus in such situations, it is also necessary to dimensionally stabilize the bond line, so as to enable it to cope with the timber dimensional variations originating from moisture ingress/egress.