Mechanical properties of adhesives for bonding wood—A review

In this review the current state of the art on mechanical properties of pure wood adhesives is summarised and discussed. Conventionally, mechanical adhesive properties were characterised by means of macroscopic tensile or bending tests of ex-situ cured adhesive films. More recently, nanoindentation was also used to characterise such ex-situ specimens, but more importantly, this method allows the mechanical characterisation of adhesive bond lines in-situ. Mechanical tests reveal high variability between, but notably also within specific groups of adhesives. For example, the modulus of elasticity covers a wide range of more than two magnitudes ranging from 0.1 GPa up to 15 GPa. Significant differences in adhesive stiffness were observed for adhesives intended to be used for solid wood products compared to wood based composite adhesives, the latter showing higher modulus values. In addition to mechanical adhesive properties as such, factors possibly influencing adhesive performance such as temperature, humidity or ageing of the bonds are taken into consideration.