Comparison of microscopy and quality control testing to examine the durability of adhesive bondline in cross-laminated timber

Adhesive bonding quality significantly contributes to the integrity and quality of cross-laminated timber (CLT). There are several factors affecting bonding quality in glued-layered wood products such as CLT that are generally categorized as the properties of wood, adhesive type and curing conditions. The adhesive bonding performance of five different types of CLTs made from yellow-poplar and southern pine lumber using phenol-resorcinol formaldehyde and polyurethane structural adhesives were studied using light microscopy and ANSI/APA PRG-320 mechanical evaluation tests. The results show that CLTs with a thin bondline and the highest effective penetration had the highest shear strength, and with least face delamination. The effect of wood anatomy on bonding quality was demonstrated in mixed species CLT with different penetrations into different species. The effect of adhesive curing was observed through the presence of generating gaps and microbubbles in adhesive lines.