Understanding the mechanical strength and dynamic structural changes of wood-based products using X-ray computed tomography

The mechanical strength of wood-based products (WBP) is determined by the anatomical structure of wood, including the specificities of earlywood (EW) and latewood (LW), and the bonding interphase between wood and adhesive. In this study, two-layered specimens were manufactured according to three possible assembling strategies in terms of the anatomical structure of wood. Wood micro-structure and phenol formaldehyde (PF) adhesive distribution were visualized with optical and fluorescence microscopy. Internal structure changes were dynamically monitored using X-ray computed micro-tomography (X-ray mu CT) while compressing specimens. The results showed that in EW, adhesive could penetrate into cell lumens through collapsed cell walls. In LW, an adhesive can diffuse along rays. In bonding interphase, consisting of EW and LW, an adhesive preferably penetrates into EW. The adhesive increases EW stiffness but has little impact on the stiffness of LW.EW was mainly compressed during compression due to the collapse of the thinner cell walls and larger lumina. The collapse of the cell walls was more likely to happen in regions close and parallel to the boundary of growth rings. The cell structure in adjacent areas to resin ducts of LW was more affected, as these can be squeezed under compression.