Investigating the interaction between internal structural changes and water sorption of MDF and OSB using X-ray computed tomography

Both medium density fiberboard (MDF) and oriented strand board (OSB) are increasingly used in construction, yet when exposed, water sorption can cause internal structural changes, as such decreasing mechanical strength and increasing decay risk. It is, therefore, essential to understand the interaction between structural changes and water sorption of MDF and OSB. Detailed water sorption behavior and related structural changes in two types of MDF and two types of OSB were periodically monitored using a gantry-based X-ray CT scanner. Water sorption causes local swelling in MDF, resulting in reduced swelling or even shrinkage in neighboring regions. Then again, local shrinkage can increase water resistance and possibly decrease water content locally. Obviously, local swelling results in structural changes. Such structural changes predominantly seem to appear in the transition area between high and low porosity regions. Structural changes, such as glue bonding detachment and cracking, could facilitate water intake in both MDF and OSB. For the studied T-MDF and OSB-A, the relative position of wood fibers/strands and the volume of the voids hardly changed during water sorption, which probably contributes to the decrease in water sorption along newly formed cracks and voids induced by structural changes.