Investigating water transport in MDF and OSB using a gantry-based X-ray CT scanning system

Both medium density fiberboard (MDF) and oriented strand board (OSB) are important engineered wood products. Water uptake can decrease their physical and mechanical properties as well as induce fungal decay. It is therefore essential to understand the water transport behavior in these products in detail. In this research, a state-of-the-art gantry-based X-ray CT scanner was used to investigate the water transport and the internal microstructure of the specimens from different types of MDF and OSB during water uptake. The results show that water, obviously, is mainly absorbed from the sides of all specimens during immersion testing. Water can reach the interior of the small specimens within 1 h through large fibers and strands. Although water movement through voids is slow, high water content can be reached when these voids are filled; for example, moisture content of more than 100 % is found in MDF. A compact structure can effectively decrease water accumulation in voids. Furthermore, the presence of a water-resistant adhesive, a water-repellent additive and acetylated fibers clearly influences water transport behavior in wood fibers and voids, increasing water resistance and improve structural stability of MDF. Moisture dynamics of OSB are different, among others influenced by orientation of the strands: grain direction perpendicular to the water uptake direction can protect OSB from water penetration. Furthermore, strands covered with resin have a good water resistance.