Relating MOE decrease and mass loss due to fungal decay in plywood and MDF using resonalyser and X-ray CT scanning

• Resonalyser can non-destructively measure MOE of plywood and MDF.
• Internal cracks can significantly decrease MOE of MDF.
• Cracks induce MOE decrease at incipient stage of fungal decay.
• Mass loss of single veneers of plywood is influenced by their structural properties.

Both plywood and medium density fiberboard (MDF) are often intended to be applied in conditions with fungal decay risk, which can lead to a decrease in physical and mechanical properties. It is thus essential to understand the detailed performance of the panels under fungal decay over time. In the presented research, the specimens were exposed to wet vermiculite inoculated with Pleurotus ostreatus for 14 weeks. A non-destructive flexural vibration method (resonalyser) was used to measure the Young's modulus (MOE) of the specimens, whereas the internal structure and mass loss distribution were monitored with X-ray CT scanning. The significant MOE decrease of MDF for interior use is a result of internal cracking. MDF produced with acetylated fibers showed only 1.5% mass loss and 10% MOE decrease. Plywood specimens exhibit a MOE decrease of approximately 12% at incipient fungal decay partially resulting from water dynamics and structural changes. There is a linear relationship between MOE decrease and mass loss, yet different for different types of plywood. Most mass loss occurs in the surface layers causing significant MOE decrease of entire plywood specimens, whereas the mass loss of the inner layers is influenced by structural properties of the veneers such as grain direction.