Influence of incubation time on the vibration and mechanic properties of mycowood

The goal of the current study was to investigate the physical and mechanical properties of mycowood as a high quality tone-wood, obtained from Norway spruce by treatment of the white rot fungus Physisporinus vitreus as a function of the treatment time. In focus was the stiffness to weight ratio, which is often considered a main criterion for tone-wood selection. The vibro-mechanical properties were tested by non-destructive methods. The change of color and density were also measured after 4–12 months of fungal incubation. Density decreased up to 5% after 12 months of fungal treatment. Sound velocity was measured in small size specimens by means of the free-free vibration approach, while in large specimens the air-coupled ultrasound method was applied. The two techniques gave similar results and indicated that the sound velocity decreased in mycowood. Internal damping was increased in mycowood to a higher extent than the reduction in the specific modulus of elasticity (E/ρ) and thus the sound velocity in the material. The sound velocity was decreasing with increasing incubation times and scattering of data with this regard was larger in the transversal than in the longitudinal direction. The sound radiation coefficient and the characteristic impedance were enhanced in mycowood and its color was more brownish and richer in tone