Effects of fungal exposure on air and liquid permeability of nanosilver- and nanozincoxide-impregnated Paulownia wood

• Permeability is low in Paulownia wood due to the existence of tyloses.
• Permeability increases by impregnation process as a result of the breakage of tyloses.
• Impregnation with zinc-oxide nano-suspension decreases the fungal growth.

Effects of aqueous dispersion of silver and zinc-oxide nano-particles on air and liquid permeability of Paulownia wood exposed to Trametes versicolor were studied in the present research project. Specimens were also heat-treated at 100 and 150 °C and compared with the control specimens. Permeability values were measured when the moisture content of the specimens was 12%. Results showed significant increase in air permeability after impregnation with either nanosilver or nanozinc. The increase in permeability was due to the breakage of tyloses under the high pressure in the impregnation vessel. However, significant decreases were observed in permeability in all treatments after the fungal exposure. The decrease was related to the growth and accumulation of hyphae along vessel lumens, blocking the path for fluid transfer. It was concluded that both heat-treatment at 150 °C and the impregnation with zinc-oxide significantly inhibited growth of the fungus, consequently decreasing wood mass loss. High and significant correlations were observed between air and liquid permeability only in specimens that were impregnated with either of the nano-suspensions.