Impact of biological incising to improve phenolic resin retention and hardness of various wood species

In this study, aspen, yellow birch, and sugar maple samples were treated with four different fungi for 2, 4, and 8 weeks, for biological incising to improve wood permeability. The four fungal species were Ophiostoma piceae (wood staining fungus), Gliocladium roseum (mold fungus), Trametes versicolor, and Irpex lacteus (white-rot fungi). The fungal bio-incised wood samples and control samples not exposed to fungi were then impregnated with a low molecular weight phenol-formaldehyde (PF) resin and cured in an oven to improve wood hardness. The treated wood samples were tested for hardness according to European Standard EN 1534. Generally, bio-incising improved the PF resin uptake in wood, which improved wood hardness. The impact of bio-incising on the hardness of PF resin-treated wood samples was also related to wood species, bio-incising time, and fungi species. Microscopic examination of aspen samples treated with T. versicolor showed that fungal hyphae had moved from cell to cell through the pits. Such bio-incising behavior seems to improve wood permeability by leading PF resin to pass through the pit pairs between neighboring cells. Since the hardness of bio-incised wood samples was not always improved, the application of a bio-incising treatment to improve the hardness of resin-impregnated wood should be based on the wood species and fungal type. The bio-incising time period is also very crucial.