Chemical analysis of industrial-scale hydrothermal wood degraded by wood-rotting basidiomycetes and its action mechanisms

Abstract

The hydrothermal treatment has been developed as an industrial method to enhance the biological durability and dimensional stability of wood. The resistance against wood-rotting fungi of Pinus radiata and Fraxinus excelsior industrially-heat treated at 210 °C was evaluated inoculating Trametes versicolor and Gloeophyllum trabeum according to standards and comparing with untreated samples after 8-and 24-weeks incubation. Furthermore, wet and instrumental chemical analyses were carried out to quantify changes in chemical composition and to analyze fungal degradation mechanisms. The results showed enhanced durability against wood-rotting fungi in industrial hydrothermal wood at 8 weeks of exposition (Durability Class = 1; MC = ≤6%). However, the moisture content increased over time (MC = 9–10%) favoring a gradual oxidative degradation and allowing an enzymatic action with higher mass losses (up to 10% after 24 weeks). Moreover, it was confirmed that industrial hydrothermal wood interacts as a crosslinking network where polysaccharides are less available to rotting fungi, but low molecular weight fragments released such as the phenolic compounds could be merged into the lignin fraction, producing a relative amount of nutrients vulnerable to degradation as shown in the decrease of the lignin content and in the elevated depolymerization degree after fungal exposure.