Cell Wall Polymer Degradation during Rhodonia placenta Brown Rot Decay of Thermally Modified and Unmodified Wood

Thermal modification produces decay-resistant wood suitable for sustainable applications. Although thermally modified wood remains degradable by fungi, its degradation mechanisms are poorly understood, impacting long-term eco-friendly use. This study investigated thermally modified wood degradation by elucidating chemical changes to wood cell wall polymers during Rhodonia placenta brown rot decay. Modified and unmodified Scots pine samples were exposed to R. placenta in stacked-sample decay tests, generating decay stage progressions. Decayed samples were analyzed by near-infrared spectroscopy with multivariate analysis to identify key chemical changes. Milled wood lignin was isolated and analyzed by two-dimensional nuclear magnetic resonance spectroscopy for further lignin chemistry insight. Results showed that R. placenta degraded thermally modified wood to high mass losses. Chemical changes were characterized by carbohydrate degradation and oxidative lignin modification, typical for brown rot. While most degradative changes were similar between modified and unmodified wood, differences in lignin modification patterns were observed. Interestingly, spectroscopic data revealed different chemical changes in the early and late decay stages in modified and unmodified wood. These findings highlight the time-dependent nature of R. placenta degradation and show that thermally modified and unmodified woods are degraded by similar yet different mechanisms, providing new insight into brown rot wood degradation.