A model to explain microscopic mechanism of hygrothermal recovery in tension wood G-fiber

In the present study, a theoretical model was developed to elucidate the microscopic mechanism of hygrothermal recovery (HTR) in gelatinous fibers (G-fibers) of tension wood (TW) from the perspective of reaction kinetics. Yamamoto et al. (2022) proposed a hypothetical mechanism to explain the origin of HTR behavior in G-fibers, suggesting that two modes of denaturation of matrix components—namely, softening and degradation of non-crystalline polysaccharides in the G-layer—cause contractile recovery of the stretched cellulose microfibrils (CMFs). However, this mechanism remains qualitative and cannot quantitatively predict the complex HTR-strain behavior observed in G-fibers, such as the “initial recovery” and “continuous contraction” reported by Sujan et al. (2015). To address this limitation, the present study employed a numerical simulation approach based on a theoretical model. First, a mathematical rule was extracted from observed temperature- and time-dependent patterns of HTR-strain in the G-fibers. Second, the softening and degradation of non-crystalline polysaccharides in the G-layer matrix, as hypothesized by Yamamoto et al. (2022), were formulated within the framework of reaction kinetics. Third, by integrating this formulated mechanism with the extracted mathematical rule, a predictive model for HTR- behavior in G-fibers was developed. Finally, the newly developed model was used to quantitatively simulate experimental results. This model facilitates a rational elucidation of the microscopic mechanism of HTR in G-fibers by representing the dynamics of cell wall components and reproducing the macroscopic HTR-behavior observed in the G-fibers of TW.