Molecular-Level Characterization of Changes in the Mechanical Properties of Wood in Response to Thermal Treatment

Abstract Thermal treatment can improve the dimensional stability of wood, but it also decreases wood’s stiffness and increases its brittleness. In this paper, combining FTIR spectroscopy and mechanical analysis was used to in-situ study the molecular-level responses to stresses and analyze mechanical interactions among components in thermally-treated wood. For both untreated and treated woods, the cellulose was the longitudinal tensile load-bearing component of wood, but the lignin participated in the load transfer in the fiber direction. Moreover, the FTIR results indicated that hemicellulose degradation, as the interface between cellulose and lignin, decreased shear slipping between microfibrils. The interfacial material degradation also caused the wood’s stiffness and mechanical responses of the matrix along the cell transverse direction decrease. Upon increasing the heat treatment intensity, the cellulose microfibrils rearranged along the cell axis, resulting in the ability of the cell wall to resist deformation and the wood’s stiffness being increased.