In an attempt to evaluate the effects of thermal treatment on wood cell walls (CWs), Masson pine (Pinus massoniana Lamb.) wood was thermally modified (TM) at 150, 170 and 190°C for 2, 4 and 6 h, respectively. The chemical properties, cellulose crystallinity (C _rI) and micromechanics of the control and thermally modified wood (TMW) were analyzed by wet chemical analysis, X-ray diffraction and nanoindentation. The relative lignin content and C _rI increased after the TM partly degraded the amorphous wood polymers. The relative lignin content was higher in TMW and the equilibrium moisture content decreased. Moreover, the elastic modulus (E _r) and hardness (H) of TMW were lowered along with the creep ratio decrement (C _IT) of CWs. However, a severe treatment (e.g. 190°C/6 h) may negatively affect the mechanical properties of CWs caused by the partial degradation of hemicelluloses and also cellulose.

Atomic force microscope infrared spectroscopy (AFM-IR), contact resonance AFM (CR-AFM) measurement, and nanoindentation were combined to identify the interactions between wood cell wall and phenol-formaldehyde resin (PF) on the nanoscale.

A combination of compression and heat treatment is a modification method that has great potential for improving the mechanical properties and dimensional stability of wood materials in industrial application. The objective of this project was to track changes in the microstructure, chemical composition, cellulose crystallinity, and mechanical properties of the treated poplar cell wall to investigate the mechanism of modification. Poplar boards were compressed at 100°C and subsequently treated in the hot press at 200°C. The results indicated that the treatment contributed to a reduction in porosity without obvious mechanical compression and damage to the cell wall. Hemicellulose degraded, however, and the relative lignin content and cellulose crystallinity increased during the process. The observed increase in relative lignin content and crystallinity may contribute to the improvement of mechanical properties. The longitudinal elastic modulus and hardness of poplar cell walls increased significantly from 12.5 and 0.39 GPa for the control to a maximum of 15.7 and 0.51 GPa for compressed wood with HT, respectively.