Strength grading of Chinese poplar wood for structural use following thermal modification

Abstract

Thermal modification has been commonly perceived to improve wood dimensional stability, but decreases certain main mechanical properties. This research aimed to optimize thermal modification for poplar wood to determine its impacts on strength class for potential structural use. In this study, poplar wood was thermally modified at temperatures between 160 and 210 °C and 2 h duration, after which the chemical composition and mechanical properties were determined. The results showed thermal modification led to hemicelluloses degradation, which served as the main reason for strength reduction. The main mechanical properties of thermally-modified wood decreased with temperatures, except for compressive strength and modulus of elasticity, which increased with temperature (≤180 °C) and was followed by a reduction at ≥190 °C. The strength class of thermally-modified wood was dependent on the smaller value of modulus of elasticity and shear strength. Thermal modification at 180 °C was shown to be practical in improving wood properties for structural use.