Physical and mechanical characteristics of poplar treated with phosphoric acid under low-temperature thermal modification

Abstract

ABSTRACT Thermal modification can improve the dimensional stability of wood and thus expand its application. The challenge, however, lies in the approach to treating wood at low temperature, with low energy consumption and desirable performance, for a short period. Phosphoric acid was used as a catalyst to reduce the thermal-treatment temperature in this study. The effects of acid concentration and thermal treatment-temperature on the physical and mechanical properties of poplar wood were evaluated. Meanwhile, the physical and mechanical properties of acid and the thermal modification (acid-TM) of wood could be predicted based on weight loss. Results indicate that the dimensional stability of wood subjected to the acid-TM method with 0.3M phosphoric acid at 150°C for 2 h was considerably higher than that of wood treated at 210°C when their weight loss was approximately the same. The reason was that phosphoric acid hydrolyzed hemicellulose side-chains. The acid-TM process only slightly influenced the modulus of elasticity (MOE) of wood but decreased the modulus of rupture (MOR) of wood. An exponential equation can well describe the relationship between weight loss and the MOR of acid-TM wood.