Effects of steam treatment on bending properties and chemical composition of moso bamboo (Phyllostachys pubescens)
Effects of temperature (25, 160 and 200 °C) and time (15 and 30 min) of steam treatment on the mechanical and chemical characteristics of moso bamboo were studied. The modulus of rupture (MOR) and modulus of elasticity (MOE) of the outer culm were at least 2.4 and 2.2 times respectively greater than those of the inner culm. Temperature and time had no effect on bending properties of the outer and inner culms. A significant decrease in MOR occurred after the specimens were subjected to 200 °C. The per cent MOR reduction after 30 min treatment at 200 °C was more than 33 and 29% respectively, as compared with that of 25 and 160 °C, but steam treatment had no effect on MOE. Of the three major chemical constituents of bamboo, alpha-cellulose was very stable to temperature and time, but lignin content increased slightly when temperature was increased to 200 °C. However, the hemicellulose content decreased substantially as temperature increased. The similar decreases for hemicellulose content and MOR of bamboo suggested that hemicellulose loss in thermally- degraded bamboo was correlated with MOR strength loss. At 200 °C, there were significant decreases in MOR, hemicellulose content and pH, and increases in hot water extractives, ethanol–benzene extractives, 1% NaOH extractives and lignin content.