Multi-scale characterization of the effect of saturated steam on the macroscale properties and surface changes of moso bamboo

Bamboo is a woody material that has become a key substitute for wood resources in many fields. This study is aimed to analyze the effects of saturated steam (140, 160, 180 °C) on physical, crystallinity, chemical composition, mechanical properties as well as microstructures at different periods (4, 6, 8, 10 min). Expectedly, a reduction of hemicellulose and cellulose and increment of relative content of lignin in bamboo when temperature above 160 °C was positive to reduce the equilibrium moisture content (EMC). Thus, the hygroscopicity improved and the parenchyma cells and vascular bundles were shrunk slightly. Both temperature and time positively affected the crystallinity of bamboo samples in comparison with the control. Heat treatment parameters affect the mechanical properties of bamboo. When the treatment was carried out at 140 °C, the modulus of rupture (MOR) and modulus of elastic (MOE) increased in comparison to no treatment; Furthermore, The MOR and MOE decreased by 40% and 19% compared with that of the untreated bamboo at 180 °C for 10 min. The temperature and time had a great influence on a*, b*, and L* of the bamboo. The results showed that during the heat treatment, the bamboo color changed from light yellow to dark red-brown, and the overall color changed evenly. Among them, a* increased firstly and then decreased, indicating that the treated bamboo was reddish, while b* and L* mainly showed a downward trend. The ΔE value positively corresponded to heat treatment severity.