Effect of thermo-mechanical treatment with different initial moisture content on bamboo cell walls

Thermo-hydro-mechanical (THM) treatment is an effective way to improve the performance of bamboo. However, to date, research on the impact of moisture content (MC) on THM treatment has been relatively little. This study examined the microstructure and physical and chemical properties of bamboo treated with THM under different initial moisture content conditions. The interaction and influencing relationships among the three were explored to provide a reference for THM in the bamboo industry. According to the results of the Three-point Bending test and Nanoindentation test, it is indicated that humidity has a relatively minor impact on the mechanical performance and micro-mechanical properties of compressed samples. However, Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimetry (MIP) tests have shown that an increase in moisture content effectively improves the uneven deformation of bamboo cell walls during compression, thereby reducing their porosity. However, appropriate moisture content in the experiment affected the softening effect of bamboo and caused slight cracking of the fiber tube during compression. With respect to Fourier Transform Infrared Spectrometer (FTIR) spectroscopy, differences in the initial moisture content can also affect the chemical composition. The X-ray diffraction (XRD) analysis has also shown that the crystallinity of the treated samples was higher than that of the untreated samples. Moisture content has a significant impact on the hygroscopicity and dimensional stability of compressed samples by influencing changes in the chemical composition, microstructure, and crystallinity during thermo-hydro-mechanical treatments. In this experiment, bamboo with a moisture content of 12% had a pronounced softening effect during the hot-pressing process while exhibiting the dimensional stability and low moisture absorption required.