Effect of Vacuum Heat Treatment on Surface Hydrophobicity and Chemical Composition of Moso Bamboo for Natural Fiber Composites

To enhance the interfacial bonding between bamboo and the polymer matrix in natural fiber composites (NFCs), vacuum heat treatment was applied to moso bamboo strips at temperatures ranging from 140 to 180 °C with holding times of 4 and 6 h. The effects of treatment conditions on the surface characteristics and chemical composition of bamboo were systematically investigated. Scanning electron microscopy (SEM), contact angle measurements, and Fourier transform infrared spectroscopy (FTIR) were employed to evaluate the changes in microstructure, surface wettability, and the main functional groups including α-cellulose, hemicellulose, and lignin. The results indicate that the severity of heat treatment (temperature–time combination) significantly influences the physicochemical properties of bamboo. Hemicellulose, which exhibited the lowest thermal stability, underwent pronounced degradation above 140 °C and showed the most substantial compositional variation. Although the relative contents of α-cellulose and lignin increased with increasing treatment severity, their absolute contents decreased. The vacuum environment was found to retard the degradation of α-cellulose to some extent. At 180 °C, severe disruption of the cell wall structure was observed, accompanied by the deformation and collapse of cell lumens. In addition, heat treatment increased the surface contact angle, indicating enhanced hydrophobicity, with temperature exerting a more pronounced effect than treatment time. FTIR analysis revealed a marked reduction in the intensity of the C=O stretching vibration of hemicellulose (~1730 cm−1) and the O–H stretching vibration (~3400 cm−1), while the aromatic structure of lignin remained relatively stable. Overall, vacuum heat treatment effectively enhanced the surface hydrophobicity of bamboo, providing a theoretical basis and technical support for the development of bamboo-reinforced natural fiber composites.