Effects of Heat Treatment on the Mechanical Properties and Thermal Stability of Bamboo.

Bamboo contains abundant hydrophilic components such as hemicellulose which result in poor interfacial compatibility with epoxy resin and, consequently, limit its application in bamboo-epoxy composite packaging materials. In this study, we subjected bamboo (aged 3-4 years) to vacuum heat treatment to investigate the effects of treatment temperature (140, 160, and 180 °C) and holding time (4 and 6 h) and systematically evaluated the resulting changes in density, surface color, microstructure, mechanical behavior, and thermal stability. It was found that temperature serves as the dominant factor regulating bamboo color. With the increase in the heat treatment intensity, the lightness and yellowness of bamboo decrease, and the redness rises first and then falls, while the total color difference increases continuously. The optimal flexural strength and modulus of the treated bamboo are obtained at 140 °C, while its maximum tensile strength appears at 160 °C for 4 h. However, prolonged exposure at 180 °C causes marked mechanical degradation of the treated bamboo, which is attributed to the damaged fibrous structure. As for thermal stability, heat treatment removes heat-sensitive components, thereby increasing the 5% mass loss temperature and thermal degradation activation energy. Among all conditions, the sample treated at 160 °C for 6 h exhibits the best overall thermal stability, whereas excessive treatment at 180 °C destroys cellulose microcrystals and reduces the activation energy at high conversion rates. Considering the surface appearance, mechanical performance and thermal resistance comprehensively, the heat treatment at 140-160 °C with a 4 h holding time is the optimal modification process, which can provide theoretical and data support for the pretreatment of bamboo-based eco-friendly packaging composite materials.