Thermo-hygro mechanical flattening of bamboo with intact wall structure: synergistic enhancement of mechanical properties and dimensional stability

This study developed a novel hot-pressing and humidity synergistic flattening technology that preserves the intact bamboo wall structure, addressing the issues of mechanical performance loss and poor dimensional stability caused by removing inner and outer layers in previous flattening processes while enabling synchronous drying. Through scanning electron microscopy , digital image correlation and dynamic vapor adsorption, the microstructural changes, chemical degradation mechanisms during hot-pressing, mechanical properties strengthening mechanism , and the deformation and full-field strain distribution of flattened bamboo during moisture absorption were revealed. The results demonstrated that an initial moisture content of 70 % yielded the highest flattening success rate (96 %) while enabling simultaneous drying, thereby simplifying the flattening process. The flattened bamboo exhibited significant improvements in flexural strength (207–215 MPa), flexural modulus (14.1–14.7 GPa), and compressive strength (109–112 MPa) compared to natural bamboo. Preservation of the intact bamboo wall structure reduced the external arc warpage about 70.8 % (soaking in water for one day) and lowered equilibrium moisture content through the formation of hydrophobic surfaces and reduced activity of hydrophilic groups . The thermo-hygro flattening process induced hemicellulose degradation, lignin crosslinking, and increased cellulose crystallinity , enhanced interfacial bonding , which collectively improved mechanical performance and dimensional stability. Through technological innovation and mechanism exploration, this research not only enhances the comprehensive performance of bamboo but also provides sustainable solutions for structural applications such as flooring, prefabricated housing components, and high-strength laminated composites , advancing bamboo's role in eco-friendly engineering.