Relationship between lignin gradient evolution of microstructure and micromechanics of bamboo cell wall under heat regulation

Six-year-old moso bamboo was subjected to high-power microwave treatment (24–40 kW, 4–10 min) to elucidate the evolution of microstructure, chemical composition, and micro–nano mechanical properties. Microwave irradiation induced pronounced deformation and reconstruction of parenchyma and fiber cell walls, accompanied by selective degradation of hemicellulose and rearrangement of lignin and cellulose. The relative crystallinity increased significantly from 39% to 52%, while hemicellulose content in the yellow layer decreased from 21.7% to 18.3%, accompanied by an increase in lignin content from 29.3% to 32.5%. Microwave treatment markedly enhanced nanomechanical properties: the hardness of fiber cells increased from 0.43 to 0.55 GPa to 0.65–0.80 GPa, and the elastic modulus improved from 10.88 to 11.53 GPa to 16.61–18.60 GPa. Meanwhile, the creep rate decreased by 54% (from 18.5% to 8.5%), indicating significantly improved deformation resistance. Parenchyma cells exhibited similar trends, with hardness increasing by up to 59%. At the macroscopic scale, density decreased from 0.74 to 0.58 g/cm³ , while equilibrium moisture content was reduced from 18.2% to 8.5%, demonstrating improved dimensional stability and reduced hygroscopicity. In addition, the water contact angle and antifungal resistance improved, confirming enhanced durability. These results demonstrate that microwave treatment enables simultaneous regulation of bamboo’s hierarchical structure and performance, providing a rapid, green, and controllable strategy for enhancing micromechanical properties, dimensional stability, and durability.