Effect of hygrothermal-drying integrated treatment on the properties of round bamboo

The industrial utilization of bamboo is limited by drying defects such as cracking and strength loss. These issues are particularly pronounced in round bamboo (RB) due to its hollow cylindrical structure and the gradient distribution of vascular bundles and parenchyma. This study investigated an integrated hygrothermal-drying process for RB, applying saturated steam at 0.8 MPa for 4–16 h followed by low- or high-temperature drying. Dimensional variation, cracking, mechanical properties, chemical composition, and microstructure were evaluated. Results showed that steam duration and drying regime exerted distinct effects on RB behavior. Moderate hygrothermal treatment (4–8 h) with low-temperature drying effectively reduced cracking, stabilized dimensions, and maintained high bending strength and stiffness. Prolonged treatment (12–16 h) further suppressed dimensional change but caused cell wall collapse and chemical weakening, leading to strength reduction. High-temperature drying aggravated radial expansion and microstructural damage, resulting in extensive cracking and poor mechanical performance. SEM and FTIR confirmed that moderate treatment preserved cell wall integrity and chemical stability, while excessive or high-temperature conditions caused degradation. Therefore, short-term hygrothermal treatment combined with low-temperature drying provides an optimal balance between dimensional stability, structural integrity, and processing efficiency for the high-value of RB.