Power/intensity-threshold effects of ultrasonic pretreatment on microstructural remodeling and dimensional stability in moso bamboo

Abstract Ultrasonic pretreatment offers a green strategy to modify bamboo structure and improve dimensional stability. However, power/intensity-threshold effects of ultrasonic pretreatment on microstructural remodeling and dimensional stability in moso bamboo ( Phyllostachys edulis ) remain unclear. In this study, moso bamboo was treated at powers ranging from 0 to 400 W (0–2.522 W cm −2 ) to evaluate changes in microstructure, chemistry, and hygroscopic properties. Results showed that above 360 W (2.2 W cm −2 ), luminal deposits and pit membranes were greatly removed; parenchyma double-wall thickness decreased by up to 15.1 %, while mass loss rose by up to 36.2 %; crystallinity increased by 18.5 %. ATR–FTIR showed attenuation of hemicellulose and lignin bands, suggesting leaching of amorphous components during ultrasonic treatment. Microfibril angle decreased at moderate intensity and partially recovered at higher levels. These microstructural and physicochemical changes resulted in improved dimensional stability, with a reduction of approximately 0.74 % in radial swelling (360 W, 2.236 W cm −2 ), despite a slightly higher moisture uptake. These results indicate that the response intensifies in the ∼360 W region, suggesting a practical threshold region for balancing structural debridement, chemical refinement, and dimensional stability in bamboo. Ultrasonic pretreatment thus holds promise for enhancing performance in bio-based composites and engineered bamboo products.