Water-based ultrasonic pretreatment enhances moso bamboo dimensional stability and mildew resistance

Bamboo is naturally susceptible to mould and dimensional instability under humid conditions, which limits its durability in practical applications. This study aimed to determine whether water-based ultrasonic pretreatment could improve moso bamboo's (Phyllostachys edulis) dimensional stability and mildew resistance by altering microstructure and physicochemical properties. Results showed that ultrasonic pretreatment increased the mass loss rate by 0.2-0.8 %. It reduced the hot-water extractive content by 6-7 %, and decreased absolute-dry density by 0.02-0.06 g/cm³. The treatment caused pit membrane rupture and parenchyma wall thinning (the distribution range narrowed to approximately 5.5-12.5 μm at 20-60 min), and removing amorphous components enhanced cellulose crystallinity by about 8.4 % and slightly reduced microfibril angle by 1.8 % (both at 10 min). These microstructural and physicochemical changes led to improved dimensional stability with about 0.2 % reduction in radial swelling, despite slightly higher moisture uptake. More importantly, mould resistance improved significantly. Mould infection decreased by about 20 % for A. niger (to around 45 % at 30 min) and about 83 % for P. citrinum (to about 10 % at 60 min). The findings demonstrate good potential for ultrasonic pretreatment as a green, non-chemical method to enhance moso bamboo's dimensional stability and mildew resistance. Ultrasonic pretreatment could also be combined with other modification strategies to achieve superior performance in demanding service environments.