Effects of microwave softening treatment on dynamic mechanical and chemical properties of bamboo

Abstract

Bamboo is a high-quality biomass material, but its thin walls and hollowness, limit subsequent processing. Softening can flatten and bend bamboo without causing cracks, and thus enables efficient value-added use. In this study, the effects of microwave softening parameters (microwave power, processing time, and initial moisture content) on the glass transition temperature, compression ratio, microstructure, chemical composition, and surface wettability of Phyllostachys. edulis and Dendrocalamus. sinicus were studied. Microwave softening parameters (microwave power, treatment time, initial moisture content) improved the flexibility and processability of both bamboo species. Dynamic mechanical analysis showed the storage modulus of D. sinicus slices was reduced from 7846 to 4498 MPa, which was 1.06 times higher than that of P. edulis. The glass transition temperature was lowered from 221.25 to 123.67°C, which was1.07 times higher than that of P. edulis, indicating bamboo stiffness was reduced and elasticity was enhanced. Moreover,P. edulis has higher thermoplastic quality than D. sinicus. Water molecules have a wetting and swelling effect on the cell wall. With a rise in water content, the free hydroxyl group increased, and the compression ratio of P. edulis with a moisture content of 90% increased from 15.65–45.54%, and that of D. sinicus increased from 11.31–41.67%. Hence, choosing the most adaptable bamboo species and moisture content, and increasing the softening temperature and softening time can improve the flattening quality of bamboo and effectively reduce the number of hydroxyl and carbonyl groups, and thus offers a theoretical basis for the industrial processing of bamboo timbers.