Mitigating structural recalcitrance: Microwave pretreatment governs anatomy-dependent moisture migration and...

Microwave pretreatment is a promising strategy for improving the processability of lignocellulosic bioresources, yet its effectiveness in bamboo is strongly constrained by anatomical heterogeneity, particularly the recalcitrant node structure. Here, moso bamboo specimens with and without nodes were pretreated at 3, 6, and 9 kW prior to convective drying to elucidate how microwave energy regulates moisture migration and dimensional stability in an anatomy-dependent manner. Temperature profiling, layered moisture analysis, drying kinetics, shrinkage behavior, equilibrium moisture content, and microstructural observations were combined to reveal the underlying mechanism. Microwave pretreatment redistributed internal moisture and promoted vapor-pressure-driven radial moisture transfer during the early stage of drying, although the total drying duration was not markedly shortened. In internodal bamboo, this effect facilitated apparent radial moisture transport and alleviated drying stress, leading to a 39% reduction in radial shrinkage at 9 kW. By contrast, node-containing specimens exhibited a more heterogeneous thermal and drying response under the same high-power treatment. At 9 kW, pretreatment increased the initial maximum drying rate of node-containing specimens, but also induced localized structural damage, as indicated by crack formation and tissue deformation, resulting in a 36% increase in tangential shrinkage. These results highlight the need for anatomy-aware microwave pretreatment to mitigate structural recalcitrance and improve the efficient valorization of bamboo as a lignocellulosic bioresource.