Effect of microwave-assisted softening on the physicochemical properties of Moso bamboo

Abstract

Bamboo possesses inherent plasticity due to its unique fiber structure, especially when subjected to softening treatments that involve moisture and heat. Softening enables bamboo to bend and deform, showcasing its excellent processing adaptability and expanding its range of applications. This study investigates the effects of microwave treatment (at 500W for 30 s with 30% moisture content), boiled-assisted microwace (100 ℃ for 2 h), and alkali-assisted microwave (0.1% NaOH for 2 h) treatments on the mechanical properties, dynamic viscoelasticity, microstructure, chemical composition, and surface wettability of bamboo at four different ages (0.6, 1, 4, and 8 years old). Microwave-assisted softening makes it easier to compress and bend bamboo strips by reducing MOR and MOE. After softening, bamboo exhibits a minimum MOR and MOE of 76.7 MPa and 458.9 MPa, respectively, and a maximum compression of 44.8%. Lignin degradation leads to the formation of new hydrogen bonds, and increased crystallinity is a common factor contributing to enhanced softening properties. The lignin structure undergoes age-related changes, which influence the dynamic viscoelasticity of bamboo. Notably, four-year-old bamboo exhibited increased thermoplasticity when the glass transition temperature decreased by 96.8, 103.5, and 104 °C under various assisted microwave softening conditions. The alkali-assisted method's degradation of hemicellulose and lignin in the Moso bamboo's cell wall was more pronounced compared to boil-assisted methods. This resulted in a loose cell wall structure that is conducive to water infiltration inside the bamboo. However, the alkali-assisted degradation negatively impacted the microstructure, surface wettability, and mechanical properties of bamboo.