Microwave-Assisted Heat Treatment for Sustainable Wood Modification: Enhanced Dimensional Stability and Selective Control of Volatile Organic Compound Emissions

Conventional air heat treatment (Air-HT) suffers from low energy efficiency and excessive volatile organic compound (VOC) emissions, limiting its sustainable implementation. This study evaluates microwave-assisted heat treatment (Mic-HT) of Afrormosia wood at 160, 180, and 200 °C as a sustainable alternative. The results showed that Mic-HT can reduce energy consumption by 10.26%–15.16% relative to Air-HT. At 180 °C, this process significantly enhanced mass loss (75.37% increase) and reduced equilibrium moisture content (4.06% decrease) compared to Air-HT. The treatment improved dimensional stability by 20%–42%, resulting in equivalent dimensional stabilization at lower temperatures (M180 ≈ A200). Mic-HT induces anisotropic color changes in transverse darkening at lower temperatures and intensified chromatic alterations at higher temperatures (L*, a*, and b* values at 200 °C exceeding Air-HT by 7.71%, 21.94%, and 26.17%, respectively). VOC profiling revealed a fundamental transition from aldehyde-dominated to phenol-dominated emissions (>40% total VOCs), suppressing straight-chain aldehydes (>99%) and reducing VOC complexity by 60% at 180 °C. Under the combined action of thermal, nonthermal, and selective effects, Mic-HT enables energy-efficient wood modification with enhanced dimensional stability, anisotropic coloration, and selective emission control. This approach supports sustainable, emission-controllable wood processing aligned with carbon neutrality objectives.