Molecular dynamics modeling and experimental validation of wood lignin tensile behavior under varying moisture...

Mechanical characterization of wood lignin is crucial for elucidating the intrinsic mechanical behavior of wood. However, the tensile properties of in situ lignin remain underexplored. This study investigates the effects of molecular structure and environmental factors (moisture and temperature) on the tensile behavior of in situ hardwood (birch) and softwood (Chinese fir) lignins via molecular dynamics (MD) simulations. The tensile properties obtained from the MD simulations are partially validated against experimental data obtained from alkaline-treated triple-enzyme lignin (ATEL). The MD simulations reveal a pronounced moisture-dependent reduction in tensile strength and Young's modulus for both in situ birch and in situ Chinese fir lignins. The mechanical performance of these lignins peaks near 20 °C and decreases at higher temperatures. At 20 °C and 3.5% moisture content, in situ birch lignin exhibits a tensile strength of 196 MPa and a Young's modulus of 3.4 GPa. In contrast, in situ Chinese fir lignin exhibits a tensile strength of 198 MPa and a Young's modulus of 3.52 GPa. Experimental tensile testing further confirms the strong moisture sensitivity of lignin. As the moisture content increases from 3.5% to 12.7%, the Young's modulus of birch ATEL decreases from 5.8 GPa to 1.4 GPa. Although MD-predicted values differ quantitatively from the experimental measurements, the overall trends remain consistent. This study establishes structure-property relationships between the in situ molecular structure of lignin and its environmental responsiveness. These findings provide valuable molecular-level insights for designing and optimizing adaptive lignin-based biomaterials under variable service conditions.