Effect of High-Temperature Paraffin Impregnation on the Properties of the Amorphous Cellulose Region Based on Molecular Dynamics Simulation

Abstract

A paraffin–cellulose composite model was created using Materials Studio software, establishing a cellulose chain with a polymerization degree of 20 and paraffin molecules. A theoretical foundation for the research of wood heat treatment was established by explaining the changes in macroscopic qualities, such as mechanical properties, water absorption, etc., from a microscopic point of view. The model tended to a stable state with lower energy through geometric optimization and kinetic relaxation. The dynamics simulation was run based on this condition at a total of five different temperatures: 100 °C, 150 °C, 170 °C, 190 °C, and 210 °C. The energy balance, paraffin molecular diffusion coefficients, cell parameters and densities, hydrogen bonding numbers and mechanical parameters of the paraffin–cellulose composite model were analyzed. The results demonstrated that the paraffin diffusion range increased with temperature, and the paraffin diffusion coefficient was greatest at 210 °C, which also resulted in the maximum cell volume, the lowest density, and the lowest water absorption at this temperature. On the other hand, the paraffin–cellulose hybrid model had the most hydrogen bonds and the most stable system at 100 °C. The mechanical properties of the amorphous cellulose region of wood are influenced by temperature. According to the calculation of Lamé constants, with the system’s temperature rise, Young’s modulus (E) and shear modulus (G) were maximum at 100 °C, indicating the wood’s optimal toughness and plasticity. Poisson’s ratio and K/G values were largest at 210 °C, indicating the optimal toughness and plasticity of wood. The thermal modification of wood under different conditions can not only retain its natural advantages, but also improve its own performance, expand the application range of wood, and increase the utilization rate of wood. Therefore, the appropriate temperature and other conditions can be selected according to the actual needs of the wood heat treatment, which has significant practical significance for the study of wood heat treatment.