Molecular Dynamics Study on Mechanical Properties of Cellulose with Air/Nitrogen Diffusion Behavior

Abstract

Two hybrid models of cellulose and heat transfer media were designed to simulate changes of cellulose and gas during the heat treatment of wood. The chosen heat transfer media were air and nitrogen, and the range of selected simulation temperature was from 450 to 510 K. The diffusion coefficients of air and nitrogen both increased as the temperature increased, and the diffusion coefficient and amplification of air were larger than that of nitrogen. In addition, the calculation of free volume (fraction) confirmed this conclusion. The mechanical parameters of cellulose were analyzed in terms of the Young's modulus, Poisson's ratio, and the ratio of bulk modulus to shear modulus (K/G), which were affected by the temperature and heat transfer medium. Compared with the nitrogen model, the cellulose in the air model decreased in the Young's modulus and K/G as the temperature increased, while the Poisson's ratio increased. Young's modulus and K/G were larger when the heat transfer medium was nitrogen, and the Poisson's ratio was superior to nitrogen in the air environment. The rate of change of mechanical parameters of cellulose in the air system was greater than that of nitrogen, which was related to the larger diffusion coefficient of air.