Diffusion of CO2 and fractional free volume in crystalline and amorphous cellulose

Abstract Molecular-scale modeling was used to estimate the diffusion coefficient for CO 2 in crystalline and amorphous cellulose. Using the molecular mechanics force field, PCFF, molecular dynamics simulations were performed on CO 2 -cellulose systems at temperatures between 300 and 800 K using an NPT ensemble. The mean-square displacement for CO 2 molecules at each time step was measured, and the diffusivity of CO 2 in cellulose calculated. For temperatures between 300 and 800 K, the diffusivity of CO 2 through crystalline cellulose was estimated to be between 3.33 × 10 −9 and 3.20 × 10 −6  cm 2  s −1 , and between 2.33 × 10 −8 and 9.44 × 10 −6  cm 2  s −1 for amorphous cellulose. The effect of temperature on the diffusivity of CO 2 is small with an activation energy of between 16.5 and 16.9 kJ/mol for crystalline cellulose and between 10.2 and 15.1 for amorphous cellulose.