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

Molecular-scale modeling was used to estimate the diffusion coefficient for CO2 in crystalline and amorphous cellulose. Using the molecular mechanics force field, PCFF, molecular dynamics simulations were performed on CO2-cellulose systems at temperatures between 300 and 800 K using an NPT ensemble. The mean-square displacement for CO2 molecules at each time step was measured, and the diffusivity of CO2 in cellulose calculated. For temperatures between 300 and 800 K, the diffusivity of CO2 through crystalline cellulose was estimated to be between 3.33 × 10−9 and 3.20 × 10−6 cm2 s−1, and between 2.33 × 10−8 and 9.44 × 10−6 cm2 s−1 for amorphous cellulose. The effect of temperature on the diffusivity of CO2 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.