Thermophysical Properties of Amorphous-Paracrystalline Celluloses by Molecular Dynamics

For the engineering and process design of chemical and pharmaceutical plants, the knowledge of thermophysical properties is essential. Here, glass transition temperature (T-g), curves of heat capacity (C-p), isotropic thermal expansion (proportional to(p)), and isothermal compressibility (beta(T)) are computed for amorphous/paracrystalline (Am-Par) structures of cellulose over a wide range of temperature (380-680 K) using molecular dynamics with the CHARMM36 (C36) force field (FF). The fluctuation method under the NPT ensemble is used to calculate C-p, proportional to(p), and beta(T,) whereas T-g is computed by monitoring specific volume versus temperature. Here, the fluctuation method is used with a quantum mechanical correction term for the calculation of C-p. Results of C-p, proportional to(p), and beta(T) values at 298 K using extrapolation from these curves are also obtained. The thermophysical properties values from the simulations are compared with experimental data for cellulose with different degree of crystallinity and with those obtained by prominent FFs suggested for cellulose, such as GLYCAM06 and COMPASS. The findings reveal that proportional to(p), beta(T), and T-g are somewhat better reproduced than C-p with C36 over the studied temperature range. From this study, it is inferred that, for accurate modeling of heat capacity of pure Am-Par celluloses with large fragments of glucose, the C36 FF needs re-parameterization.