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The hydrogen bonding network analysis of softwood lignin is relevant to designing novel technologies to overcome the recalcitrance of plant biomass in the industrial deconstruction and manufacturing of ligninbased carbon fibers. In this work, we examine, by atomistic simulations, the hydrogen bonding network in guaiacyl-rich lignin and guaiacyl-type lignin over a wide range of temperatures. We determine the formation of stable water-bridged dimeric complexes by the interaction of phenolic and aliphatic hydroxyl groups and π−π stacking between phenol rings, causing a slow dynamic of lignin with temperature. The interaction strength between water oxygen and hydrogen of hydroxyl groups in these lignin complexes is established. The formation of the ice crystal structure at low temperatures in the complexes explains the anti-plasticizing action of water, increasing the Young's modulus (E) of lignin systems at high hydration. Glass-transition temperature and E were successfully predicted by CHARMM force field for lignin at different hydrations.

For the engineering and process design of chemical and pharmaceutical plants, the knowledge of thermophysical properties is essential. Here, glass transition temperature (Tg), curves of heat capacity (Cp), isotropic thermal expansion (∝p), and isothermal compressibility (βT) 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 Cp, ∝p, and βT, whereas Tg is computed by monitoring specific volume versus temperature. Here, the fluctuation method is used with a quantum mechanical correction term for the calculation of Cp. Results of Cp, ∝p, and βT 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 ∝p, βT, and Tg are somewhat better reproduced than Cp 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.

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