The modeling of cellulose is examined. The temperature-dependent structure and dynamics of individual softwood lignin polymers in aqueous solution have been examined using extensive molecular dynamics simulations. With decreasing temperature the lignins are found to transition from mobile, extended to glassy, compact states. The low-temperature collapse is thermodynamically driven by the increase of the translational entropy and density fluctuations of water molecules removed from the hydration shell, thus distinguishing lignin collapse from enthalpically-driven coil-globule polymer transitions and providing a thermodynamic role of hydration water density fluctuations in driving hydrophobic polymer collapse. Lignin also forms aggregates in vivo and poses a barrier to cellulosic ethanol production. Neutron scattering experiments and molecular dynamics simulations reveal that lignin aggregates are characterized by a surface fractal dimension that is invariant under change of scale from 1�1000A. The simulations also reveal extensive water penetration of the aggregates and heterogeneous chain dynamics corresponding to a rigid core with a fluid surface. The interaction of lignin with cellulose is examined and differential binding to crystalline and amorphous cellulose explained thermodynamically. A combination of small-angle scattering and simulation explains stem-explosion biomass changes.

Computer simulation of pretreatment of lignocellulosic biomass in cellulosic ethanol production

245th National Meeting (2013)

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