Cellulose Aggregation under Hydrothermal Pretreatment
Conditions
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Abstract
Cellulose, the most abundant biopolymer
on Earth, represents a
resource for sustainable production of biofuels. Thermochemical treatments
make lignocellulosic biomaterials more amenable to depolymerization
by exposing cellulose microfibrils to enzymatic or chemical attacks.
In such treatments, the solvent plays fundamental roles in biomass
modification, but the molecular events underlying these changes are
still poorly understood. Here, the 3D-RISM-KH molecular theory of
solvation has been employed to analyze the role of water in cellulose
aggregation under different thermodynamic conditions. The results
show that, under ambient conditions, highly structured hydration shells
around cellulose create repulsive forces that protect cellulose microfibrils
from aggregating. Under hydrothermal pretreatment conditions, however,
the hydration shells lose structure, and cellulose aggregation is
favored. These effects are largely due to a decrease in cellulose–water
interactions relative to those at ambient conditions, so that cellulose–cellulose
attractive interactions become prevalent. Our results provide an explanation
to the observed increase in the lateral size of cellulose crystallites
when biomass is subject to pretreatments and deepen the current understanding
of the mechanisms of biomass modification