(571f) Solvent-Induced Decrystallization of Cellulose: Thermodynamics, Transport, and Kinetics

A major barrier to the efficient utilization of biomass is the recalcitrance to dissolution of cellulose, presenting crystallinity and extensive noncovalent interactions (e.g., hydrogen bonding and hydrophobic).  Despite extensive research, the cellulose intra- and inter-molecular interactions and dissolution mechanism remain elusive.  In general, the dissolution of semi-crystalline polymers such as cellulose comprises several steps including solvent penetration, amorphous polymer swelling, chain untangling, and decrystallization of crystalline domains.  The solvent-induced transformation of crystalline to amorphous domains is a rate-controlling step in the dissolution of cellulose.  We have obtained an expression for the decrystallization rate constant, considering the free energy changes during this process.  The proposed decrystallization rate constant is a function of the supramolecular and morphological structure of cellulose, physico-chemical properties of solvent, and temperature.  This rate constant is invoked for modeling the decrystallization of cellulosic fibers in different solvent systems.  The obtained modeling predictions are compared with experimental results.  The effects of various parameters, such as cellulose degree of polymerization, crystal size, and temperature, on the kinetics of the process are discussed.  The insights obtained from this analysis facilitate the design of efficient solvent systems and conditions for biomass processing.