(276c) Swelling and Dissolution of Cellulosic Fibers: Effect of Crystallinity and Fiber Diameter

Efficient utilization of biomass is hindered by the recalcitrance to dissolution of semicrystalline cellulose. Pretreatment is often used to alter the structure of cellulosic biomass in order to make cellulose more accessible to solvents and enzymes. The pretreatment involves physical and/or chemical processing which affects the degree of crystallinity and size of biomass particles. We examine here the effects of parameters such as fiber diameter, cellulose degree of crystallinity, solvent properties, and temperature on the kinetics of swelling and dissolution. To this end we have employed a phenomenological model that is informed by experimental observations and polymer fundamentals, and incorporates the transport phenomena governing the dissolution of solid cellulose, e.g., solvent penetration, transformation from crystalline to amorphous domains, specimen swelling, and polymer chain untangling, together with thermodynamics and kinetics of dissolution. The model predicts the: (i) crystalline and amorphous cellulose and solvent concentrations as functions of time and position within the fiber; (ii) fraction of fiber dissolved and degree of crystallinity over time; (iii) fiber diameter and swelling rate over time; and (iv) total descrystallization time and total dissolution time. The insights obtained from this analysis would facilitate the rational design of pretreatment processes to reduce the size and degree of crystallinity of cellulosic biomass particles, leading to enhanced biomass utilization.