(212b) Modeling of Swelling and Dissolution of Cellulosic Fibers for Efficient Woody Biomass Utilization

Dissolution of cellulose, a nanostructured polymer abundant in nature, is a critical step for the efficient utilization of this renewable resource as a starting material for the synthesis of high value-added functional polymers and chemicals and also for biofuel production.  The recalcitrance of cellulose microfibrils, which is a function of complex network of cellulose, partial crystalline structure, and the extended noncovalent interactions among molecules, provides the major barrier to solubility of cellulose.  There are a few solvent systems effective for direct dissolution of cellulose, and they operate under rather strict conditions of composition and temperature.  Moreover, the mechanism of cellulose dissolution from solid state to homogenous solution is not well-understood.  We present here a phenomenological model for describing the swelling and dissolution of solid cellulosic fibers.  This model is based on 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, as well as the thermodynamics and kinetics of dissolution.  The model considers cellulosic fibers as non-uniform semicrystalline polymers with different properties among their cross sections due to the different supramolecular and morphological structures of cell-walls.  The model predicts the: (i) crystalline, amorphous and solvent concentrations as functions of time and position within the fiber; (ii) fraction of fiber dissolved and the degree of crystallinity of the fiber with time; (iii) diameter of fiber as well as its swelling rate; and (iv) overall dissolution time.  The effects of various model parameters on the kinetics of dissolution are analyzed, and the results are compared with experimental studies.  The insights obtained from this model should facilitate the design of efficient solvent systems and processing conditions for woody biomass dissolution.