Dissolution of semicrystalline polymers: Numerical modeling and parametric analysis
Singapati, Abhiram Yadav
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Polymer chain crystallinity and organization in fibers significantly affects the dissolution of semicrystalline polymers and constrains their subsequent physical or chemical processing. We present here a phenomenological model for describing the swelling and dissolution of semicrystalline polymeric fibers. This model is based on the transport phenomena governing the dissolution of semicrystalline polymers, 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 predicts the: (i) crystalline, amorphous and solvent concentrations as functions of time and position within the fiber; (ii) fraction of polymer dissolved and the degree of crystallinity of the polymer with time; (iii) diameter of polymeric fiber as well as its swelling rate; and (iv) overall dissolution time. The insights obtained from this study should increase the understanding about the mechanism of semicrystalline polymer dissolution and guide the design of efficient solvent systems for this process. The first section of this thesis covers a brief introduction in the importance of polymer dissolution and its application as well as the polymer dissolution mechanisms and the previously proposed models for this process. The second section presents the new mathematical model for dissolution of semicrystalline polymers, including transport phenomena equations and kinetics of this process, followed by the numerical solution algorithms. The third section presents modeling results and parametric sensitivity studies on the main physical factors that affect the mechanism of swelling and dissolution of semicrystalline polymers: the decrystallization rate constant, disentanglement rate, and disentanglement threshold.