Heat of fusion of polymer crystals: Thermodynamics of melting

Abstract

Abstract The weight fraction crystallinity (Wc) of a polymer sample can be determined from the relation Wc = △Hf/△Hf°. However to obtain a more accurate determination of Wc the term △Hf should be corrected for various excess enthalpy terms. These corrections should include terms related to the nature of the “fold surface,” i. e., the manner in which units in the fold structure are distributed between true folds and cilia. They should also take into account the nature of the crystal, e.g., the possibility of an enthalpy term associated with mosaic block side surfaces in dried-down crystals. The magnitude of the appropriate correction factors (and their affect on Wc) has been estimated for various fold/cilia models. From the derived equations it is apparent that the y-intercept of a plot of the form △Hf/Wc versus (crystal core thickness)-1 is equal to △Hf° only when dealing with crystals kept in suspension. For dried single crystals the y-intercept is shown to be some function of △Hf° . Since the vast major...