Isothermal crystallization of poly(glycolic acid-alt-6-hydroxyhexanoic acid) studied by DSC and real time synchrotron SAXS/WAXD

The thermal properties and the isothermal hot crystallization behavior of a new regular polyester constituted of glycolic acid and 6-hydroxyhexanoic acid units were studied by differential scanning calorimetry (DSC). The morphological development during isothermal crystallization was also investigated using simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques with synchrotron radiation. A crystalline-amorphous two-phase lamellar system was assumed and interpreted using correlation functions.Kinetic parameters deduced from the Avrami analysis indicated a three-dimensional spherulitic growth from heterogeneous nuclei, whereas optical micrographs revealed the formation of small spherulites with a negative birefringence and a fibrillar texture. The Lauritzen and Hoffman analysis of crystallization regimes was performed taking into account the kinetic constants of the overall crystallization process deduced from DSC and also the reciprocal crystallization halftimes evaluated by means of DSC, SAXS and WAXD experiments. Data were consistent with a single crystallization regime and yielded similar values for the transport activation energy and the nucleation constant in all cases.The evolution of long period and lamellar thickness was evaluated during crystallization. Changes with both crystallization time and crystallization temperature were significant.