Nanostructure Evolution of Isotropic High-Pressure Injection-Molded UHMWPE during Heating

Ultrahigh molecular weight polyethylene (UHMWPE) is injection molded under high pressure and studied by ultra-small-angle X-ray scattering (USAXS) during melting in a time-resolved synchrotron radiation experiment. Results concerning melting and recrystallization of crystalline lamellae are compared to data obtained by differential scanning calorimetry (DSC). USAXS analysis reveals a coupled process of melting and crystallization which is not accompanied by external heat flow. Nine isotropic samples differing in molecular weight and molding pressure are heated at a rate of 5 °C/min. 2D USAXS images integrate over temperature intervals between 3 and 7 °C. The materials are considered two-phase semicrystalline polymers. Scattering curves obtained by azimuthal averaging are transformed to interface distribution functions (IDF) which are perfectly fitted by a nanostructural model comprising an ensemble of thick, uncorrelated layers (50 nm thickness) and stacks of short-range correlated crystalline lamellae (2...