A scattering study of nucleation phenomena in polymer crystallisation

The mechanism of primary nucleation in polymer crystallisation has been investigated experimentally and theoretically. Two types of experiments have been performed on polypropylene, polyethylene, and poly(ethylene terpthalate). Crystallisations with long induction times, studied by small and wide angle X-ray scattering (SAXS and WAXS), reveal the onset of large scale ordering prior to crystal growth. Rapid crystallisations studied by melt extrusion indicate the development of well resolved oriented SAXS patterns associated with large scale order before the development of crystalline peaks in the WAXS region. The results suggest pre-nucleation density fluctuations play an integral role in polymer crystallisation. A theoretical model has been developed which qualitatively describes the experimental results.