Synergistic and Competitive Effects of Temperature and Flow on Crystallization of Polyethylene during Film Blowing

The influences of both temperature and external flow field on film blowing have been studied with a combination of a custom-built film blowing device and in situ synchrotron radiation small-and wide-angle X-ray scattering techniques. Polyethylene (PE) with different structural topologies, namely linear (MPE) and long-chain branched polyethylene (LPE), was used here with different responses to temperature and flow. The MPE film shows a spherulite-like superstructure with low orientation independent of take-up ratio (TUR), while the LPE has a typical row-nucleated structure at high TUR. But for LPE film obtained at low TUR, it exhibits the combination of both crystal morphologies. Further analysis of the microscopic structural evolution of PE during film blowing by synchrotron X-ray scattering reveals three different types of network evolution: (i) the temperature-induced crystallization (TIC) dominated process (MPE); (ii) the flow-induced crystallization (FIC) dominated process (LPE with high TUR); and (iii) nucleation and growth determined by the coupling effects of both temperature and flow (LPE with low TUR). The current results are expected to guide the processing of film blowing as well as provide a new viewpoint for FIC study under far-from-equilibrium conditions.