With the guidance of Prof. Li and associate Prof. Chen, the synergistic and competitive effects of temperature and flow on crystallization of polyethylene during film blowing were studied by Master Haoyuan Zhao et al. The related work has been published in ACS Applied Polymer Materials.
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 Xray 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.
This work is supported by the National Key R&D Program of China (2016YFB0302500) and the National Natural Science Foundation of China (51703217 and 51633009). The experiments are carried out in Shanghai Synchrotron Radiation Facility (SSRF).
Related links:https://pubs.acs.org/doi/10.1021/acsapm.9b00391
