Structure evolution of polyethylene-plasticizer fi lm at industrially relevant conditions studied by in-situ X-ray scattering: The role of crystal stress
An interesting evolution of SAXS patterns from anisotropic ring, four-point, six-point, two point is observed by Ph.D Xiaowei Chen, and this work has been published on European Polymer Journal 101 (2018) 358–367.
Structure evolution of slightly oriented polyethylene (PE)-plasticizer film is recorded with small- and wide-angle X-ray scattering (SAXS/WAXD) during stretching at temperature from 80 oC to 100 oC. An interesting evolution of SAXS patterns from anisotropic ring, four-point, six-point, two point is observed, which is validated to be resulted from melting-recrystallization. With peak shift of WAXD pattern, triaxial local stresses exerted on lamellae at different azimuthal angles are acquired. As consequence, lamellae melting is revealed to be stress induced process, where stress exerted along chain direction of lamellae and stress perpendicular to chain direction are the criteria at azimuthal angle from 0o to 60o and that from 70o to 90o, respectively. Due to the heterogeneous stress distribution of the system, the appearance of four-point pattern stems from the sequence of lamellae melting at different azimuthal angles. Through thermodynamic analysis, the physical essence of stress induced melting of lamellae is validated to be elastic energy driven crystal to amorphous phase transition.
This work is supported by the Natural Science Foundation of China (51227801, 51325301, 51633009, 51703218), China Postdoctoral Science Foundation (No. 2017M612087) and Anhui Provincial Science and Technology Major Projects (No. 16030901044). And the authors are grateful to beam line BL19U of Shanghai Synchrotron Radiation Facility (SSRF) for the provision of synchrotron beam time.
