Structural evolution of hard-elastic polyethylene cast film in temperature-strain space: An in-situ SAXS and WAXS study

Abstract

Hard-elastic polyethylene (HEPE) cast films are the key intermediate product for producing PE microporous membranes (dry process) used as separators in Lithium battery. The effects of temperature on the deformation mechanisms of HEPE cast films are systematically studied with in-situ synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS) techniques during stretching in a wide temperature range from 25 to 135 °C. The structural evolutions and mechanical behaviors show three distinct features, which contribute to the rough divisions of the temperature space into three regions (I/II/III) with α-I relaxation temperature (TαI) and the onset melting temperature (Tonset) as the boundaries. On the basis of the evolutions of the structural parameters like long period (Lm), micro-strain (εm), orientation parameter (f200), crystallinity (Xc), and etc., lamellar separation is the main deformation mode in the linear elastic strain zone. And microphase separation of interlamellar amorphous, lamellar crystal slipping and melt-recrystallization are proposed to determinate the later non-linear mechanical behaviors in the three temperature regions, respectively. The full view of deformation mechanisms in the 2D temperature-strain space aids to deepen the understanding of the nonequilibrium structural evolutions in hard-elastic polyethylene films and guide the manufacture of high-performance microporous membranes with dry process.