Structural and property changes during uniaxial drawing of ethylene-tetrafluoroethylene copolymer films as analyzed by in-situ X-ray measurements

Abstract The structure–property relationship during uniaxial drawing of high-molecular-weight ethylene–tetrafluoroethylene copolymer (ETFE) film was analyzed based on a combination of in - situ wide-angle X-ray diffraction (WAXD) and stress measurements. In - situ WAXD patterns indicated that the hexagonal (100) reflection transformed from the initial un-oriented ring into equatorial spots via split arcs at temperatures both below and above T g , but that the critical strain when such transition occurred was delayed above T g . Drawing above T g produced an equatorial concentration of the spot reflections; thus, the extended chain crystal was enhanced as a result of elongation of the strain-hardening region. In contrast, the draw below T g remained less oriented even just before breaking. However, the high orientation component also appeared beyond the critical strain; it could be assigned to the so-called “tie molecules” that bind the deformed lamellae. Changes in resultant tensile strength could be interpreted by these extended chain crystals and characteristic tie molecule components.