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

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 Tg, but that the critical strain when such transition occurred was delayed above Tg. Drawing above Tg 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 Tg 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.