In-situ synchrotron SAXS and WAXS investigations on deformation and α-β transformation of uniaxial stretched poly(vinylidene fluoride)

The crystalline structure evolution of poly(vinylidene fluoride) (PVDF) during tensile deformation at 60 degrees C, 140 degrees C and 160 degrees C, i.e. between the glass transition temperature (T-g) and the melting temperature (T-m), was investigated by in-situ synchrotron SAXS and WAXS techniques. The analysis of the obtained scattering results indicated either yielding or alpha-beta transformation in PVDF occurred and initiated at almost the same strain level with different stretching temperatures. A deformation mechanism was proposed for PVDF to illustrate the structure evolution during uniaxial stretching at high temperature indicating that the initial crystallite and crystalline lamellae structures of stretched PVDF are destroyed and orientated not simultaneously, which is intimately related to the yield point and the initial of alpha-beta transformation on a certain degree of orientation. The long period along tensile direction increases to a maximum and then drops into a lower but stable value during this stage of deformation.