Effect of electron beam irradiation on structural and thermal properties of gamma poly (vinylidene fluoride) (γ-PVDF) films

In this study, we successfully prepared the pure PVDF film containing almost exclusive gamma-phase (gamma-PVDF) using 15 wt% solution in N, N-dimethylformamide. These gamma-PVDF films were irradiated by 3.0 MeV electron beam in vacuum at room temperature up to 358 kGy. The effect of the irradiation on the chemical structural and thermal properties of pristine and irradiated gamma-PVDF films were detailedly investigated by FTIR, XRD and DSC, respectively. DSC results show that two single and different melting endotherms from the successive heating curves correspond to gamma-phase and alpha-phase, respectively. FTIR results show that the characteristic absorption peaks corresponding to gamma-phase do not shift, and the C-C bond formation is not significantly observed in the irradiated gamma-PVDF films until above 30 kGy. XRD results show that the crystal form of gamma-PVDF is not influenced significantly by irradiation. All PVDF films exhibit a single melting endotherm, irrespective of the irradiation dose. Two superpositioned crystallization peaks were observed for PVDF films only irradiated at high dose of 232 and 358 kGy, which can be related to the fractionated crystallization of irradiated PVDF. The dependences of thermal characteristics on the irradiation dose were detailedly investigated by DSC in this study.