Modifications of Gamma poly (vinylidene fluoride) (γ-PVDF) films by high-energy electron beam irradiation

It is a challenge to intentionally prepare the pure PVDF film containing exclusive γ-phase (γ-PVDF film). In this study, the γ-PVDF film containing extremely rare β-phase was prepared by solution casting method. γ-PVDF films were then irradiated with 2.5 MeV electron beam in vacuum at 92, 442 and 993 kGy, respectively. Modifications of γ-PVDF films by the irradiation were detailedly investigated by FTIR, DSC, TGA and XPS measurements. FTIR results show that the irradiation does not induce the crystal phase transition and carbon-carbon double bonds (C=C bonds) are obviously formed for γ-PVDF films when irradiated at high dose of 442 and 993 kGy. In addition, the evolution process of chemical structures was proposed for γ-PVDF films by the irradiation at different dose based on FTIR and XPS analyses. For thermal properties, the irradiation decreases the melting and crystallization temperatures, and thermal decomposition temperature for γ-PVDF film due to the irradiation-induced damage effects. The sample irradiated at 92 kGy has the maximum melting and crystallization enthalpies. However, the irradiation increases the residual yield at high temperature (> 500 °C) of γ-PVDF film due to the formation of crosslinked network structures in the irradiated samples.