Melting Behavior of lrradiated Poly(vinylidene fluoride)

Abstract

The melting and crystallization behavior of poly(vinylidene fluoride) (PVdF) before and after irradiation has been observed by the use of a differential scanning calorimeter (DSC). Gamma irradiation was carried out with 6 Co at a dose rate of 1 MR/hr at ambient temperature. Electron beam irradiation was carried out with EBG at 2 MeV and at a dose rate of 2MR/pass by intermittent irradiation to prevent a rise in temperature by means of a shuttle conveyor.
Melting temperature (T.) and crystallization temperature(T.) were measured at the peak in the DSC thermograms. T. decreased with increaseing radiation dose. PVdF, irradiated in vacuum, gave mostly a simple and sharp peak.
On irradiation in air, more complex peaks were observed. These results indicate that the melting behavior is strongly affected by the presence of oxygeR during the irradiation. Depressions of T. and T, were the same fer gamma and electron irradiation in vacuum. On the other hand, T. depression of PVdF by the irradiation in air was smaller than that in vacuum, and a difference in melting peint depression between gamma and electron irradiation was also observed.
The peak at higher temperature corresponds to crystalline state where the degradation dqe, to irradiation is mainly preduced by the presence of suMcient oxygen near the film surface. While, the peak at lower temperature corresponds to crystalline phase where crosslinking mainly takes place by irradiation in the absence of oxygen at inner parts of the film similar to the vacuum irradiation, When crosslinks are introduced, defects would be produced in the crystalline lattice. The defects would cause a melting point lowering, the magnitude of which is larger than that produced by the scission of molecular chain in the crystalline phase on irradiation in air.
Both heat of fusion and crystallinity decreased with increasing radiation dose. About 1706. decrease of heat of fusion was observed after 200 MR irradiation. On the other hand, X-ray diffraction pro es did not change markedly. The decrease in the crystallinity, determined from X-ray diffraction, was 7fZe.