Gamma Radiation-Induced Unsaturated P(VDF-CTFE) Membranes with Improved Mechanical Properties

Poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) membranes were prepared by drop-casting with tetrahydrofuran (THF), and were then radiated by a low dose of gamma radiation without any other reagents. The apparent colour of the freshly prepared film was a semi-transparent white, which gradually darkened and finally turned black after 10.2 kGy gamma radiation. Meanwhile, the yield and breaking strength of the membrane both improved. X-Ray diffraction (XRD) spectra showed that the structure of the microcrystal of the irradiated P(VDF-CTFE)-THF membrane was not changed. FT-IR analysis showed that the structure of the newly formed double bonds was dominated by –CF2–CF=CH–CF2–, which was formed by both dehydrofluorination and dehydrochlorination. This structure was further confirmed by 1H NMR spectra. The intermediates, such a radical-containing double bonds (–(CF=CH)n–C•F–) formed in this process were traced by electron paramagnetic resonance (EPR) spectroscopy. The thermal and mechanical properties were studied by gel permeation chromatography (GPC), thermogravimetric analysis (TGA), stress–strain and dynamic mechanical analysis (DMA), and all the changes of microstructure and optimization of apparent properties were not found in the corresponding membrane prepared by a solution-cast method with ethyl acetate (EtOAc). Therefore, this paper briefly analyses the probable mechanism of using low dose of gamma radiation to improve the mechanical properties of the P(VDF-CTFE) film prepared with THF.