Thermal and microstructural behavior of poly(ethylene-co-tetrafluoroethylene) films upon gamma and electron beam irradiation

The thermal and microstructural features of poly(ethylene-co-tetrafluoroethylene) (ETFE) films exposed to gamma and electron beam (EB) radiation upon a dose range of 0–400 kGy are investigated systematically by thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), Raman spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). Raman spectra show the dominant bond breaking of the side chains as compared with the main chains (C–C). Activation energy for decomposition temperature provides an indication of recrystallization of the newly shorter segments in the initial dose range of 0–50 kGy (from 103 to 134 and 152 kJ/mol for gamma and EB irradiation, respectively) and degradation in the inherent and newly generated crystallite regions in the higher doses of 50–400 kGy (134 → 89 and 152 → 89 kJ/mol for gamma and EB irradiation, respectively). The inherent crystallite region was modified dramatically as qualitatively determined by the decrease in the crystalline lamellar thickness from 5.8 to 4.7 and 4.2 nm for gamma and EB irradiation, respectively. Note that the new crystallites are found to be generated on the inherent crystallite surfaces and within the lamellar boundaries rather than within the amorphous phase. The surface features of ordered polymer chains become elongated, diffused, and distorted at higher levels with increase of irradiation doses. The electron irradiation induced more pronounced alternations in structural features and thermal properties than the gamma irradiation. • Recrystallization of newly shorter segments and degradation in the inherent crystallite region are observed. • The crystalline lamellar thickness determined for the first time decreases with irradiation dose. • New crystallites are generated mostly on the inherent crystallite surfaces. • Electron irradiation induced more pronounced alternations than gamma one.