Crystal size shrinking in radiation-induced crosslinking of polytetrafluoroethylene: Synchrotron small angle X-ray scattering and scanning electron microscopy analysis

The crystal structure of crosslinked polytetrafluoroethylene (XPTFE) and its morphological variations as compared with pure PTFE were investigated using differential scanning calorimetry, synchrotron small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The XFTFE samples were obtained by irradiating PTFE at the melt state using different radiation doses. Results showed that the melting temperature of the XPTFE decreases with the increase in radiation dose. The crystal melting enthalpy increases under low-dose irradiation. The scattering intensity decreases with the increase in radiation dose, which indicates the decrease in crystal size. Based on the SAXS patterns, the XPTFE crystallite size is smaller than the PTFE crystallite size. The difference in crystal sizes is more pronounced for XPTFE obtained under high radiation doses. This finding is confirmed by the SEM images of the XPTFE fractured surfaces. These results provide a reasonable explanation for the improved transparency and the relatively low crystallinity and high wear resistance of XPTFE compared with PTFE. (C) 2014 Elsevier Ltd. All rights reserved.