The effects of EB-irradiation doses on the properties of crosslinked SPEEK membranes

In this study, sulfonated poly(ether ether ketone) (SPEEK) membranes with a crosslinked structure were prepared by the EB-irradiation crosslinking of a mixture of SPEEK and crosslinkers with various irradiation doses. The crosslinked membranes were utilized as proton exchange membranes (PEM) for fuel cell application. The pure SPEEK and crosslinked SPEEK (CSPEEK) membranes were characterized by using H-1 and C-13 NMR spectroscopy, gel fraction, and a dynamic mechanical analysis (DMA). It was observed that the sulfonic acid groups were introduced exclusively to the hydroquinone segments after the treatment of PEEK with concentrated sulfonic acid and the degree of sulfonation was measured to be 0.69 from the NMR peak integration. The gel fraction study of EB-treated SPEEK membranes indicates that the EB-irradiation doses have a direct effect on the degree of crosslinking. The DMA and SAXS results showed that the CSPEEK membranes have well-developed ionic aggregation in the cluster region. These results indicate that the ionic aggregations of the SPEEK membranes are not largely affected by irradiation. The water uptake of the CSPEEK membranes was found to be lower than 30% at room temperature, and the proton conductivity to be higher than 10(-2) S/cm. Finally, the current densities of the CSPEEK membranes irradiated with 50, 100, and 200 kGy, were measured to be 221, 482, and 522 mW/cm(2), respectively, at a violated of 0.4 V and at 80 degrees C. The overall findings suggest that the CSPEEK membranes prepared by EB irradiation are expected to be useful for PEMFC since they exhibit high dimensional stability as well as good cell performance. (C) 2012 Elsevier B.V. All rights reserved.This research was supported by Nuclear R&D program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology Korea. The small-angle X-ray scattering experiments at PLS were supported in part by the Ministry of Education, Science and Technology Korea and Pohang Steel co. The authors thank Korea Basic Science Institute (KBSI) Jeonju Center for help with the FE-TEM measurements