Phosphoric acid membrane by radiation induced grafting of 4-vinylpyridine onto poly(ethylene-co-tetrafluoro ethylene) film followed by phosphorylation

Abstract

Proton conducting membrane prepared by phosphoric acid doping of poly 4-vinylpyridine (4-VP) grafted onto poly (ethylene-co-tetrafluoroethylene) ETFE film was studied. The effect of grafting conditions of 4-VP onto ETFE film, such as i) irradiation dose ii) monomer concentration iii) reaction time iv) reaction temperature and v) solvent type on degree of grafting (G%) was studied. The G% was found to be increased as the irradiation dose increased. Moreover, the increase in the i) monomer concentration ii) reaction time iii) reaction temperature was found to lead to an increase in the G% until a maximum value was reached at a concentration of 60 vol.% beyond which, it dropped. Among all employed solvents, ethanol for 4-VP was found to be the best diluents. Optimization using response surface method (RSM) by The Box-Behnken module available in the design expert software was used to optimize the grafting parameters; i) absorbed dose ii) monomer concentration, iii) grafting time v) grafting temperature varied in four levels in correlation with the degree of grafting G%. A maximum degree of grafting of 57% was experimentally achieved at optimum parameters; i) monomer concentration of 48 vol.% ii) absorbed dose of 64 kGy iii) reaction time of 4h iv) reaction medium temperature of 69°C. The value of G% was found to be 4% lower than that predicted by model i.e. 61%, which is very acceptable. The grafted film then functionalized with phosphoric acid doping in various G% .The membranes achieved proton conductivity as a function of level of acid doping and G%. Fourier transform infrared (FTIR), thermo gravimetric analysis (TGA) and x-ray diffraction (XRD) were used to investigate the properties of the obtained membranes and provide evidence for grafting and phosphorylation.