UV radiation induced graft copolymerization of allyl acetate onto poly(ethylene terephthalate) (PET) films for fuel cell membranes

Ultraviolet (UV)-induced graft copolymerization of allyl acetate (AA) monomer onto poly(ethylene terephthalate) (PET) films and the subsequent sulfonation on the monomer units in the grafting chain using chlorosulfonic acid (ClSO₃H) were carried out to prepare proton exchange membranes (PEMs) for fuel cells. A maximum grafting value of 12.8% was found for 35 vol% allyl acetate after 3 h radiation time. Optimum concentration of ClSO₃H was selected for the sulfonation reaction to be 0.05 mol/L based on the degree of sulfonation and the tensile strength studies of the membrane. The degree of sulfonation increased as the sulfonation reaction temperature and sulfonation time were increasing. The radiation grafting and the sulfonation have been confirmed by titrimetric and gravimetric analyses as well as FTIR spectroscopy. The maximum ion exchange capacity (IEC) of 0.04125 mmol g⁻¹ was found at 12.1% degree of sulfonation and the maximum proton conductivity was found to be 0.035 S cm⁻¹ at 30°C and a relative humidity of 60%. The various physical and chemical properties of the PEMs such as water uptake, mechanical strength, thermal durability and oxidative stability were also studied. To investigate the suitability of the prepared membrane for fuel cell applications, its properties were compared with those of Nafion 117.