Effect of gamma radiation on crosslinking, water uptake and ion exchange on polystyrene-co-acrylic acid copolymers useful for fuel cells

Abstract

Abstract Copolymers of styrene-co-acrylic acid were synthesized by radical bulk copolymerization and sulfonated during 3 different periods of time (1, 2 or 3 h). Sulfonation reactions were carried out with sulfuric acid catalyzed with silver sulfate, at a level of 170% of benzene rings theoretically present in the copolymer. Membranes of the sulfonated copolymers were prepared by casting from their THF solutions and then subjected to gamma irradiation treatment at several doses (50, 75 and 100 kGy) in an industrial irradiator. Tg by DSC, thermal stability by TGA, water retention capacity by WU and ionic properties by IEC measurements evaluated irradiation effect on sulfonated membranes. Sulfonation reduce Tg transition and thermal stability of the copolymer (already reported), but irradiation partially recover such values; particularly for the less sulfonated material (1 h) for both, Tg and stability in the region of 200–300 °C, where sulfonated groups start to decompose. Water uptake (WU) and IEC values, as expected, are higher for more sulfonated membranes; but such values are reduced along radiation dose, ending in almost half their values at 100 kGy, after their corresponding values on non-irradiated sulfonated membranes. The general view is that gamma radiation induced crosslinking to give benefits for mechanical and thermal stability, but ion exchange properties are affected when sulfonic groups are used to crosslink the copolymer matrix.