FREE RADICALS STABILITY INVESTIGATION BY ELETRON PARAMAGNETIC RESONANCE (EPR) OF ELETRON-BEAM IRRADIATED FLUOROPOLYMER FOR FUEL CELL PRODUCTION

摘要

The alkaline anion exchange membranes (AAEM) have been produced from the irradiation method to graft functional monomers into polymer films via copolymerization by using either simultaneous or pre-irradiation methods, by means of gamma rays or electron-beam. The pre-irradiation method has been widely used due to a reduced formation of homopolymers. The graft also may be carried out at any moment after free radicals formation. Lifetime of the active species formed during polymer irradiation (radicals, ions and peroxides) is very important and may be controlled either by temperature reduction or vacuum use. In high temperatures, active species undergo decay as a result of recombination in the amorphous phase. The loss of radicals during storage affects the graft reaction, such as reduction of active centers, graft yield and membrane properties. Storage of pre-irradiated polymer is an important factor to be considered when preparing membranes for alkaline fuel cells. For during two months, the free radical decay time of polymeric films storage at ambient and low temperature was studied by Electron Paramagnetic Resonance (EPR): the films radicals hold at low temperature showed good stability and grafting yield even after two months of irradiation. This preliminary result indicates that graft of monomer onto the polymeric irradiated film can be done some time later after irradiation. Further tests in membranes and under different conditions will be carried out for more consistent and reliable results.