Perfluorinated Ion Exchange Membranes

The requirements for ion-exchange membranes in membrane cell caustic-chlorine process are : high permselectivity, low electric resistance, excellent chemical resistance to oxidants and alkali, good heat resistance, low diffusion of salt and low permeability to water and good mechanical properties. Chemical resistance to oxidants in particular could not be achieved in conventional hydrocarbon type ion-exchange membranes, although various electrolytic methods were tried to prevent ion-exchange membranes of that type from deteriorating by oxidants. In 1972, the difficulty in chemical resistivity was overcome by perfluorocarbon ion-exchange membrane made by du Pont de Nemours and Co. (1). but this membrane was still too low in permselectivity while its electric resistance was sufficiently low. The low electric resistance and high permselectivity are factors generally forced to be mutually inconsistent. However, the use of an anisotropic structure for ion-exchange membranes enables both of these requirements to be achieved together (2,3). Anisotropic ion-exchange membranes like