Improvements in ion exchange membranes

Ion-exchange membranes are made by milling together (while heated to a thermoplastic condition and in an inert atmosphere) polystyrene, or a thermoplastic copolymer of styrene, and a water-insoluble thermoplastic aliphatic polymer such as polyethylene, until a homogenous thermoplastic dispersion has been obtained, converting this dispersion into a sheet or film and thereafter subjecting the sheet or film to a chemical treatment so as to introduce ion exchange groups into the styrene units while leaving the aliphatic units of the polymeric sheet or film substantially unaffected. The exchange groups introduced may be sulphonic or amino-groups. The sulphonic groups may be introduced, for example, by treating the sheet of film with chlorosulphonic acid. The copolymer of styrene may consist of 15 parts of butadiene and 85 parts of styrene. The milling may be carried out in an enclosed apparatus, from which the air is excluded and replaced by an atmosphere of nitrogen.