Patent GB-1038777-A (GB)
Title: Improvements relating to ion-exchange materials
IPC: C08J5/22
Filed: 1963-05-03
Abstract: For the generation of an acid or base there is arranged in order between cathode and anode an anion-exchange membrane, a cation-anion bipolar membrane and a cation-exchange membrane, acid being formed on the cathode side of the bipolar membrane and base on the anode side. A stainless steel cathode and a Pt screen anode may be employed at a current density of 10 mA/cm2. Any electrolyte may be employed, an example being N/100 KCl.  If it is desired to avoid precipitation of a metal hydroxide in the cell, the compartment on the anode side of the bipolar membrane may be fed with plain water.  It is stated that if instead this compartment contains sodium citrate, citric acid forms therein and the sodium ion is transferred to the cathode compartment.  The bipolar ion-exchange membrane comprises two layers of thermoplastic homogeneous synthetic organic polymeric material, one cationic and the other anionic, united over the whole common interface.  Examples are given of the production of laminated membranes with both layers derived from polythene-styrene graft polymer films, glass fibre-reinforced PTFE, and of a polythene-styrene graft polymer anion-exchange layer coated with a syrup in aqueous sulphuric acid of formalin and p-phenolsulphonic acid and subjected to low-temperature curing or a syrup which cures to a cross-linked acrylamide polymer forming the cation-exchange layer.  Examples are also given of a polythene-styrene graft copolymer film which has been treated with chlorosulphonic acid being treated on opposite sides with NaOH and N-methylpiperazine to form cation-and anion-exchange materials and of an anion-exchange layer being sandwiched between two cation-exchange layers.  By varying the laminating conditions, bipolar membranes of different resitivities are obtained and reference is made to a step-junction bipolar membrane having a greater resistivity in one direction across the interface than in the other.ALSO:A bi-polar ion-exchange component comprises two layers of thermoplastic homogeneous synthetic organic polymeric material united throughout their interface, the layers being of cation- and anion-exchange material respectively. The components may be in film, tubular, wafer or other form.  When pressed lightly together at comparatively low fusing temperature, the layers unite peelably and form a high resistance unit usable as a rectifier or for switching; fusing at a higher temperature and pressure results (owing to interpenetration of the material) in a lower resistance unit useful in electrochemical reactions involving changes in acidity or alkalinity.  Combinations of high resistance units may be used as radio-frequency amplifiers.  In Examples (1). Low-density polythene films are heated in monomer-grade styrene containing benzoyl peroxide to form a graft polymer and washed with ethylene dichloride; one film is then chlorosulphonated and treated with sodium hydroxide, and a second is treated with stannic chloride and paraformaldehyde in chlormethyl methylether followed by aqueous trimethyl amine and HCl; equal size pieces of the washed and dried films are superposed, sandwiched between aluminium foils, and pressed for two minutes at 160 DEG  C. and 500 p.s.i. pressure.  (2) The treatment of the films is reversed, the first being acid- and the second alkali-treated, the dried films are hot-pressed at 400 p.s.i. for 30 seconds only.  (3) Similar treatments, with higher temperatures and pressures, are applied to films of high density polythene and to polytetrafluoroethylene reinforced with glass fibres respectively. (5) A piece of anion-exchange film placed on aluminium foil has cured on it a syrup of aqueous p-phenol sulphonic acid and formalin which has been warmed until viscous.  (6) A film of chlorosulphonated polythenestyrene copolymer supported vertically between hollow glass clamps has diffused into it through the clamps sodium hydroxide solution coloured pink with phenol-phthalein and N-methyl piperazine coloured blue with pyronine B respectively; the diffusion can be observed by the dyes and when the reagents meet in the centre of the film the latter is removed and heated at 650 DEG C. for four hours to produce a bipolar anion-cation exchange component.  (7) A mixture of acrylamide, N:N1-methylene bis-acrylamide, ammonium persulphate and sodium hydrosulphide is poured on to and cured on a portion of anion-exchange chlorosulphonated polythene-styrene copolymer film to produce a high resistance bipolar membrane.  (8) Two pieces of anion-exchange film and an interposed piece of cation-exchange film are pressed at 125 DEG  C. and 400 p.s.i. for 10 seconds between aluminium foils to produce a radio frequency amplifying unit.ALSO:A bi-polar ion-exchange component comprises two layers of thermoplastic homogeneous synthetic organic polymeric material united throughout their interface, the layers being of cation- and anion-exchange material respectively.  The components may be in film, tubular, wafer or other form.  When pressed lightly together at comparatively low fusing temperature the layers unite peelably and form a high resistance unit usable as a rectifier or for switching; fusing at a higher temperature and pressure results, (owing to interpenetration of the material) in a lower resistance unit useful in electrochemical reactions involving changes in acidity or alkalinity.  Combinations of high resistance units may be used as radio frequency amplifiers. In modifications (a) one layer may be prepared by polymerization on the other, and the second layer may be thermosetting instead of thermoplastic, (b) the unit may be made by diffusion of anion- and cation-exchange material respectively into opposite sides of a single polymeric membrane.  In Example (1). Low-density polythene films are heated in monomer-grade styrene p  containing benzoyl peroxide to form a graft polymer and washed with ethylene dichloride; one film is then chlorosulphonated and treated with sodium hydroxide, and a second is treated with stannic chloride and paraformaldehyde in chlormethyl methylether followed by aqueous trimethyl amine and HCl; equal size pieces of the washed and dried films are superposed, sandwiched between aluminium foils, and pressed for two minutes at 160 DEG C. and 500 psi pressure.  (2). The treatment of the films is reversed, the first being acid-and the second alkali-treated, the dried films are hot-pressed at 400 psi for 30 seconds only.  (3). Similar treatments, with higher temperatures and pressures, are applied to films of high density polythene and to polytetrafluoroethylene reinforced with glass fibres respectively. (4). A high resistance bipolar unit enclosed with mercury contacts in a polymethylmethacrylate block is placed in series with a 20 ohm resistor across a sine-wave generator to demonstrate a different joint resistance for the two directions of the applied voltage, and is also connected similarly to a unidirectional pulse generator and exhibits differences of resistance according to the direction of the pulses and the orientation of the unit.  (5). A piece of anion-exchange film placed on aluminium foil has cured on it a syrup of aqueous p-phenol sulphonic acid and formalin which has been warmed until viscous.  (6). A film of chlorosulphonated polythenestyrene copolymer supported vertically between hollow glass clamps has diffused into it through the clamps sodium hydroxide solution coloured pink with phenol-phthalein and N-methyl piperazine coloured blue with pyronine B respectively; the diffusion can be observed by the dyes and when the reagents meet in the centre of the film the latter is removed and heated at 650 DEG C. for four hours to produce a bipolar anion-cation exchange component.  (7). A mixture of acrylamide, N1N'-methylene bis acrylamide, ammonium persulphate and sodium hydrosulphide is poured on to and cured on a portion of anion-exchange chlorosulphonated polythene-styrene copolymer film to produce a high resistance bipolar membrane.  (8). Two pieces of anion-exchange film and an interposed piece of cation-exchange film are pressed at 125 DEG C. and 400 psi for 10 seconds between aluminium foils to produce a radio frequency amplifying unit.