Patent GB-1188160-A (GB)
Title: Improvements in and relating to the Production of Film- or Filament-Like Porous Membranes
IPC: H01M4/86
Filed: 1967-07-24
Abstract: 1,188,160. Porous membranes. KALLE A.G. 24 July, 1967 [26 July, 1966], No. 33855/67. Heading B5B. [Also in Division C3] A process for the production of a film or filament-like porous membrane having a plurality of evenly distributed capillaries of almost equal size and form and being located substantially perpendicular to the surface of the membrane, by the formation of a polyelectrolyte gel from a polyelectrolyte sol by means of opposed ions diffusing from an electrolyte solution into the sol and forming a difficultly soluble polyelectrolyte salt, comprises generating a relative movement between the membrane being produced and the electrolyte whereas no relative movement is allowed between the membrane and the polyelectrolyte sol. The membrane may be in the fom of a sheet or in the form of a tube, fibre or hollow filament. The resulting membrane is preferably subjected to a consolidation treatment in which the water is first removed by an organic solvent and subsequently a polymer or polymerizable monomer is incorporated. In the preferred use of monomers, polymerization may subsequently be initiated by means of suitable accelerators. In the continuous method (preferred for tubes, fibres and hollow filaments) the polyelectrolyte sol is continuously extruded into the electrolyte in the form of a sheet, hollow filament, fibre or tube and the gel produced continuously drawn off, the electrolyte being moving or still, and the resulting membrane consolidated continuously. After the polyelectrolyte sol has been shaped into the desired form, e.g. by extrusion through a slot die or spinning head, it may be passed through the electrolyte solution without a support, the solidified gel being supported and transported by rollers, or may be applied to a support and passed through the electrolyte solution while upon and in contact with said support, suitably an endless metal band support which is passed into the electrolyte solution at an angle of introduction of only a few degrees with respect to the surface of the liquid. Alternatively, the polyelectrolyte sol may be formed on a former body, e.g. a rod, sheet or plate, introduced into the electrolyte on the said body and then further passed through the electrolyte solution after detachment from said body. Suitable polyelectrolytes are alginates, polyacrylates and copolymers of acrylates and/or substituted acrylates with other polymers or cellulose derivatives, as for example carboxymethyl cellulose or cellulose xanthate. Preferably the alkali metal salts of these polyelectrolytes, particularly their sodium salts, are used or their ammonium or amine salts. The solvent used for the polyelectrolyte salts is water and the preferred concentration of polyelectrolyte in the aqueous solution is from 0À25% to 5% by weight, the pH value of the solution being between 3 and 7. As opposed ions there are primarily used bivalent cations, e.g. of copper, zinc, cobalt, iron, nickel or cadmium. Instead, the cations of lead, calcium, strontium, barium or of lanthanum or cerium may be used. Water-soluble salts such as nitrates or acetates of the above-named cations and the chlorides of calcium, strontium, barium, lanthanum or cerium are employed. The solutions are generally 0À5 to 2 normal. Discontinuous operation (preferred for sheet-like porous membranes) may be effected by carefully covering a still polyelectrolyte sol with the electrolyte and producing a circulating movement in the latter by means of a blade agitator which moves the entire liquid as uniformly as possible. Stirring may be increased with increase of the thickness of the membrane. The gel so made is consolidated in known manner. The isoporous membranes from the metal salts of the polyelectrolytes generally contain more than 95% water and correspondingly less than 5% solids, and are thus very mechanically sensitive. For stabilizing the membrane, the water is replaced by a resin or metal. Examples relate to the production of films of copper alginate and sodium alginate, a porous filament of copper alginate and a hollow filament of copper alginate. Membranes so made are useful as electrodes in electrochemistry and may also be used as filters. Typically their pore diameters are in the range of several microns to several multiples of 10 microns.