Patent GB-489468-A (GB)
Title: Improvements in or relating to the production of porous materials
IPC: D06M15/05
Filed: 1937-10-27
Abstract: Composite porous material is obtained by coating a base material with a liquid or semiliquid composition having a basis of a cellulose ester or ether dissolved in a solvent medium which is substantially entirely organic and which contains distributed therein particles of a solid substance which is soluble or which is capable of evolving a gas, and thereafter setting the composition and either dissolving out the particles of solid or causing them to evolve a gas.  The treatment, e.g. with acid, for producing gas bubbles may be effected during the setting of the composition and before setting is completed.  The process may be modified by preparing a film or sheet of the cellulose derivative containing the solid particles, attaching the sheet to a base material, and then treating the composite article so as to dissolve out the solid particles or cause them to evolve a gas. The base material may be a fabric of cotton, flax, wool, hemp, ramie, silk, or artificial silk, and it may be in the form of gauze, canvas, or duck.  Felt from animal or vegetable fibres, paper, cardboard, asbestos board, wood veneer, or building board may also be used as base material.  The cellulose ester or ether composition may be set by evaporation of volatile solvent, or by treatment with a setting liquid such as a liquid hydrocarbon. Porous cellulose ester coatings may be subjected to saponification treatments to obtain products which swell like a sponge on immersion with water.  The pore-forming solid may be rock salt, sodium sulphate, carbonate, borate, sulphite, bisulphite, bicarbonate or formate, potassium carbonate or bicarbonate, ammonium carbonate, bicarbonate, benzoate, cyanide, nitrite or sulphite, magnesium sulphate, barium nitrite, calcium oxalate or manganese oxalate.  The agent employed for removing the solid particles or causing evolution of gas may contain a swelling agent for the cellulose derivative to assist penetration. The cellulose derivative composition may contain fillers such as cork, sawdust, shavings, clay, asbestos, cotton, flax, hemp, ramie, silk, and artificial silk fibres.  For colour effects the fibrous fillers may be coloured differently from the mass of the composition, e.g. by cross-dyeing methods.  The compositions may be applied to the base material by flowing or casting.  Both sides of the base material may be coated.  In an example, a cotton fabric is coated with a solution of cellulose acetate in acetone containing small particles of rock salt in suspension.  The coated fabric is dried and then washed with water to remove the rock salt.  The porous coating is then saponified to obtain a highly absorbent product. In another example, cotton fabric is coated with a cellulose acetate solution containing ammonium carbonate particles.  The fabric is dried and heated until the salt has decomposed.  The products may be used for insulating walls, pipes, refrigerators, and electrical appliances. Fabrics provided with sponge-like absorbent coatings of porous cellulose, obtained by saponification of the cellulose ester coatings, are useful as bath rugs, floor coverings, wash cloths, towels, bath robes, and other garments.  The Specification as open to inspection under Sect. 91 comprises also the use of cellulose derivative compositions containing liquid poreformers.  This subject-matter does not appear in the Specification as accepted.