GB402055A - Improvements in or relating to the production of porous materials - Google Patents

Abstract

Porous masses made of or containing a cellulose carboxylic ester are subjected to saponification which may be partial or complete. The material may be made by dispersing, in a liquid or plastic mass of the cellulose carboxylic ester, solid, liquid or gaseous particles incompatible with the mass, treating the mass so as to set it, removing the dispersed solid or liquid if present, and finally saponifying the ester. The saponified material swells on immersion in water in a manner similar to the swelling of natural sponge, whereas the unsaponified material is more like pumice. It is preferred to disperse the pore-forming substance in concentrated and very viscous solutions of cellulose acetate or other cellulose carboxylic ester. Setting of the cellulose ester mass may be effected by evaporation of solvent, or by the action of a coagulating bath, or by cooling. The pore-forming substance may be rock salt, or a sulphate, sulphite, carbonate, or borate. The particles of the insoluble substance may be varied in size according to the size of the pores desired in the porous material. Setting of the plastic mass may be effected at the same time as the removal of the dispersed material or the two operations may be carried out separately. A solution of cellulose acetate in acetone may be coagulated with a liquid hydrocarbon and the dispersed solid removed subsequently by treatment with water. The extracting liquid may contain solvents or swelling agents for the cellulose ester. When the pores are formed by gas, fine bubbles may be passed rapidly into a viscous solution or melted mass of cellulose acetate. The gas may be produced by decomposition of a dispersed solid substance such as a carbonate by chemical treatment of the mass during or subsequently to setting. Finely divided sodium or calcium carbonate may be mixed rapidly into a concentrated solution of cellulose acetate in acetic acid such as an esterification liquor, the mass being then immersed in water. The size of the pores may be increased by reducing the external pressure before complete setting of the mass. If desired the cellulose ester may be worked up on rolls with the insoluble substance and with solvents. Pigments, fillers, and fibres may be incorporated. The masses may be formed into blocks or slabs and smaller masses cut from these to any desired shape, or the material may be shaped in moulds. In an example graded particles of crushed rock salt are dispersed in cellulose acetate solution. The mass is pressed into the desired shape and dried. The dried mass is extracted repeatedly with water, and then saponified by treatment with caustic soda for several hours.ALSO:Porous masses made of or containing a cellulose carboxylic ester are saponified wholly or partially. The porous material may be made by dispersing, in a liquid or plastic mass of the cellulose ester, solid, liquid or gaseous particles, treating the mass so as to set it, removing the dispersed particles, if solid or liquid, and finally treating with saponifying agent such as caustic soda. The saponified material swells in water like a natural sponge whereas the unsaponified material is more like pumice. Setting of the mass is effected by evaporation of solvent or by cooling, or by treatment with a coagulating liquid. The pore-forming substance may be rock salt, or a sulphate, sulphite, carbonate, or borate. The size of the particles is chosen with a view to the size of the pores desired. Setting of the mass may be effected at the same time as, or separately from, the removal of the dispersed material. Cellulose acetate solution may be coagulated with a liquid hydrocarbon and the dispersed solid removed subsequently with water. The extracting liquid may contain swelling agents for the cellulose ester. When the pores are formed by gas, fine bubbles may be injected into the viscous solution or melted mass, or produced by decomposition of a dispersed solid such as a carbonate by acid treatment. Sodium or calcium carbonate may be mixed with an esterification solution of cellulose acetate and acetic acid, the mass being then immersed in water. The size of the pores may be increased by reducing the external pressure before complete setting of the mass. The pore forming material may be worked up on rolls with the cellulose ester. Pigments, fillers, and fibres may be incorporated. The masses may be formed into blocks or slabs and smaller pieces cut from these to the desired shape, or the material may be shaped in moulds. In an example, graded particles of rock salt are dispersed in cellulose acetate solution. The mass is pressed to the desired shape and dried. The dried mass is extracted repeatedly with water, and then saponified with caustic soda.