GB303152A - Improvements in or relating to the preparation of solutions or plastic masses - Google Patents

Abstract

303,152. British Celanese, Ltd., (Assignees of Crooks, W. E., and Walton, C. D.). Dec. 29, 1927, [Convention date]. Plastic compositions containing cellulose derivatives; indiarubber &c. compositions.-Homogeneous solutions or plastic masses are produced from solids by pretreating the solids before applying the main portion of the solvent or solute to be incorporated' with the solid, with a substance in the vapour phase, such substance being either a solvent or solute for the solid and being the same substance. as the solvent or solute subsequently to be incorporated or readily miscible therewith. Alternatively, the substance used for the pretreatment may be applied in solution in a liquid inert to the solid under treatment, the solution being of insufficient concentration to produce solution of the solid. A solute is defined as a substance which dissolves in the solid as is the case, for instance, with plasticizers and cellulose derivatives. When the solid is pretreated with the vapour of a solvent or solute, the vapour may be admixed with gases, which should be inert towards the solid and should not form an explosive mixture with the vapour; thus, air is preferred but may be replaced or diluted with other gases, such as nitrogen, carbon dioxide or hydrogen. The pretreatment process is particularly suitable for the preparation of solutions or plastic masses containing cellulose esters or ethers, for example cellulose nitrate, acetate, formate, propionate, butyrate and methyl, ethyl or benzyl celluloses but may also be employed for those containing rubber, resins or the like. Suitable substances for the pretreatment comprise .acetone, alcohol, ether and ethylene dichloride, but any other solvents or solutes may be employed. In an example, air dried acetone-soluble cellulose acetate is exposed to a current of air saturated with acetone until the acetate has absorbed acetone, to the extent of 20-25 per cent of its weight. The product, which still retains the appearance of cellulose acetate but is damp to the touch, is then mixed with sufficient liquid acetone to make a solution containing, for example, 25 per cent of cellulose acetate. This solution may be used for the preparation of artificial silk or any other suitable purpose. Instead of pretreating the solid with the vapour of the solvent, the solvent may be employed diluted with an inert liquid, for instance, in the pretreatment of cellulose acetate with acetone, the latter may be dissolved in benzene, which must be present in sufficient concentration that the acetate is not dissolved. The procedure may be modified in order to prepare highly concentrated solutions, pastes, gels or other plastic masses directly, by exposing the solid, for example cellulose acetate, to the solvent vapour, for instance acetone vapour, under conditions such that the solvent vapour is alternately heated and cooled or compressed and reduced so as to produce intermittent condensation of the vapour in the mass of material being treated.