GB999587A - Cellulose ethers - Google Patents

Abstract

<PICT:0999587/C3/1> A process for preparing sheet-forming particles, fibres, films and other shaped structures of a cellulose ether, comprises forming a cellulose ether, dissolving the ether, introducing the ether into an acidic regeneration bath to precipitate the ether as a shaped structure, and treating the shaped structure with an aqueous salt solution containing a neutral salt and a basic salt, the concentration of the neutral salt being greater than that of the basic salt. The cellulose ether may be prepared by treating alkali cellulose, having a caustic content of less than 30% by weight, at 5-45 DEG C. in the solid state with 0.5-3.0 moles of etherifying agent per mole of anhydroglucose. The product may be dissolved in dilute caustic soda. The cellulose may be subjected to xanthation before, after, or simultaneously with etherification. The etherified or etherified and xanthated product may be aged, before precipitation and regeneration. The regenerating bath may contain sulphuric acid and sodium sulphate, or sulphuric acid, sodium sulphate, and zinc sulphate. The salt solution with which the precipitated shaped structure is treated, may contain a buffer, e.g. disodium hydrogen phosphate in presence of sodium sulphate. The treating solution, which neutralizes the acid in the shaped structure, may be maintained at pH 5-6. In one embodiment, fibres or films are formed by extrusion of the cellulose ether solution into the acid regenerating bath. In another embodiment, shear-precipitated sheet-forming particles are formed by precipitating the cellulose ether solution under such conditions of shear and coagulation that a "total shear value," R1s, of 3 t0 10,000 is provided. The "total shear value" is defined by the formula <FORM:0999587/C3/1> wherein Vp and Vs are viscosities in poises, of the precipitant and solution respectively, measured at their respective temperatures just prior to combining to form the precipitate; t is the time in micro-seconds during which the precipitate is deformable, and Rp is defined by alternative expressions related to the characteristics of the stirring device used, the particular expression depending upon whether the Reynold's number of the system is not more than 3350 (laminar flow) or exceeds 3350 (turbulent flow). If a tube precipitator (Fig. 14) is used instead of a stirring device, modified expressions for R1s are operative, related also to rate of flow of precipitating liquid and to the radius of the tube. The ethers to be precipitated may have D.S 0.1-0.7, and the properties of the precipitated structure may be modified by incorporating an additive, such as synthetic or natural fibres, dyes, pigments abrasives, resins, lubricants or antioxidants into the cellulose ether solution or into the regenerating bath. Many such additives are specified. The shaped structures, which are highly swellable in water, may be obtained in deswollen form by displacement of water by acetone, or by treatment with a strong salt solution. Examples describe the preparation of solutions of cyanoethyl cellulose xanthate, shear precipitation of cyanoethyl particles therefrom in baths of specified compositions, and extrusion of the solution into filaments; the preparation and extrusion of hydroxypropyl cellulose, carboxymethyl cellulose and cyanoethyl cellulose; and the extrusion into filaments of hydroxyethyl cellulose. Other cellulose ethers, mixed ethers, and ether-esters are specified. The products have a water adsorbency of at least 7 grams per gram. Shear precipitated particles may be formed into sheets by conventional paper-making techniques. Specification 868,651 is referred to.