Patent GB-212865-A (GB)
Title: Process for the production of viscose
IPC: D01F2/08
Filed: 1923-06-02
Abstract: 212,865. Lilienfeld, L. March 15, 1923, [Convention date]. Cellulose xanthates, and processes for making filaments, films, and other articles from; preparatory treatment of cellulose materials. - Viscose solutions are prepared while continuously or temporarily employing temperatures below 0 C., preterably temperatures 0 and -25 C. or lower, particularly between -3 and -15 C.; the cooling may take place during or before or after the treatment of the cellulose material with carbon disulphide, the essential condition being that the action of the disulphide proceeds wholly or in part before dissolution takes place, that is, before cooling begins. By cooling during the. sulphidizing and dissolving stages, particularly the latter, it is possible to conduct the process as a single operation, and such operation may even include the mixing of the cellulose with the alkali solution. By prolonging the cooling treatment, partial or complete separation of crystals or freezing may take place, but this in no way impairs the qualitv of the product and in many cases it is advantageous for such freezing to occur. Working in this manner, a substantial reduction in the duration of the process is effected, there is less degradation of the cellulose molecule and the effects of degradation that may have already occurred mav be neutralized, and in the case of artificial silk the ripening before spinning may be dispensed with; adopting alkali-cellulose as the parent material, then the usual mercerizing and ripening operation may be omitted, and the disintegration replaced by a simple loosening; the solutions obtained are coagulated by dilute inorganic and organic acids, salt solutions, or by alcohol, or by heat or steam. As an important advantage of the process it is found that the proportion of carbon disulphide may be reduced even to the proportion of 1/6 to 1/40 of a molecule of carbon disulphide to one molecule of cellulose, (C6 H10 O5), and the solutions so obtained are colourless, keep well, may be spun immediately, and do not give milk products on coagulation. The parent materials may be those ordinarily employed in viscose manufacture.; products obtained in coagulating solutions of cellulose in acids., particularly if coagulated before too great degradation has occurred; cellulose hydrate regenerated from waste viscoses, and artificial silk; bleached and unbleached celluloses; cellulose conversion products formed by mechanical disintegration with water; products obtained by treating cellulose with oxidizing or reducing agents, or by heating cellulose alone or in the presence of water, glycerine, or salts; mercerized cellulose, with or without subsequent washing with water, or treatment with dilute acid, and with or without subsequent or simultaneous treatment with bleaching or oxidizing agents; the celluloses and cellulose hydrates obtained on precipitating viscose solutions or solutions of cellulose, for example, in ammoniacal-copper and zinc chloride solutions, and strong mineral acids (for example, sulphuric, phosphoric, hydrochloric and arsenic acids) ; products obtained by treating cellulose with ammoniacal-copper or zinc chloride solutions, but not to the point of dissolution; hydrocelluloses; oxycelluloses; and especially cellulose when obtained in solution by treatment with alkali at low temperatures. For the treatment of the parent material three methods may for instance, be adopted : the cellulose &c. is converted into alkali-cellulose by treatment with 15-50 per cent lye, the excess of lye eliminated, as by centrifuging or pressing, and the resulting moist alkali-cellulose comminuted in a disintegrator, shredder, beater, etc.; alternatively, the cellulose may be treated from the first with a limited quantity of caustic soda lye, in which case the intermediate pressing is eliminated; or the parent material is mixed with dilute alkali solution, for instance caustic soda lye of 3-12 per cent strength, or the alkali cellulose prepared as above described may be treated with so much water or lye as will bring the alkali to the desired proportion and concentration. The mixture of these reacting-materials may contain from the commencement sufficient alkali to prepare a viscose solution of the desired degree of viscosity; alternatively, the necessary quantity of alkali may be added at a later stage. It is to be noted, however, that from the outset a solution of cellulose in alkali mav be used. When alkali-cellulose is employed, sulphidizing and solution are two separate operations. As regards the latter stages of the process, it may generally be stated that the following alternative methods are available :- sulphidizing and dissolution are both conducted at temperatures not substantially exceeding 2 C. and preferably between 0 and -25 C. or lower; or sulphidizing is conducted partly at temperatures above 0 C. and partly at the lower temperatures mentioned, while dissolution is effected wholly at these lower temperatures; or sulphidizing is effected wholly at temperatures above 0 C., say at 0-30 C., and dissolution at temperatures not substantially exceeding 2 C., thus as a particular case it is possible to sulphidize at 3 to -1 C. and to dissolve at -6 to -10 C. The several reagents may be mixed together in any sequence, for instance, the cellulose may first be mixed with carbon disulphide diluted if desired with benzene, light petroleum, &c., and the alkali then added, the mixture being finally brought to a temperature not substantially exceeding 2 C. The temperature to which cooling is to be carried depends on the strength of the alkali, on the proportion of carbon dieulphide employed, and on the chemical and physical properties of the parent material; that is to say, the effects associated with the employment of low temperatures show themselves sooner as the concentration of the lye is higher, for instance, with 10 per cent lye, solutions are obtained at 0 to -5 C., whereas with 6 per cent lye, temperatures -8 C. or even lower are necessary; and as regards the proportion of carbon disulphide, solutions are produced at a temperature of 0 C. when using a proportion of 20-40 per cent, at -2 to -5 C. with a proportion of 10 per cent, and at still lower temperatures with a proportion of 2 per cent; and according to the degree of degradation or opening-up of the parent material so the temperature may be varied, in the sense that the less degraded or opened-up material requires the greater degree of cooling. As a general guide cooling is continued until a sample shows complete dissolution or until a test film shows the desired clarity and strength. It is advisable to stir, knead or otherwise to agitate the mass during the cooling operation. The Specification includes a number of detailed examples. The solutions obtained by this process may be used in the production of artificial silk, cotton, staple fibre; artificial hair; films; plastic masses; coatings for paper, leather, textiles, etc.; dressings, sizings or fillings for fabrics or yarns; bookcloth; and artificial leather. Specification 212,864 is referred to. The Specification as open to inspection under Sect. 91 (3) (a) includes the employment of temperatures not substantially exceeding 2 C. This subject-matter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 205,898.