Patent GB-212864-A (GB)
Title: Manufacture of cellulose solution
IPC: C08B1/08
Filed: 1923-06-02
Abstract: Solutions of cellulose are prepared by treating a body of the cellulosic class with aqueous alkali solution while maintaining a temperature not substantially exceeding 5 DEG C., and preferably at 0 DEG to -25 DEG C. or even lower, for such a time only, that the solution obtained will not substantially gelatinize when brought to room temperature, or will gelatinize at room temperature and again become liquid when cooled. By the use of low temperatures solutions of cellulose in alkalies are obtained without degradation of the cellulose molecule; in fact, if in the parent material the cellulose has been degraded by a preliminary treatment, it is found that such degradation is largely neutralized by subsequent solution under the conditions above specified.  As parent materials the following may be instanced:-bleached or unbleached cellulose of every kind; every kind of matter containing cellulose; conversion products obtained by comminuting cellulose in the presence of water; conversion products obtained by treatment with oxidizing or reducing bleaching agents, or by heating cellulose either alone or in the presence of water, glycerine, etc.; the conversion products obtained by treatment with hot or cold alkali lyes with or without subsequent washing, treatment with acid, and bleaching agents; the cellulose products separated from cellulose solutions whether these be in ammoniacal-copper or zinc chloride solutions, or strong mineral acids such as sulphuric, phosphoric, hydrochloric, arsenic &c. acids, or raw or purified viscose solution; cellulose conversion products obtained by treating cellulose, hydrocelluloses, cellulose hydrates, &c. with solvents, but not to the point of dissolution; hydrocelluloses obtained by treating cellulose with dilute acids, or by drying in the presence of acids, or by treating with strong sulphuric acid of 50 DEG B<\>ae, gaseous hydrochloric acid, or chlorine; denitrated cellulose nitrate, and saponified cellulose acetate, formate, etc.; oxycelluloses; the partly-alkylated products soluble in alkali obtained according to the process described in Specification 177,810; and waste viscoses. The cellulosic material and the alkali may be mixed at the low temperature, or at room temperature or above and cooled subsequently. The cooling may be continued until freezing or crystallization occurs; in some cases such freezing &c. is advantageous.  It is advisable, during the cooling period, to keep the mass in movement. As regards the strength of the alkali solution, it is found that a concentration as low as 2 per cent is sufficient to produce incipient solution, a concentration of 3 per cent exhibits an advanced degree of solution, which is maintained for increasing concentrations to 16 per cent and higher; it is preferred, however, to use concentration between 4 and 10 per cent.  The temperature to be employed depends on the strength of the alkali solution and on the character of the parent material, in the sense that solution is obtained at higher temperatures with greater concentrations of alkali and according as the cellulose has suffered greater degradation; thus, for instance, mercerized sulphate-cellulose that has been pressed, comminuted, washed, and treated with dilute acid, is found to dissolve in soda lye of 4 per cent strength at 9 DEG  to 11 DEG  C., of 8 per cent strength at 8 DEG  to 9 DEG  C., and in 10 per cent lye at 5 DEG  to 7 DEG  C.; if, however, the parent materials have suffered greater degradation as by the recovery from cellulose solutions, then 10 per cent lye will effect solution at 0 DEG  to 5 DEG  C.  To ensure useful technical results it is in many cases necessary to cool further after complete solution has apparently taken place.  It may therefore be stated as a general rule guiding temperature, that perfect results are obtained readily at temperatures between 5 DEG and 15 DEG  C.  Lower temperatures are unnecessary, but entail no deleterious consequences.  Cooling if unduly prolonged is likely to lead to a thickening of the solution, which becomes gelatinous and muddy. The solutions may be worked up into technical products either in the cold or at room temperature.  They can be precipitated by salts, acids, alcohols, &c., or they may be coagulated by heat. Their stability at room temperature depends on the content of cellulose and the strength of the lye, the temperature to which they were subjected during the cooling operation, but especially the duration of the cooltreatment; many are very durable, while of the others, some give irreversible jellies and some reversible jellies, that is, they liquefy on cooling.  The solutions may be used in the manufacture of artificial silk, cotton, hair, etc., films, plastic masses, coatings, dressings, fillings, and sizes, book-cloth, and artificial leather; the coagulated masses may be used in the manufacture of cellulose esters &c.  The Specification contains a large number of detailed examples.  The Specification as open to inspection under Sect. 91 (3) (a) is not limited as regards the duration of the low-temperature treatment; and it also includes the plastic and gelatinous transition products passed through before complete solution is attained, and also the jellies into which the solution is converted, for instance, by too long exposure to the low temperature, which products are suitable as dressings or fillings, as substitutes for parchment paper and vulcanized paper and as binding agents.  Specification 17501/02 is also referred to.  This subject-matter does not appear in the Specification as accepted.