Patent GB-893822-A (GB)
Title: Improvements relating to the production of aqueous cellulose gels and sols
IPC: C08B1/00
Filed: 1959-02-12
Abstract: A cellulose gel or sol is produced by treating cellulose with an aqueous solution containing an iron-tartaric acid-alkali metal complex in which the iron is in the ferric state (see Group IV(b)), an excess of alkali metal hydroxide and an excess of alkali metal tartrate, the cellulose being first intimately mixed with a proportion of the solution which is insufficient for the immediate gelling of the cellulose, the mixture being then allowed to stand to ripen, with or without further agitation and kneading, until a uniform gel is obtained and the gel being then intimately mixed with such a proportion of aqueous alkali metal hydroxide solution as to produce a gel or a sol containing the desired concentration of cellulose.  The cellulose may be a natural or a regenerated cellulose or a ripened alkali cellulose.  The cellulose is preferably first mixed in the presence of an alkali metal hydroxide solution with a complex of moderate dissolving power and the mixture then mixed with a complex of greater dissolving power.  The proportions of iron, tartaric acid and alkali metal in the complex may be such that, for every gram atom of iron, the complex contains 1-3 mols. of tartaric acid and up to 6 gram atoms of an alkali metal, the concentration of the solution being 100 to 500 g/litre and the concentration of free alkali metal hydroxide corresponding to a solution of 1-5 normal strength.  The proportion by weight of complex to cellulose may be between about 5:1 and 0,2:1, preferably about 1:1.  Uniform permeation of the cellulose with relatively small quantities of the treating solution without immediate reaction is essential and can be promoted by the addition of small proportions of surface active substances used as mercerizing assistants, e.g. fatty acid-, fatty alcohol-, alkyl- or aralkylsulphonates or sulphates.  The treating solution may contain 5 to 20%, based on the weight of the cellulose, of compounds which promote swelling of cellulose in alkaline liquor, for example, aqueous solution of sodium hydroxide, examples of such compounds being urea, thiourea, acetamide, biuret, formamide or dimethyl formamide.  The proportion of the surface-active and/or the swelling agent may be up to 25% by weight, preferably 5-20% by weight, calculated on the cellulose.  The complex may be produced wholly or partly before or during the gelatinizing of the cellulose in the reaction mixture.  The complex solution may be made from tartratoferric acid.  The complex may be produced by combining an iron salt, an alkali metal tartrate and an aqueous alkali metal hydroxide solution, the solution therefore containing foreign ions, the isolation of the tartrato-ferric acid being omitted.  The solution of the complex may be mixed with the cellulose in the presence of a portion of the alkali metal hydroxide normally to be added for dilution.  In addition to using a single complex containing the previously stated proportions of tartaric acid, alkali metal and iron, it has been found particularly advantageous to use a mixture of a complex containing, for each gram atom of iron, 1 mol. of tartaric acid and 1 gram atom of alkali metal and a complex containing, for each gram atom of iron, 3 mols. of tartaric acid and 6 gram atoms of alkali metal.  In an example, 1 kg. of cotton linters hydrolytically degraded to a DP of about 400 are kneaded with 1170 cc. of a solution containing 300 g./l. of the sodium salt of tartrato-ferric acid, 40 g./l. of free sodium hydroxide and 35 g./l. of free sodium tartrate and these are then slowly added with continued kneading 1170 c.c., of a solution in which the proportions of the above constituents are 480, 120 and 35 g./l.  The mixture is allowed to stand for 24 hours at room temperature and 1170 c.c. of 3,4 N sodium hydroxide solution are then slowly incorporated in the mixture.  After allowing the mixture to stand for a further 15 hours, a further 1170 c.c. of 3,4 N sodium hydroxide solution is incorporated in the mixture and finally 10,5 litres of 3,4 N sodium hydroxide solution are added to produce a transparent viscous liquid containing about 6% of cellulose.  The finished gels and sols are permanently stable when stored with protection from direct sunlight.  Cellulose may be precipitated from them by the addition of aqueous solutions of acids.ALSO:Tartrato-ferric acid, which may be used for the production of cellulose gels and sols (see Group IV (a)), is prepared by adding an aqueous solution of ferric nitrate to an aqueous solution of sodium hydrogen tartrate and sodium hydroxide at 70 DEG C.-80 DEG C. The precipitate of tartratoferric acid formed is washed successively with water and methanol and dried at 50 DEG C.  An aqueous solution of the sodium salt of the acid is prepared by kneading the TF acid and sodium hydrogen tartrate with a small proportion of water to form a paste which is then heated to 60 DEG C.