Patent GB-343889-A (GB)
Title: Manufacture of cellulose esters
IPC: C08B3/00
Filed: 1929-11-19
Abstract: Cellulose esters are made by treating an acyl cellulose, obtained by the action of an acid anhydride with the aid of a basic agent on cellulose, with an organic or inorganic esterifying agent in the presence or absence of an acid catalyst.  The crude solutions of the new esters may be spun directly.  The products are not soluble in the usual solvents but give solutions of very high viscosity in formic acid.  Basic agents include caustic alkali, bases such as pyridine or quinoline, and salts of weak acids with a strong base, e.g. sodium or potassium acetate.  The acid catalysts include zinc chloride, sulphuric or hydrochloric acid, halogens, acid halides, organic carboxylic or sulphuric acids, acid anhydrides, &c.  The following examples are given: (1) Bleached cotton is immersed in 5 per cent caustic soda lye for 2 hours at room temperature, pressed to 2-2 1/2 times the original weight of cellulose and, after drying, the whole is introduced into acetic anhydride and heated for 1 hour to 95-100 DEG  C.; the partially-acetylated material is then esterified by normal methods, e.g. with acetic anhydride, glacial acetic acid and sulphuric acid.  (2) Bleached cotton is immersed in 15 per cent caustic soda for 2 hours, pressed to 3-4 times the original weight and treated with acetic anhydride at 95-100 DEG  C. for 1 hour; the product, which contains about 1 1/2 acetyl groups is then formylated with 98-100 per cent formic acid containing 10 per cent of zinc chloride; after about 10 days at room temperature a clear, strongly viscous solution is produced which is mixed with ice-water to obtain a snow-white product soluble in formic acid, pyridine, chlorhydrin, a solution of phenol, benzene, aniline, aqueous acetone and hot acetic acid but insoluble in tetrachlorethane and chloroform.  Pyridine gives a viscous solution which yields clear, strong, stable films. (3) The preliminary acetylation is conducted as in (2) but in the presence of pyridine whereby a product substantially a diacetate is obtained; this is formylated by immersion for 20 hours at room temperature in 98-100 per cent formic acid containing 10-12 per cent of hydrochloric acid gas, yielding a clear, viscous solution from which the product is precipitated with ice-water.  The product is substantially a tri-ester and shows enhanced solubility over the product of (2) e.g. it is easily soluble in cold glacial acetic acid and in anhydrous acetone, and is partially soluble in tetrachlorethane when heated.  A smaller proportion of hydrochloric acid, e.g. 0,3-0,15 per cent requires 2-4 days and yields products similar to (2).  (4) A preliminarily acetylated cellulose as in (3) is formylated by immersion for about 7 hours in 98-100 per cent formic acid saturated with hydrochloric acid gas yielding a solution which may be spun directly into water or a solution of formic acid or sodium formate.  The precipitating bath may contain swelling agents e.g. formic acid, alcohol or a thiocyanate and softening agents, e.g. triacetin, triphenylphosphate or tricresylphosphate.  If not spun directly, the solution is neutralized with sodium formate to preserve its viscosity.  (5) Preliminarily acetylated cellulose as in (3) is introduced into a liquid containing 85 per cent formic acid saturated with hydrochloric acid gas and 10 per cent zinc chloride.  A clear solution is obtained after about 2 hours at room temperature, or 30-40 hours at 0 DEG  C., which solution can be spun and yields a product, substantially a diester, which is soluble in formic acid and pyridine but insoluble in glacial acetic acid and acetone.  Formic acid of 95 per cent strength yields a product containing about 2 1/2 acid groups.  (6) Cellulose pretreated with alkali as in (2) is treated with boiling acetic-anhydride for 1 hour and the product, after drying, is introduced into 100 per cent nitric acid.  After 16 hours at room temperature the solution is poured on to ice and the precipitated ester washed and dried.  It is soluble in acetone, nitrobenzene, and glacial acetic acid and yields films and threads less inflammable than those of nitrocellulose. Inflammability may be counteracted by tricresylphosphate &c.  (7) Preliminarily acetylated material as in (2) is introduced into a cooled mixture of equal parts of glacial acetic acid and 96-100 per cent nitric acid and left at room temperature.  After 48 hours a clear solution is produced which is mixed with ice-water. The product is soluble in pyridine but insoluble in acetone and has inflammability similar to that of acetyl cellulose.  The pyridine solution gives very strong, flexible films. By allowing the acetylating mixture to act for 4 days an acetone-soluble product is obtained.  (8) Chloracetyl cellulose, obtained by the action of chloracetic acid on cotton which has been swollen and thereafter impregnated with potassium acetate, is treated with a mixture of acetic and nitric acids as in (7).  At room temperature a clear solution is obtained after 6-10 days.  This is run gradually into ice-water and the precipitated ester is washed with cold, followed by hot water.  The product is insoluble in hydrocarbons, alcohol, ether, and chloroform but dissolves in hot glacial acetic acid and formic acid.  In pyridine it dissolves but gelatinizes.  Cold acetone gives a viscous solution which, on evaporation, yields solid, transparent and elastic fibres.  (9) Chloracetyl cellulose as in (8) is treated with 98-100 per cent formic acid containing 1 per cent hydrchloric acid and 10 per cent zinc chloride until acetone-solubility is attained.  The product has properties analogous to the nitric acid product of (8).  In place of acetic anhydride, other acylating agents, e.g. chloracetic anhydride, butyric anhydride, propionic and chloropropionic anhydrides, may be used in Examples 1-7. Specification 325,822, [Class 2 (ii), Cellulose &c.], is referred to.