GB305096A - - Google Patents

Abstract

305,096. Ruth-Aldo Co., Inc., (Assignees of Barthelemy, H. L.). Jan. 30, 1928, [Convention date]. Drawings to Specification. Grant of Patent opposed. Cellulose acetates are made by a complete process comprising oxidation of cellulose, in the form of cotton fibres, linters or pulp, by means of a direct oxidizing agent in a solution containing a moderating agent in the presence of preferably a weak base, (see Specification 282,794); pretreatment with at least 50 per cent of the weight of the cotton &c. of hot acetic acid vapours preferably containing a small amount of halogen, (see Specification 282,788 and 303,134); acetylation by addition of a succession of at least four complete acetylating baths each comprising acetic anhydride, acetic acid and a catalyst such as sulphuric acid either alone or mixed with halogen or an oxidizing agent, (see Specifications 282,788, 282,793 and 303,135), the baths being so arranged as to maintain the temperature between 18-26‹ C. during the earlier stages up to the obtaining of a product having an acetyl value of 25 per cent or thereabouts, while in the later stage for the completion of the acetylation the temperature is allowed to rise to preferably 55-65‹ C.; saponification by a two stage process, comprising the addition of an aqueous solution of formic or acetic acids containing hydrochloric water to destroy the excess of anhydride, followed by a fresh quantity of an aqueous solution of formic or acetic acids containing hydrocholric acid with or without hydrofluoric acid, (see Specifications 282,789 and 303,098), whereby any sulphuric esters are destroyed and an acetylated product of the desired solubility is obtained; precipitation of the acetate in water preferably containing a salt or other flocculating agent, followed by washing and drying. The process may be carried out in rotary apparatus, (see Specifications 282,791 and 303,099). As regards the acetylation step of the process, the composition of the several baths is such that the catalyst is added in small but progressively increasing quantities, and the acetic anhydride is progressively decreased until the final stage when the bulk is added; by the addition of halogen in the early stages of the acetvlation, the formation of cellulose sulphates is diminished; the presence of an oxidizing agent leads to the production of cellulose acetates free from colour and particularly suitable for the manufacture of plastics and artificial silk. In an example, cotton linters, boiled in an autoclave with weak soda lye and sodium resinate is immersed in an aqueous solution comprising caustic soda, marseilles soap, and hydrogen peroxide, washed, centrifuged and dried, after which it is introduced into apparatus of the type described in Specifications 282,791 and 303,099 where it is treated with acetic acid vapour and then with acetic acid containing dissolved chlorine gas sprayed in through a centralized spray; acetylation is effected by spraying into the apparatus in succession a series of five acetylation mixtures each composed of glacial acetic acid, acetic anhydride, and sulphuric acid with the addition of chromic acid and bromine to the first and second acetylation mixtures respectively the temperature being controlled in the manner indicated above throughout the acetylation process; the acetate is saponified by a two stage process comprising addition of aqueous acetic acid to destroy the surplus acetic anhydride followde by aqueous acetic acid containing hyrochloric and hydrofluoric acids and the acetate is then precipitated by a dilute solution of sodium bicarbonate and washed with water before drying.