Patent GB-516945-A (GB)
Title: Process for stabilising cellulose esters
IPC: C08B3/22
Filed: 1938-08-02
Abstract: 516,945. Stabilizing cellulose esters. AFAG FINANZIERUNGS AKT.-GES. Aug. 2, 1938, No. 22861. Convention date, July 31, 1937. [Class 2 (ii)] Organic esters of cellulose which have been prepared by esterifying cellulose according to the non-solvent or suspension method in the presence of a catalyst containing sulphuric acid radicals, are stabilized by treating the esters in at least two steps in the undissolved state with at least one treatment liquid containing at least one alcoholic body at a temperature which is raised at least once during the treatment but is never above 140‹C. The temperature increase is effected to a degree corresponding' to the diminution of the total quantity of catalyst residues contained both in.the cellulose ester and the treatment liquid. Suitable hydrolysing liquids are alcohols, ether alcohols, ester alcohols and ether-ester alcohols, a number of which are specified, and these may be used with diluents such as hydrocarbons, esters and etheresters of lower fatty acids, ethers and water. The alcohol and diluent may comprise an azeotropic mixture. It is necessary for the stabilizing bath to be renewed as soon as the concentration of sulphuric acid rises to a point which is harmful to the ester ; in the case of cellulose acetate stabilized by means of a lower alcohol, the concentration may be of the order of 0.1 per cent. up to 20‹C. and of 0.01 per cent. up to the boiling point. Under other circumstances, the conditions are verified by comparing the acyl indexes or the viscosities of the stabilized esters with the acyl index or viscosity of the same ester stabilized with non-hydrolysing agents, e.g., as in the process of Specification 488,707. In an example, (1) linters are pretreated with acetic acid and esterified in the presence of benzene. The product is divided into three parts, the first part A is stabilized with ethyl acetate, the second B, after washing with benzene, is boiled with methyl alcohol, and the third, C is washed, twice washed with methyl alcohol at 20‹C. and then extracted with methyl alcohol at the boiling point. The products A and C are of equal quality and superior to B. (2) Cellulose acetate prepared as in (1) is divided into five parts D-H. The first part D is stabilized with ethyl acetate. The second part E is washed twice at room temperature and once extracted at the boil with iso-propyl alcohol. The third part F is treated as for E but the iso-propyl alcohol is refluxed at the boil. The fourth part G is extracted twice cold and once at the boil with an azeotropic mixture of iso-propyl alcohol and iso-propyl acetate. The fifth part H is washed three times cold with ethyl ether and then refluxed with normal propyl alcohol. (3) Pretreated linters are esterified in the presence of butyl acetate and the product divided into four parts J-M. The first part J is washed twice with ethyl acetate and then extracted at the boiling point with ethyl acetate. The second part K is washed twice cold and three. times hot with normal propyl alcohol. The third part L is treated as K, using monobutyl ether of glycol. The fourth part M is washed twice cold. with normal propyl alcohol and then treated in a circulatory system con-' taining heating means and means for neutralizing sulphuric acid by introducing alcoholic soda.