US2002674A - Method of treating cellulose acetate - Google Patents

Description

Patented May 28, 1935 UNITED STATES METHOD on TREATING oELLULos ACETATE Richard Miiller. and Martin Schenck, Mannheim, and Wilhelm Wirbatz, Mannheim-Waldhof, Germany, assignors to C. F. Boehringer & Soehne G. in. b. H., Mannheim-Waldhof, Germany No Drawing. Application June'lf i, 1930, Serial No. 461,636. In Austria June 21, 1929 ll Claims. (01. 260-102) Our invention'refers to .a treatment of fibri form acetyl celluloses or cellulose acetates of the kind which dissolve in chloroform, whereby I the solubility of these compounds in acetone is affected me favourable manner.

As is well known to those skilled in the art, when cellulose is acetylized, there is first formed a primary product of acetylization which, before being fit for use in the production of artificial silk and other materials ,must first be converted into a secondary product containing less acetic acid and dissolving in acetone. The primary product, While being insoluble in acetone, is soluble in chloroform either completely or incompletely.

It is to these primary fibriform products which dissolve in chloroform eithter partly or totally that reference is had in the following specification and in the claims affixed thereto. They are little adapted for technical uses. We have now found that the solubility of these primary products can be influenced favourably by acting thereon with comparatively concentrated and strong acids, if care 'is taken to suppressby suitable additions the decomposing and dissolving effect 'of the acids. By this treatment the products are not aifected invany unfavourable manner and their fibrous structure is not destroyed.

We have found that by adding to the reaction mixture a salt, an ester or other inorganic or organic substances which are inert with respect to the cellulose acetate and the acid and are highly soluble in the acid, in such proportion as to prevent the cellulose acetate from dissolving during its conversion to the acetone soluble form, so that by exerting a salting out or precipitating effect on the acetyl cellulose with or without a simultaneous reduction of the dissociation of the acids, they prevent the acetyl cellulose from being dissolved, the action of the concentrated acids can be nicely regulated. Salting out is a Well-known phenomena which is produced by highly soluble salts. It is defined by Perry (Chemical Engineers Handbook, Mc- Graw Hill 00., 1934, page 564) as follows:

When an electrolyte (salt) is added to an aqueous solution of a non-electrolyte, as hydrogen, ether, or succinic acid, the solubility of the latter is greatly diminished. The mutual solubility of two liquids such as ether and water is reduced by the addition of such a salt as sodium chloride or sodium sulfate. This phenomenon is called the salting out effect In accordance with the mode of proceeding in each individual case including the character of the acids and additions used, their concentration and. relative proportions, the temperature etc. the productwill after a predetermined periodbec'ome solublein acetone either completely or incompletely.

Example 2 If a similar material is treated during some days at ordinary temperature with a 95% nitric acid saturated with ammonium nitrate, the product has become soluble in acetone while its fibrousstructure has not been changed.

Example 3 Fibrous cellulose acetate soluble in chloroform is introduced into a mixture of 9 parts by volume of a 96% phosphoric acid, 1 part of a 96% sulfuric acid and 23 parts cyclohexanol acetate. After the lapse of several days the product has become soluble in acetone. The reaction can be expedited by slightly heating the mixture.

Example 4 Fibrous cellulose acetate soluble in chloroform is treated at ordinary temperature during two days with a mixture of 10 parts by volume of a 96-97% phosphoric acid and 1'7 parts by volume cyclohexanol acetate with the result, that the acetyl cellulose has become soluble in acetone.

Example 5 Fibrous cellulose acetate soluble in chloroform is introduced into a mixture of 80 parts of a 96-97% phosphoric acid and 16 parts ammonium sulfate. After the lapse of 2-3 days the product has become soluble in acetone.

Other buffer salts which produce a salting out effect and which are useful in our process, for preventing the cellulose acetate from dissolving in the acid until the acetone-soluble stage is 55 reached, are potassium nitrate and calcium nitrate.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

We claim:-

1. The method of treating fibriform cellulose acetate soluble in chloroform but insoluble in acetone to render it soluble in acetone and yet preserve its fibrous structure, which comprises subjecting said acetate in solid fibrous form to a conversion bath of a concentrated mineral acid substantially saturated with a highly soluble buffer substance inert towards both the acid and the acetate but producing a precipitating effect on the acetate and acting to prevent the dissolving of said acetate by said bath, the action of the bath being continued until the acetate has been rendered soluble in acetone.

2. The method of claim 1 wherein said substance is a highly soluble inorganic salt.

3. The method of claim 1 wherein said substance is a nitrate.

4. The method of claim 1 wherein said substance is an ammonium salt.

5. The method of claim 1 wherein said substance is a sulfate. 1

6. The method of treating fibriform cellulose acetate soluble in chloroform but insoluble in acetone to render it soluble in acetone and yet preserve its fibrous structure, which comprises subjecting said acetate in solid fibrous form to a conversion bath of a concentrated mineral acid substantially saturated with a salt inert towards both the acid and the acetate but producing a precipitating effect on the acetate and acting to prevent the dissolving of said acetate by said bath, the action of the bath being continued until the acetate has been rendered soluble in acetone, said salt being selected from the group consisting of calcium nitrate, potassium nitrate, ammonium nitrate, ammonium sulphate and secondary ammonium phosphate.

7. The method of claim 6 wherein said substance is secondary ammonium phosphate.

8. The method of claim 6 wherein said substance is ammonium nitrate.

9. The method of claim 6 wherein said substance is ammonium sulphate.

RICHARD MI'JLLER. MARTIN SCHENCK. WILHELM WIRBATZ.