US2033716A - Process of preparing fibrous esters of cellulose - Google Patents

Description

Patented Mar. 10, 1936 PATENT OFFICE 2,033,716 PROCESS OF PREPARING FIBROUS ESTERS OF CELLULOSE William 0. Kenyon and George P. Waugh,

Rochester, N. Y., assi Company, Rochester, New York No Drawing. Applica gnors to Eastman Kodak N. Y., a corporation of tion September 8, 1933,

Serial No. 688,623

3 Claims.

The present invention relates to the preparation in fibrous form of organic acid esters of cellulose, especially mixed organic acid esters in which the cellulose is pretreated with all or substantially all of the esterification ingredients except the catalyst, prior to its esterification.

Heretofore in processes for the preparation of organic acid esters of cellulose by a fibrous method the cellulose has been pretreated with a bath comprising a fatty acid and a catalyst preliminary to its esterification. Due to the large amount of fatty acid present the presence of a considerable amount of non-solvent is necessary in the esterification bath to assure non-solution of the ester formed. This disadvantage has been recognized in many cases in which there has been attempted correction by pressing or centrifuging oil or washing oi? the pretreatment liquid (for instance with non-solvent) which of course results in partial removal thereof. This latter procedure permits the use of less quantities of non-solvent than is the case when the pressing step is omitted. In some processes for the fibrous preparation of cellulose esters, probably due to the expense and trouble involved in the pretreatments ordinarily employed for this type of process, the pretreatment step was omitted entirely, the untreated cellulose being introduced directly into the esterification bath. In this latter procedure the cellulose is not as readily susceptible to esterification, especially in a fibrous esterification process in which the ester is not dissolved upon its formation, as the case where it is pretreated.

One object of our invention is to provide a pretreatment method for cellulose to prepare it for fibrous esterification in which any appreciable amount of organic acid is unnecessary thus permitting diminution of the amount of non-solvent ordinarily necessary to prevent solution of the cellulose ester formed. Another object of our invention is to provide a pretreatment in which substantially all of the esterification mixture except the catalyst is employed to penetrate the cotton so that only the addition of the catalyst is needed to promote the esterification. Due to the small amount of catalyst necessary compared to the large amount of conveying liquid which has penetrated the cellulose the catalyst may readily introduce itself to any portion of the cellulose thus tending toward a uniform action. A further object of our invention is to provide a pretreatment in which a comparatively large amount of pretreating liquid is employed thus assuring thorough penetration of the cotton fibers and providing a fluid mass which can, if desired, be

agitated by stirring or be readily flowed from one receptacle to another.

We have found that an organic acid ester of cellulose may be prepared by a process embodying all the above advantages in which cellulose is pretreated with a mixture of fatty acid anhydride, and an inert non-solvent and where necessary a small amount of a common solvent such as propionic or acetic acid to bring all the liquids into mutual solution. The esterification proper is then brought about by the addition of catalyst to the pretreatment mass. In the case of some non-solvents such as those with which the anhydride is compatible obviously the use of common solvent is unnecessary in the pretreatment bath. 1

The following examples illustrate fibrous esterification processes embodying our invention:

Example I 20 lbs. of cotton linters were pretreated for approximately 63 hours at a temperature of .approximately 40 C. with a mixture comprising 30 lbs. of acetic anhydride, 26 lbs. of propionic anhydride, 65 lbs; of a refined petroleum distillate having a boiling range of -72 C. and 8 lbs. of propionic acid. Some of the liquid was pressed off and llb. of sulfuric acid (sp. gr. 1.84) was added to the pressed off liquid which was then remixed with the cotton. 7 35 lbs. more of the petroleum distillate were added and the whole was maintained at 40 C. for 3 hours and then at approximately 53 C. for about 20 hours, accompanied by occasional agitation of the mass. The ester was removed from the bath, washed and dried and exhibited solubilities in the following solvents; ethylene chloride, chloroform, ethylene chloride-ethyl alcohol (90:10)

Example II 20 lbs. of cotton linters were pretreated for about 18 hrs. at 53 C. with a mixture comprising 16 lbs. of propionic anhydride, 36 lbs. of acetic anhydride, lbs. of a petroleum distillate having a 60-72 C. boiling range and 8 lbs. of propionic acid. Some liquid was separated off for instance by draining or pressing and .4 lbs. of sulfuri acid was mixed therewith whereupon the liquid was again added to the cotton. The temperature was raised to 53 C. over a period of about 5 hrs. and was maintained at that point for about 18 hrs. The ester was separated out in the manner employed in the previous example. This ester was found to exhibit solubilities similar to those of the product of Example I.

Example III 50 lbs. of cotton linters were pretreated for 16 hrs. at approximately 53 C. with a mixture comprising lbs. of butyric anhydride, 90 lbs. of acetic anhydride, 177 lbs. of a low boiling petroleum distillate and 22 lbs. of acetic acid. Esterification was induced by adding 1 lb. of sulfuric acid thereto in the same manner as before. The temperature was raised to 53 C. over a period of 5 hours and was maintained at that point for approximately 18 hours. The product, separated from the reaction mixture in the usual manner, was found to be soluble in ethylene chloride, ethylene chloride-ethyl alcohol (90:10) and chloroform.

Example IV 20 lbs. of cotton linters were pretreated for 16 hrs. at 53 C. with a mixture comprising 16 lbs. of propionic anhydride, 36 lbs. of acetic anhydride and 88 lbs. of benzene. 0.5 lb. of sulfuric acid was added in the same manner as in the previous examples and the temperature was raised to 53 C. over a period of 5 hrs. and maintained at that temperature for hours. The product, separated out as before, was soluble in ethylene chloride-ethyl alcohol (90:10).

Although our invention is particularly directed to esterification processes in which the saturated aliphatic hydrocarbons, either open chain such as ligroin, gasoline, petroleum ether, and Stoddard Solvent described in Bureau of Standards Bulletin, CS3-28, the use of some of which as non-solvents is disclosed in Minsk, Kenyon and Gray application Serial No. 671,900 filed May 19, 1933, or cyclic such as cyclohexane, are employed as the non-solvents it will be understood that it is also applicable to esterification processes employing other non-solvents such as benzene or other aromatic hydrocarbons, carbon tetrachloride or other non-solvent chlorinated hydrocarbons or higher boiling ethers such as iso-amyl ether, the use of the latter in fibrous esterification processes being disclosed and claimed in Malm and Fletcher Patent No. 2,000,602. As was pointed out above when a nonsolvent is employed which is compatible with the acid anhydride employed, the addition of fatty acid in the pretreatment bath is unnecessary. On the other hand the liquid petroleum hydrocarbons which exhibit the characteristic of in compatibility with acetic anhydride have comparatively high power of rendering an esterification bath non-solvent of the ester formed so that a smaller quantity thereof is as effective as a greater amount of another type of non-solvent. The homogenizing of a fibrous esterification bath in which a petroleum hydrocarbon is employed as the non-solvent by means of a lower fatty acid is the invention of Minsk, Kenyon and Gray and is disclosed and claimed in their application Serial No. 671,900, filed May 19, 1933.

Our invention is particularly adapted to the preparation of the lower fatty acid esters of cellulose such as cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose propionate and cellulose butyrate, however, it would obviously follow that it is also applicable generally to the organic acid esters of cellulose.

The esters prepared by our invention may be hydrolyzed to alter their solubility properties in any manner designed for the hydrolysis of cellulose esters in fibrous form, such as for instance in phenol and a basic nitrogen compound which is disclosed and claimed in Staud and Minsk Patent No. 2,000,620 or in a solution of zinc iodide or ferrous chloride in alcohol which process is disclosed and claimed in Staud and Murray Patent No. 2,005,383. By this hydrolysis step an ester such as primary cellulose acetate which is acetone-insoluble may be converted to the acetone soluble variety.

There are many catalysts which will promote the esterification of cellulose known in the art and it is to be understood that one of these may be employed in our invention instead of sulfuric acid which was employed in the processes disclosed in the examples.

We claim as our invention:

1. A process for preparing an organic acid ester of cellulose in fibrous form which comprises pretreating the cellulose, in the absence of a catalyst, with a mixture comprising a lower fatty acid anhydride, a liquid petroleum distillate which is essentially within a boiling range of 40-210" C. as the non-solvent for the ester to be formed and a lower fatty acid to homogenize the mixture, and thereafter causing esterification by adding a catalyst to the mass.

2. A process for preparing an organic acid ester of cellulose in fibrous form which comprises pretreating the cellulose in the absence of a catalyst with a mixture comprising a lower fatty acid anhydride, a liquid petroleum distillate which is essentially within a boiling range of 40-210 C. as the non-solvent for the ester to be formed and propionic acid to homogenize the mixture, and thereafter causing esterification by adding a catalyst to the mass.

3. A process for preparing an organic acid ester in fibrous form which comprises pretreating the cellulose in the absence of a catalyst with a mixture comprising acetic anhydride, a liquid petroleum distillate which is essentially within a boiling range of 40-210 C. as the non-solvent for the ester to be formed and a lower fatty acid to homogenize the mixture and thereafter causing esterification by adding a catalyst to the mass.

WILLIAM O. KENYON. GEORGE P. WAUGH.