US2066571A - Process for the fibrous esterification of cellulose employing homogenizers - Google Patents

Description

Patented Jan. 5, 1937 UNITED STATES PATENT OFFICE PROCESS FOR THE FIBROUS ESTERIFI- OATION F CELLULOSE EMPLOYING HOMOGENIZERS Louis M. Minsk, William O. Kenyon, and Harry Le B. Gray, Rochester, N. Y., assignors, by mesne assignments, to Eastman Kodak Company, Jersey City, N. J., a corporation of New The present invention relates to a process of esterifying cellulose in fibrous form in a bath in which an aliphatic or alicyclic hydrocarbon is employed as the non-solvent and a homogenizer is present to assure compatibility of the constituents of the bath.

Among the most efiective non-solvents known for the fibrous esterification of cellulose are the saturated hydrocarbons either aliphatic or alicyclic such as hexane or heptane mixtures or cyclohexane.

Some of these non-solvents are known under various names such as ligroin, petroleum ether, Stoddard solvent, kerosene, gasoline, naphtha etc. In cases where these saturated hydrocarbon nonsolvents are employed for esterifying cellulose the amounts necessary to assure insolubility of the resulting ester in the esterification bath are much less than is the case with the non-solvents which are ordinarily employed. However, these nonsolvents suffer the disadvantage that their mixture with the fatty acid anhydrides are heterogeneous especially in those cases where hydrocarbons having a high boiling range are employed. This is true even though a quite small amount of fatty acid might be present.

It is possible to prepare a cellulose ester in an esterification bath in which an aliphatic hydrocarbon is employed as the non-solvent in which no homogenizer is employed however the esterification is not uniform, the cellulose is severely degraded and the product, instead of being in fibrous form as should be the case in a fibrous esterification process, is usually in the form of a powder which is worthless for the preparation of film or sheets. By our process on the other hand an aliphatic hydrocarbon may be employed as thenon-solvent but the esterification is uniform and the product is substantially undegraded and is valuable commercially.

One object of our invention is to provide a process for the fibrous esterification of cellulose in which a saturated hydrocarbon may be employed as the non-solvent and in which the bath is homogeneous. Another object of our invention is to provide a process for the fibrous esterification of cellulose embodying all the advantages inherent in the use of a saturated hydrocarbon but in which all the reagents therein are compatible so that a uniform esterification of the cellulose is assured and an undegraded product which may be employed for the manufacture of sheets or film is obtained.

We have found that a fibrous esterification bath in which a saturated hydrocarbon is the non-solvent, may be rendered homogeneous by the addition thereto of an homogenizing agent. We have found that the lower fatty acids or the ethers when added in a substantial amount will homogenize the mixture of reagents which go to make up a fibrous esterification bath. Aromatic hydrocarbons such as benzene, toluene or cymene and halogenated hydrocarbons such as ethylene chloride or the like also find use as homogenizers in accordance with our invention, the use of the aromatic hydrocarbons as homogenizers being disclosed and claimed by Yackel and Kenyon in their application Serial No. 671,899, filed of even date and the use of chlorinated hydrocarbons as homogenizers is disclosed and claimed by Malm and Fletcher in their application Serial No. 671,901, filed of even date.

In a fibrous esterification process in which a saturated hydrocarbon is employed as the nonsolvent, a surprisingly small proportion of that hydrocarbon is necessary to render the esterification bath non-solvent of the cellulose ester formed, however, the non-solvency of this liquid is so pronounced that it extends even to constituents of the esterification bath. By the present invention the effectiveness of the saturated hydrocarbon to induce non-solvency of the cellulose ester by the esterification bath may be ultilized and a uniform undegrading esterification of the cellulose is assured.

The following table shows the amount of the particular homogenizer which is necessary to assure homogeneity in the given esterification bath. Obviously in instances where a difierent ratio of anhydride to hydrocarbon non-solvent is used, the amount of homogenizer may differ from that given, however, that amount will be determined by the effectiveness of the homogenizer. For example 6 parts of acetic acid would be'required where only parts of propionic acid (by volume) would be sufficient to homogenize an esterification bath. The parts given in the table are all based on volume.

Amount of homogenizer Saturated Acetic anhydrocarbon hydride Egg??? effect Parts Parts 2/0 5 parts benezene. 20 10 5 parts toluene. 20 10 6 parts xylene. 20 10 6 parts ethyl ether. 20 10 5 parts propionic acid. 20 10 6 parts acetic acid.

In some esterification processes acetic or propionic acid might be present and in that case it is only necessary to add sufiicient acid or other homogenizer to supplement the efiect of the organic acid present if it is present in insufficient amount to assure homogeneity of the esterification bath.

The following examples illustrate the application of our invention to the preparation of organic acid esters of cellulose.

Example I 20 lbs. of refined cotton linters was pretreated for 16 hrs. at room temperature with 140 lbs. of propionic acid containing 1.5 lbs. of mixed catalyst (1 part by volume concentrated H2SO4I3 parts 95% HaPOl). The mass was then pressed until the total weight of linters and acid was lbs. The esterification was then promoted by adding a mixture of 50 lbs. of acetic anhydride and lbs. of ligroin to the pressed mass and the temperature was raised to 53 C. over a period of 2 hours and was maintained at that point until a sample showed solubility in ethylene chloridealcohol (:10). The ester was then separated .from the reaction mixture, treated with hot water,

washed to neutrality and dried.

Example II 25 lbs. of purified cotton linters was pretreated for 16 hrs. at room temperature with a mixture of 25 lbs. of glacial acetic acid and 20 lbs. of a low boiling petroleum distillate. The esterification was then promoted by the addition at 20 C. of a mixture of 30 lbs. of butyric anhydride and 40 lbs. of acetic anhydride with 1.5 lbs. of mixed catalyst (see Example I) and 68 lbs. of a low boiling petroleum distillate. The temperature was raised to 40 C. over a period of 2 hours and was there maintained for 48 hrs. or until the reaction is completed. The ester was then separated from the reaction mixture, washed with hot water and then to neutrality with cold water and dried at 50-60 C. It was found to be soluble in ethylene chloride-ethyl alcohol (:5). When coated from this solution it gave skins of good flexibility.

Example III ride-alcohol (85:15)

Example IV 50 lbs. of cotton linters was pretreated with lbs. of a mixture composed of 4 parts of propionic acid and 1 part of acetic acid for 4 hours at F. after which it was cooled to 70 F. A mixture of 150 lbs. of acetic anhydride, 125 lbs. of a petroleum hydrocarbon having a boiling range of ISO-210 C., 125 lbsyof ethyl ether and 1 lb. of concentrated sulfuric acid was added to the pretreated mass and the temperature was permitted to rise from 70 to 120 F. over a period of 5 hours. The whole was then kept at 120 F. until a sample showed complete solubility in a mixture of 95 parts of ethylene chloride and 5 parts of methyl alcohol by volume. This esterification required about 10 hours. The fibers were then centrifuged and washed with ether. The non-solvent retained by the fibers was removed by boiling the fibers with water after which they were dried.

Example V 25 lbs. of cellulose was pretreated with a mixture of '75 lbs. acetic acid, 32 lbs. of Stoddard solvent and 25 lbs. of toluene for 18 hours at room temperature. The esterification Was promoted by adding a mixture of lbs. of acetic anhydride, 132 lbs. of Stoddard solvent, 116 lbs. of toluene and 1.5 lbs. of mixed catalyst (3 volumes phosphoric: 1 volume sulfuric acid). The temperature was raised to 40 C. over a period of 2 hours and was maintained at that point until the reaction was complete which required about 27 hours. The resulting cellulose acetate was washed and dried. It was found to be soluble in methylene chloride-ethyl alcohol (90:10 by volume). Stoddard solvent is a commonly known petroleum distillate having a boiling range of 300-410 F., the specifications of which are disclosed in a Bureau of Standards bulletin, Commercial standard C. S. 3-28 (1929). The pretreatment of cellulose with a fatty acid and a non-solvent is described and claimed in Yackel and Kenyon application, Serial No. 671,898, filed of i even date.

Our process is adapted to cellulose esterification processes generally for the preparation of organic acid esters of cellulose. Other esters than those of the specific examples which may be produced by our process are cellulose propionate, cellulose butyrate, cellulose acetate butyrate, cellulose propionate butyrate, etc. The present invention is especially adapted to the processes for preparing esters containing acyl groups of more carbon atoms than acetyl as many of the non-solvents employed at the present time lessen in effectiveness as the proportion of those higher acyl groups increases.

Obviously the procedure in processes in accordance with our invention may be varied in accordance with the judgment of the individual operator. For instance the cellulose may be treated with the esterification bath for a time before the non-solvent is added, however, it is preferred that both the diluent and the esterifying ingredients be added together. Also the selection of the anhydride and catalyst to be employed and the proportions thereof will not vary the present process so as to place it outside the scope of the invention. As was pointed out previously each homogenizer exerts its own individual homogenizing effect in the esterification bath regardless of the presence of other homogenizers therein. Consequently a mixture of, a plurality of homogenizers might be employed if desired which mixture would exert approximately the cumulative effect of the individual substances.

Although ethyl ether is the preferred ether for use as an homogenizer other ethers such as normal 'butyl, iso-amyl, n-propyl, etc. may be employed as homogenizers with aliphatic hydrocarbon non-solvents in fibrous cellulose esterification processes.

In some cases the aliphatic hydrocarbon may not be refined sufficiently so that the product is rendered dark during the esterification. When this occurs the product may be bleached after 'it has been separated from the reaction mixture by suspending it in water containing a very small amount of sulfuric acid and then treating it with chlorine gas. The product formed will be almost as white as the original cotton.

The darkening of the product in a fibrous esterification process in which an aliphatic hydrocarbon is used may be readily avoided by sufficiently refining the hydrocarbon to remove any darkening impurities therefrom. This may be done by treating the hydrocarbon with fuming sulfuric acid for a time. The greater the content of sulfur trioxide in the acid, the less time will be required for the treatment to take place. For example, Stoddard solvent was purified by treating it with an equal volume of fuming sulfuric acid containing 50% sulfur trioxide for 48 hours at room temperature. If less acid or an acid containing less S03 is used a longer time of treatment is required however, the time of treatment may be reduced by using an elevated temperature.

In fibrous esterification processes in accordance with our invention various cellulosic materials such as cotton fiber tissue paper, clean cotton, surgical cotton wool or bleached sulfite wood pulp which has been carefully prepared, may be used. In processes carried out in accordance with our invention refined bagasse pulp has been found to be eminently suitable for use as the starting material. In prior processes where bagasse was employed the products have been poor in quality and gave films which were hazy, yellow in color and of low flexibility. Bagasse pulp in a process carried out in accordance with the present invention, however, gives a product which compares favorably with similar products prepared from cotton cellulose. For example 25 gms. of bagasse pulp were pulped with distilled water containing a trace of nitric acid, after which the pulp was air dried and subjected to pretreatment for 16 hrs. with a mixture of 25 c. 0. each of acetic acid and a petroleum distillate of a boiling range l50-200. Esterification was promoted by the addition of 32.5 c. 0. each of acetic and propionic anhydrides and 1 c. c. of mixed catalyst, maintaining the bath at 40 C. for 24 hrs. The product formed exhibited solubilities similar to a cellulose acetate propionate prepared from cotton cellulose. It was coated out from solution in ethylene chloride-alcohol (:5) and gave a skin of good flexibility.

We claim as our invention:

1. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath containing a lower fatty acid anhydride, a saturated hydrocarbon substantially boiling within the range -210" C. as the non-solvent, and an homogenizer selected from the group consisting of the lower fatty acids and the lower aliphatic ethers in suflicient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

2. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath containing a lower fatty acid anhydride, a saturated hydrocarbon substantially boiling within the range 150 210 C as th solvent, and a lower fatty acid in sufficient amount to assure compatibility of the ingredients of the bath, which bath will not dissolve the ester formed therein.

3. A process for preparing an organic acid ester of cellulose in fibrous form which comprises reacting upon the cellulose with an esterifying bath containing a lower fatty acid anhydride, a saturated hydrocarbon substantially boiling within the range l50-2l0 C, as th solvent, and acetic acid in sufiicient amount to assure compatibility of the ingredients of the bath, which bath Will not dissolve the ester formed therein.

4. A process for preparing cellulose acetate -propionate in fibrous form which comprises es- LOUIS M. MINSK. WILLIAM O. KENYON. HARRY LE B. GRAY.