DE718070C - Process for the acetylation of cellulose while maintaining the fiber structure - Google Patents

Description

Process for the acetylation of cellulose while maintaining the fiber structure The present invention relates to the production of cellulose acetate by heterogeneous Acetylation, the cellulose acetate obtained being suspended in the reaction mixture remain.

It has previously been very difficult to make cellulose acetate of great technical quality To gain value after procedures of this kind, since the majority. the known procedures in practice lead to products whose solutions "only have a low viscosity and result in films on evaporation that are not pliable, yes_ are brittle themselves.

So far it was only possible to address these disadvantages by adding regulators to avoid the reaction mixture, its application and its recovery however, causes difficulties. In particular, it was suggested that the acetylation bath add sulphurous acid, which acts as a temperature regulator and also as a catalyst.

In the case of the method according to the present invention, however, without Addition of such regulators obtained very homogeneous products, the pliable films result. According to this process, it is possible to produce acetates, their solutions z. B. in Alko @ hol containing methylene chloride completely clear and very viscous the viscosity being higher than that obtained by known methods Cellulose acetates. According to the present invention, acetylation the cellulose while maintaining the fiber structure by treatment with the more than aof the amount by weight of one of acetic anhydride, acetic acid, a catalyst and a solution preventer carried out existing esterification mixture. as Dissolution inhibitor is a liquid that prevents cellulose acetate, to go into solution. The invention is characterized in that an acetylation mixture is used that is less than? -51110, preferably less than 2o0 / 0 of the anti-dissolving agent contains.

The most convenient amounts of the anti-solubilizer to be used vary depending on its nature and also depending on the amounts of acetic anhydride used and catalyst. When the amounts of catalyst, acetic anhydride. And acetic acid are set, it is advisable to use a lot of the dissolution inhibitor, which is just a little larger than that which is required for the forming Keep cellulose acetate in suspension in the liquid. This amount of dissolving inhibitors according to the invention is always less than 25% of the acetylation mixture and is generally below 20%; for certain products it can also be up to ' io ° / a and still further reduced.

When using the amounts of dissolution inhibitors given above it has been found that the cellulose fibers during the entire duration of Acetylierun.g seTir swell strongly and acetylate itself very regularly. From this results in the production of homogeneous products of great quality, entirely in the Contrary to what you have been doing so far when using large amounts of dissolving inhibitors could get. The fact that a small amount is used makes it possible according to the present invention, as a solution inhibitor also such substances as ether, apply; their application according to the previously known processes only for cellulose acetates without any technical value.

When using strong catalysts such. B. sulfuric acid or perchloric acid, it is advantageous to change the temperature of the reaction mass between the beginning and the end of the acetylation to a maximum of 20 °, preferably 10 to 15 ° or less, while performing rapid acetylation. This can be done advantageously by using a large amount of acetylation bath even be 30 to 40 times the weight of cellulose and even exceed it can achieve. The application of a large amount of the acetylation bath according to the present invention Invention contains a small amount of anti-solubilizer, allows the achievement a reaction mass that is liquid and does not settle when left to stand, what that Stirring facilitated. Despite this remarkable homogeneity of the reaction mass can later remove the cellulose acetate from the acetylation bath without difficulty be effected by filtering or centrifuging.

_ 'After the cellulose acetate has been removed, the acetylation bath can be used be reused in a manner known per se for further esterifications after the acetic acid formed during the acetylation is removed and the bath the suitable llenre: i of acetic anhydride and, if necessary, also a catalyst added. There is therefore no disadvantage in using a large amount of acetylation bath and using an excess of acetic anhydride, which has been found to be is, the achievement of good products favors.

Namely, it has been found that in the method according to the invention the amount of acetic anhydride far exceed three times the weight of the cellulose and Z. B. be ten times this weight or even more and even up to can be increased to almost completely exclude acetic acid. This way of working has the consequence that the viscosity of the solutions obtainable from the cellulose acetates is greatly increased, these solutions still remaining completely clear and homogeneous.

The method of the present invention can advantageously be used in a rotating device of the type described in German Patent 511; g3 Device with or without an internal stirrer and without external cooling are executed. But you can also use methods known per se, fixed, use devices equipped with stirrers or the acetylating liquid, preferably at high speed (e.g. 40 times the weight of cellulose per minute), due to the swollen cellulose mass, which itself has not been stirred will circulate.

In this case, the more or less layered cellulose mass can consist of liiters, raw cotton, cotton fibers, various types of cotton fabrics or dyed cotton fabrics. The rapid circulation of the acetylating liquid is only necessary during the ezothermic phase of the reaction and can be reduced considerably or completely omitted during the = endothermic phase. Some examples are given below to illustrate the invention. In the examples, parts are intended to mean parts by weight. -Examples,; -. I. Loo parts of cellulose (bleached cotton lint) are brought into contact with 100 parts 100% acetic acid for 5 hours. A mixture of the following composition, cooled to 0 °, is then added all at once: 85o parts of acetic anhydride! same . Soo parts by volume, 2400 - acetic acid (ioo 0/0) equals 2300 parts by volume, 700 - benzene equals 800 -, 2 - sulfuric acid (6o01,).

The mixture is stirred until one of the mass is removed Sample is soluble in methylene chloride alcohol, which takes about 24 hours to complete takes. The product obtained is filtered, washed and dried. His solution in a methylene chloride-alcohol mixture shows a very high viscosity. -.

2. 100 parts of cellulose (bleached cotton lint) are 5 hours brought into contact for a long time with 100 parts of 100% acetic acid. One then adds at once a mixture cooled to 0 ° with the following composition: 85o parts Acetic anhydride equals 800 parts by volume, 260o - acetic acid (ioo 0/0) equals 250o Parts by volume, 43o - ether equals 60o -, 2 -, sulfuric acid (6o%).

The mixture is stirred until one of the mass is removed Sample is soluble in methylene chloride.alcohol, which takes approximately 24 hours. That The product obtained in this way gives a solution which is even more viscous than that of the product Example i product obtained.

It should be noted that the amount of the dissolution inhibitor in the Acetylation bath only 20 percent by volume (17 percent by weight) in the case of the example i and 15 percent by volume (i i percent by weight) in the case of Example 2 and that the amount of acetylating bath in each case is approximately 40 times that used Amount of cellulose.

3. 100 parts of cellulose (bleached cotton sinter: s) are reduced to 125 ° Share 100% acetic acid in contact for hours. One sets then all at once a mixture cooled to -6 ° with the following composition: -85o parts Acetic acid aichydride same. 80o parts by volume, 1450 - acetic acid (100%) equal .. 1400 vglum parts, 430 - .ether equals 60o -, 2 - - sulfuric acid (6o ° / ö).

The mixture is stirred as long as one of the masses is removed Sample from which most of the acetylating liquid has been removed, Clearly soluble in methylene chloride alcohol, which takes about 40 hours, The product, after filtering, washing and drying, gives a very clear and see = viscous solutions.

4. 100 parts of cellulose (bleached linters) are brought into contact with 1250 parts of 100% acetic acid for 1/2 hours. Then you add up. once a mixture of the following composition, cooled to -6 °, to 85o parts acetic acid anhy drill equal to 800 parts by volume, - 145o - acetic acid (100 0/0) equal.

i4oo parts by volume, 43o - ether equals 60o -, io - - perchloric acid fo 0/0). -The mixture is stirred until a sample taken from the mass, as described in the example, a completely clear solution in methylene chloride alcohol results, which is the case after about 40 hours.

5. Loo parts of ceilulose (bleached linters) are made with 100 parts 100% acetic acid brought into contact for 8 hours. Then all at once you bet the following Mixture cooled to -9 °: 170o parts acetic anhydride, 1800 acetic acid (100%), 430 - ether, i o - perchloric acid (65%).

The mixture is stirred until one of the mass is removed Sample from which most of the acetylating liquid has been removed, im Methylene chloride alcohol gives a perfectly clear solution, which takes about 20 hours requires.

The product obtained gives after filtering, washing and drying very clear and very viscous solutions.

6. 100 parts of cellulose (bleached linters) are left for 8 hours with ioo parts 100% acetic acid brought into contact. One sets then all at once the following mixture cooled to -i3 °: 255o parts acetic anhydride, 950 - acetic acid (10o0 / 0), 430 - ether, To - perchloric acid (650/0). The mixture is stirred until a sample taken from the mass, from which the. biggest Part of the acetylating liquid has been removed in methylene chloride alcohol one completely clear solution gives what in about g4. Hours is reached.

The product is filtered, washed and dried. A solution the product thus obtained in a methylene chloride-alcohol mixture is more viscous as equally concentrated solutions of the products obtained according to Examples r to 5, which in turn are mostly more viscous than those obtained from known cellulose acetates Solutions.

The specific viscosity of the known cellulose acetates does not exceed the value of 0.300 to 0.35o at 25 ° in a solution of ig in z 1 of a mixture of 90% methylene chloride and 10% alcohol, while it is easy, according to the present invention Invention to obtain products which, measured under the same conditions, have specific viscosities of 0.400 and even 0.450 and more. The specific viscosity is determined by the formula expressed, where 21 and ijo mean the viscosities of the solution and the solvent, respectively.

The solutions of the triacetates obtained according to all of the above examples are perfectly clear and can be easily filtered, which is the case with products that have such a high viscosity, is particularly noteworthy. When executing the Acetylation of the cellulose according to the present invention gives a triacetate of great homogeneity, which is insoluble in the usual solvents. If If the action of the acetylation bath is prolonged, homogeneous ones are obtained Products that z. B. soluble in alcohol containing methylene chloride and extremely are viscos. The viscosity of the product decreases with longer exposure little by little, without, however, the great homogeneity that was originally obtained Triacetate denotes that is lost.

A known method is used to obtain very viscous products proposed cellulose with about 26 times the weight of a bath to acetylate, besides acetic anhydride, benzene and sulfuric acid a very contains a large amount of acetic acid. In the known method, however, the dissolution preventer becomes applied in an amount equal to about 57% of the acetylation bath. A comparison of the products obtained by the known process with the products obtained by the process Obtained by the present invention clearly reveals a superiority of the new one Cellulose acetates with regard to the transparency and the viscosity of the solutions as well as in terms of shelf life and solubility.

Claims (1)

PATENT CLAIM: Process for the acetylation of cellulose while maintaining the fiber structure by treatment with more than 2 times the amount by weight of an esterification mixture consisting of acetic anhydride, acetic acid, a catalyst and a solubilizer, characterized in that an acetylation mixture is used which is less than 250/0, preferably contains less than 20% of the anti-solubilizer.