US2218029A

US2218029A - Process of producing articles from cellulose acetate

Info

Publication number: US2218029A
Application number: US184968A
Authority: US
Inventors: Hubert Emil; Hofmann Rudolf; Pabst Heinrch
Original assignee: IG Farbenindustrie AG
Current assignee: IG Farbenindustrie AG
Priority date: 1937-01-19
Filing date: 1938-01-14
Publication date: 1940-10-15
Anticipated expiration: 1957-10-15
Also published as: NL46526C; GB509702A

Description

- said proposals, for instance, their strength and Patented Oct. 15, 1940 UNITED STATES.

os'a'rwms mom raocsss or raonucm caummsa scsrs'ra Emil Hubert, Dessau-Ziebigk, and Bureau 1101- mann and Heinrich Pabst, Donnagen, Germany, assignors to I. G. Farbenindustrle Aktiengesellschsit, many Frankfort-on-the-Main, Gel- No Drawing. Application January 14, 1936, Se-

rial No. 184,968. 193':

This invention relates to a process of -producing shaped articles from cellulose acetate and more especially from cellulose acetate which is soluble in chloroform. It is known to produce shaped articles for instance, fibres or threads,

from acetone soluble cellulose acetate by spinning a solution 'of hydrolized and thereafter precipitated cellulose acetate according to either the dry or the wet spinning method. It has also been tried to produce in a similar way shaped articles from cellulose acetate which has not been hydrolized to the acetone soluble stage, butwhich is still soluble in chloroform like the primary acetate obtained in the customary acetylation processes. However, the hitherto made proposals of this kind met with great dimculties. Clogging of the filters and nozzles of the spinning machines and breakage of the filaments very frequently occurred, thereby making the continuous operation of the spinning process impossible. Moreover, the mechanical prop erties of the filaments obtained according tothe extensibility, and also their luster and softness did not come up to the present high practical standards.

It is an object of our inventiton to furnish a method of producing shaped articles from chloroform-soluble cellulose acetate which will not give rise to the above-mentioned'difficulties anddisadvantages and which will yield high quality products which will stand any competition in the market. In the following our invention will be described more particularly as applied to the manufacture of fibres and filaments from chloroform-soluble cellulose acetate. However, it will be easily understood that the invention may also be applied to the production of other shaped articles like, for instance, bands, films, foils, artificial horse hair and so on. The process according to our invention may. be shortly summarized as follows:

A crude solution, of cellulose acetate as primarily obtained by acetylating cellulose, after rendering the acetylation catalyst inefl'ective and establishing the desired cellulose acetate content, is heated to higher temperatures and is thereupon spun into an aqueous inorganic salt solution of lower temperature. Further particulars of our invention will be apparent from the following more detailed description thereof.

It is of particular significance for the usefulness of our new process that it allows spinning crude cellulose acetate solutions, 1. e., the solutions as they are primarily obtained in the cus- January 19, 'lClaims. '(ci. rs-so tomary acetylation processes 'of' cellulose; It is only necessary to-render the acetylation catalyst (which in mostcases is sulfuric acid) ineffective; so that during the further stages of manufacture the catalyst has no injurious action on the cellulose'acetate' solution or on the finished products. It will be understood that in this respect those -crude cellulose acetate solutions are especially suitable for use in the present process which have been prepared in the presence of 10 small amounts, of catalyst acid, as, for instance, in the acetylation process using methylene chloride in the acetylation mixture as described in the U. 8.- Patent No. 2,126,190. 1

It is not absolutely necessary that the acetic acid content of the cellulose acetate corresponds to the theoretical value of primary cellulose acetate (cellulose trlacetate), i. e., 62.5%. On the contrary, the solutions are more easily to be spun if a slight hydrolysis has been performed 20. which, however, should not go so far as to change the solubility of the cellulose acetate; the latter should still be soluble in chloroform and substantially insoluble in acetone. This means that the acetic acidcontent ,of the cellulose acetate 2 may vary between about 59% and the theoretical value; preferably the acetic acid content is between about 60 and 61.5%.

When the crude solutions have been hydrolized the acetylation catalyst is made ineffective by neutralization which may be performed with any suitable agent. In order to avoid as much as possible precipitations taking place in the spinning solution which might clog the filters and nozzles and give rise to rupture of the filaments, 86 it has proved to be advantageous to use such neutralizing agents which form with the catalyst acid compounds which can not be removed from the cellulose acetate solution by filtration since they are either so well soluble therein as not to 40 form precipitates at all, or are forming colloidal precipitates which pass all filtration equipments without disturbance. Such neutralizing agents are, for instance, on the one hand, aliphatic bases or the salts thereof with weak acids, like 45 propylamine, isobutylamine, diisobutylamine, triethanolamine, and on the other hand, bariumhydroxide or the salts thereof with weak acids, like, for instance, barium acetate.

Thereupon the crude cellulose acetate solution 50 is brought to a suitable cellulose acetate content. It has been found that our process is working especially well if the cellulose acetate concentration of the spinning solution is between about 12 and 16%. Furthermore, a small content of as methylene chloride and water (from about 2 to 6%) in the spinning solution has a beneficial actionon the spinning process.

As usual, for obtaining special effects other substances like filling agents, softening agents, dulling agents, dyestuffs and so on may be added to the spinning solution.

Thereupon the cellulose acetate spinning solution is heated to a temperature which is higher than the temperature of the precipitating bath. How much the spinning solution should be heated in order to establish the most favorable conditions for spinning depends somewhat on the concentration or the viscosity res ectively of the spinning solution. Ifspinning solutions of higher concentration or higher viscosity are used, they are preferably warmed to 70 to 80 or even 90 C., whereas, if working with spinning solutions of lower concentration or viscosity it may be sufficient to heat them to about 50 to 60 C.

The heated spinning solution is then extruded, for instance through one of the customary spinning nozzles into an aqueous inorganic salt solution which in comparison with the spinning solution is of lower temperature. Many kinds of inorganic salt solutions may be employed for this purpose which partly have been proposed already in literature, for instance, solutions of sodium acetate or calcium chloride. As especially valuable we have found, however, aqueous solutions of ammonium salts. The concentration of these precipitating solutions may vary within wide limits, for instance, between about 10 to 30%; their temperature may go up to about 30 to 40 C.

The precipitating liquid is preferably caused to act on the precipitated filaments in countercurrent, the quantity and the velocity thereof being so chosen that the acetic acid content of the precipitating liquid increases up to to 30%. On observing these conditions, there are obtained filaments of very good mechanical and textile properties, for instance, strength, extensibility, luster and softness. Moreover, the acetic acid can bemore easily recovered from the solutions which themselves are of relatively high acetic acid concentration.

By the concurrent action of the previously described features of our invention it is now possible to manufacture shaped articles from crude cellulose acetate solutions of high quality in a simple and economical manner. For instance, fi amentscan be produced having a titre of from 3.5 to 4.5 den., a breaking strength of 1.3 to 1.7 gr. per demand an extensibility of to 40%. An outstanding problem of cellulose acetate manufacture has thereby found its solution.

Example 1 100 parts of cellulose which have been bleached and pretreated in the usual manner are acetylated with a mixture of 2'75 parts acetic acid anhydride, 400 parts methylene chloride and 1.3 parts sulfuric acid (specific gravity 1.84). When the reaction is complete the excess anhydride is destroyed by adding 50 parts of 50% aqueous acetic acid. The solution is then hydrolized, by heating to 50 to 60 C. for 2 to 6 hours to an acetic acid content of the cellulose acetate of 60 to 61%. After neutralizing the catalyst, the excess methylene chloride is distilled off, the solution brought to a content of 14% acetyl cellulose, 2% methylene chloride, 3% water and 81% acetic acid, filtrated and deaerated. On its way to the spinning nozzle the solution is heated in a double-walled pipe by means of hot water (of 70 to 80 C.) and spun into a 20% aqueous chloride solution of C. which is acting in countercurrent on the precipitated cellulose acetate. The rate of flow of the precipitating solution is so chosen that its acetic acid content near the spinning nozzle increases up to 17 to 20%.

Example 2 solution is caused to act on the filaments of cellulose acetate in such a manner that its acetic acid content near the spinning nozzle increases up to 20 to 25%.

Example 3 A filtrated and deaerated spinning solution prepared as described in Example 1 and having a content of 13% acetyl cellulose, 2% methylene chloride, 3% water and 82% acetic acid is heated on its way to the spinning nozzle to 55 to 65 C. and spun into a bath of 15% aqueous ammonium chloride and having a temperature of 15 C., the said bath acting in countercurrent on the precipitated filaments of cellulose acetate.

Example 4 A spinning solution as described in Example 3 is heated before entering the spinning nozzle to '70 to 80 C. and spun in countercurrent into a 20% aqueous common salt solution of C.

Example 5 A cellulose acetate spinning solution as described in Example 1 is heated to 70 to 80 C. and is thereupon spun through a spinning nozzle into a 30% aqueous ammonium acetate solution oi C.

Instead of into an ammonium acetate solution, the cellulose acetate solution may also be spun with a similar effect into a 20% aqueous sodium sulfate solution.

We claim:

1. Process of producing shaped articles from cellulose acetate soluble in chloroform which comprises heating a crude acetic acid solution as primarily obtained by acetylating cellulose to a temperature above 50 C. and spinning it into an aqueous inorganic salt solution of a temperature below C.-

2. Process of producing shaped articles from cellulose acetate soluble in chloroform which comprises hydrolizing a crude acetic acid solution as primarily obtained by acetylating cellulose until an acetic acid content of not less than 59% is reached, heating said solution to a temperature above 50 C., and spinning it into an aqueous inorganic salt solution of a temperature below 40 C.

3. Process of producing shaped articles from cellulose acetate having an acetic acid content of from 59 to 62.5% which comprises rendering the acetylation catalyst of the crude solution as primarily obtained by acetylating cellulose ineffective, bringing the solution to an acetate content of about 12-16%, heating it to a temperature above 50 C., and spinning it into an aqueous inorganic salt solution of a temperature below 40 C.

4. Process of producing shaped articles from cellulose acetate soluble in chloroform which comprises rendering ineffective the acetylation catalyst in the crude solution of cellulose acetate as primarily obtained by :acetylating cellulose, bringing the solution to an acetate content of about 12-16%, heating it to a temperature above 50 C-., said solution containing of from 2-6% of Water and methylene chloride, and spinning it into an aqueous inorganic salt solution of a temperature below about 40 C.

5. Process of producing shaped articles from cellulose acetate having an acetic acid content of from 59-62.5% which comprises rendering ineffective the acetylation catalyst contained in the crude acetic acid solution as primarily obtained by acetylating cellulose, bringing the solution to an acetate content of about 12-16%, heating it to a temperature above 50 0., said solution containing of from 2-6% of water and methylene chloride, spinning it into an aqueous inorganic salt solution of a temperature below about 40 C., and leading the said inorganic salt solution in a coun'tercurrent to the flow of the precipitated cellulose acetate.

6. Process of producingshaped articles from cellulose acetate having an acetic acid content of from 5962.5% which comprises rendering inefiective the acetylation catalyst contained in the crude acetic acid solution as primarily obtained by acetylating cellulose, bringing the solution to an acetate content of about 12-16%, heating it to a temperature above 50 C., said solution containing of from 2-6% of water and methylene chloride, and spinning it into an aqueous. solution of an ammonium salt of a temperature below about 40 C., and leading the said ammonium salt solution in countercurrent to the flow of the precipitated cellulose acetate.

7. Process of producing shaped articles from cellulose acetate having an acetic acid content of from 59-62.5% which comprises rendering inefiective the acetylation catalyst contained inthe crude acetic acid solution as primarily obtained by acetylating cellulose, bringing the. solution to an acetate content of about l2l6%, heating it to a temperature above 50 C., said solution containing of from 2-6% of water and methylene chloride, and spinning it into an aqueous solution of an ammonium salt of a temperature below about 40 C., and leading the said ammonium salt solution in countercurrent to the flow of the precipitated cellulose acetate in such a manner that the acetic acid content thereof increases up to from 15-30%.

EMIL HUBERT.

RUDOLF HOFMANN. HEINRICH PABST.