US3720661A

US3720661A - Process for producing acetylated regenerated cellulose articles

Info

Publication number: US3720661A
Application number: US00104137A
Authority: US
Inventors: A Breton; M Tricot; A Rajon
Original assignee: Rhodiaceta SA
Current assignee: Rhodiaceta SA
Priority date: 1971-01-05
Filing date: 1971-01-05
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

A process for producing acetylated regenerated cellulose articles and such articles per se, wherein the regenerated cellulose article is acetylated first in the liquid phase and thereafter in the gaseous phase, which comprises first acetylating the regenerated cellulose article to a combined acetic acid level of from 20 to 45 percent in a liquid bath at a temperature of 80* to 135*C, such bath containing acetic anhydride and free acetic acid, in the presence of a catalytic agent having a non-acid or slightly acid reaction, the weight ratio of the acetic anhydride to the acetic anhydride plus free acetic acid being between 0.5 and 0.9, and thereafter acetylating the regenerated cellulose article to a combined acetic acid level of from 45 to 62.5 percent with acetic anhydride in the vapor phase at a temperature of 120* to 180*C.

Description

llnite States Patent [191 Breton et a1.

[ PROCESS FOR PRODUCING ACETYLATED REGENERATED CELLULOSE ARTICLES [75] Inventors: Alain Breton; Marc Tric'ot; Andre Rajon, all of Paris, France [73] Assignees: Societe Rhodiacetea; CTA Compagnie lndustrielle de Textiles Artificiels & Synthetiques, Paris, France 22 Filed: Jan.5, 1971 21 Appl.No.: 104,137

[52] U.S. C1.l ..260/227, 8/121 [51] Int. Cl. ..C08b 3/06, D06m 13/20 [58] Field of Search ..260/227; 8/121 [56] References Cited UNITED STATES PATENTS 1March 13,1973

FOREIGN PATENTS OR APPLICATIONS 20,495 9/1969 Japan ..260/227 Primary Examiner-Donald E. Czaja Assistant ExaminerRonald W. Griffin AttrneySherman and Shalloway [57] ABSTRACT A process for producing acetylated regenerated cellulose articles and such articles per se, wherein the regenerated cellulose article is acetylated first in the liquid phase and thereafter in the gaseous phase, which comprises first acetylating the regenerated cellulose article to a combined acetic acid level of from to percent in a liquid bath at a temperature of to C, such bath containing acetic anhydride and free acetic acid, in the presence of a catalytic agent having a non-acid or slightly acid reaction, the weight ratio of the acetic anhydride to the acetic anhydride plus free acetic acid being between 0.5 and 0.9, and thereafter acetylating the regenerated cellulose article to a combined acetic acid level of from 45 to 62.5 percent with acetic anhydride in the vapor phase at a temperature of 120? to C.

10 Claims, No Drawings PROCESS FOR PRODUCING ACETYLATED REGENERATED CELLULOSE ARTICLES The present invention relates to a process for the production of acetylated regenerated cellulose articles in the form of fibers, filaments, yarns, and fabrics, etc., and to such acetylated regenerated cellulose articles so produced. More particularly, the present invention relates to such a process for the acetylation of regenerated cellulose articles wherein such acetylation takes place first in the liquid phase and thereafter in the gaseous phase so as to produce an acetylated product having a high combined acetic acid level.

It has for a long time been known that cellulose textiles can be acetylated in the liquid phase utilizing a bath made up of acetic anhydride optionally mixed with acetic acid, in the presence of a catalyst, at a temperature above 100C. However, such a process is limited to the production of cellulose textiles which are acetylated to a low combined acetic acid level, i.e., lower than about 45 percent, the combined acetic acid level being the ratio per cent between the weight of the combined acetic acid and the weight of the acetylated material. In this regard, when it is desired to obtain a combined acetic acid level of greater than 45 percent, difficulties are encountered in such a procedure since the acetylated cellulose undergoes a considerable swelling and partially dissolves in the acetylation bath. Such phenomena cause the fibers or filaments of the cellulose textile to stick together and, as a result, acetylated products of little commercial value are obtained.

Various proposals have been made to eliminate the foregoing disadvantages of the heretofore proposed process for the acetylation of cellulose textiles. For example, it has been proposed to eliminate the foregoing disadvantages by incorporating in the acetylation bath various liquids which are miscible with acetic anhydride but do not dissolve the cellulose acetate, such liquids being benzene, toluene or xylene, etc. While the introduction of such liquids into the acetylation bath may eliminate the problem of dissolution of the cellulose acetate, the presence of such liquids creates further drawbacks in that the regeneration of the acetylation bath is extremely complicated due to the fact that the liquids which have been used heretofore form ternary azeotropes with the acetic acid and anhydride. Accordingly, such a procedure has not been economically commercially adopted.

it has additionally been proposed and it has been known to acetylate regenerated cellulose textile articles at a temperature of between 100 and 135C, in the presence of an alkali metal acetate, utilizing a bath containing more than 95 percent by weight of acetic acid. In such a process, the acetic anhydride content is kept constantly above 95 percent by elimination of the impurities formed during the acetylation process and through the addition of further acetic anhydride as the process proceeds. Additionally, in such process, the length of the filaments, fibers, or similar cellulose articles, is kept substantially constant during the entire acetylation. While such a process has certain advantages, the elimination of the impurities formed during the acetylation reaction is extremely difficult in practice so that a certain degree of yellowness occurs in the bath and, accordingly, in the treated regenerated cellulose fibers, filaments, or similar articles. Here again, therefore, such a process has not been adopted with satisfaction.

In addition to the foregoing, it has been previously known to acetylate regenerated cellulose textiles im- 5 pregnated with a catalyst in the gaseous phase by the use of vapors of acetic anhydride either alone or mixed with air at temperatures close to the boiling point of acetic anhydride, such temperatures being between about 120 and 160C. Such process also, however, has many difficulties associated therewith. For example, in practice, the regenerated cellulose textile article is in a compact form, for example, in the form of a layer of fibers of a certain thickness, or in the form of a rove of fibers or filaments with a high count, and as a result, the degree of acetylation which is obtained is higher on the surface than in the center of the mass of fibers or filaments. Such non-uniform acetylation is disadvantageous from a commercial standpoint.

Furthermore, the slight enthalpy of the ambient gaseous medium makes it difficult to eliminate the heat produced at the time of the acetylation reaction, which reaction is very exothermic, especially at the beginning. Because of this, local overheating and a degradation and yellowing of the acetylated material often occurs. Here again, therefore, a commercially acceptable product cannot be produced from such acetylation technique.

In addition to the foregoing processes which have been previously proposed, it has also been known to subject natural cellulose fibers to a swelling treatment with acetic acid and thereafter immerse the fibers in liquid acetic anhydride heated to a temperature of 150 to 220C for a period of about 15 to 90 minutesaSuch a process, however, is utilized in the absence of any catalyst and, therefore, such process does not allow the combined acetic acid level to exceed 30 percent. Moreover, such process requires rather'long reaction times, which are not industrially advantageous, and such process requires relatively high temperatures which often cause appreciable degradation of the cellulose fibers. Accordingly, this process, like those previously discussed, has not been industrially adopted with advantage.

Finally, the literature describes a process for the acetylation of cotton fabrics which consists of immersing such cotton fabrics in glacial acetic acid, and thereafter in a bath at room temperature containing acetic anhydride and a catalyst, and finally passing the impregnated fabrics in a heated chamber wherein the acetylation is performed with the acetic anhydride carried by the fabric. in such process, however, like many of those previously described, the degree of acetylation which can be obtained is insufficient since the temperature of the acetic anhydride bath is relatively low. In addition, because the catalyst which is used in such a process is a powerful catalyst with an acid reaction, e.g., sulfuric acid or zinc chloride, whichcatalyst would notably alter the cotton if it were desired to push acetylation further, the process can only be operated to low degrees of acetylation. Additionally, it should be noted that such degree of degradation would be even greater in the case of regenerated cellulose articles. Here again, therefore, such process has not been operated with advantage.

All of the foregoing disadvantages and difficulties of previously proposed processes for the acetylation of regenerated cellulose articles have been overcome in accordance with the present invention, wherein it is possible to produce acetylated products having a combined acetic acid level of at least 45 percent up to a level of 62.5 percent.

Such process in accordance with the present invention comprises acetylating regenerated cellulose articles either continuouslyor discontinuously, first in the liquid phase and thereafter in the gaseous phase, wherein the regenerated cellulose article is first acetylated to a combined acetic acid level of between and 45 percent in a bath of acetic anhydride and free acetic acid at a temperature of 80 to 135C, in the presence of a catalytic agent with a non-acid or slightly acid character, and thereafter acetylating the regenerated cellulose article to a combined acetic acid level of between 45 and 62.5 percent with acetic anhydride in the vapor phase at a temperature of 120 to 180C with subsequent washing and drying of the acetylated article.

Accordingly, it is a principle object of the present invention to provide a process for the acetylation of regenerated cellulose articles, in the form of fibers, filaments, yarns, fabrics, etc., and such acetylated regenerated cellulose articles so produced, wherein such process eliminates the inherent deficiencies and drawbacks of previously proposed processes.

It is a further object of the present invention to provide such a process and product wherein such process comprises acetylating a regenerated cellulose article first in the liquid phase and thereafter in the gaseous phase.

It is yet a further object of the present invention to provide such a process and product wherein a regenerated cellulose article is first acetylated in the liquid phase to a combined acetic acid level of between 20 and 45 percent in a bath of acetic anhydride and free acetic acid at a temperature of 80 to 135C, and thereafter in the gaseous phase with acetic anhydride at a temperature of 120 to 180C, to a combined acetic acid level of between 45 and 62.5 percent.

Still further objects and advantages of the novel process and product of the present invention will become more apparent from the following more detailed description thereof.

The foregoing objects and advantages of the present invention are achieved through a process for the acetylation of regenerated cellulose articles in the form of fibers, filaments, yarns, fabrics, etc., wherein the acetylation is carried out first in the liquid phase and thereafter in the gaseous phase, the initial acetylation being carried out in a liquid bath containing acetic anhydride and free acetic acid to a combined acetic acid level of between 20 and 45 percent at a bath temperature of 80 to 135C. Such initial acetylation is carried out in the presence of a catalytic agent having a nonacid or slightly acid character, with the weight ratio of acetic anhydride to acetic anhydride plus free acetic acid being between 0.5 and 0.9. Thereafter, additional acetylation is conducted to a combined acetic acid level of between 45 and 62.5 percent with acetic anhydride in the vapor phase, optionally mixed with air or another gas inert to the acetylation reaction, at a temperature of to C. Thereafter, the acetylated regenerated cellulose article is washed and dryed in a conventional manner.

in accordance with the present invention, those catalytic agents having a non-acid or slightly acid character or reaction are understood to be catalytic agents, the aqueous solution of which at 4 moles per liter possesses a pH greater than 5. In this regard, any and all such catalytic agents having such non-acid or slightly acid reaction and which have been previously utilized in the acetylation of regenerated cellulose articles can be advantageously utilized in accordance with the liquidphase initial acetylation in accordance with the present invention. Accordingly, such expression as used throughout the instant Specification is meant to embrace any and all such catalytic agents which have been heretofore conventionally utilized.

Catalysts falling within the foregoing definition include such materials as the alkali metal and alkaline earth metal salts of lower carboxylic acids, e.g., acetates, propionates, butyrates, etc., particularly alkali and alkaline earth acetates. Suitable examples include sodium acetate, potassium acetate, calcium acetate, barium acetate, sodium propionate, sodium butyrate, etc. Of these potassium acetate is particularly preferred in accordance with the present invention.

in accordance with the present invention, the catalytic agent which is utilized in the initial liquid-phase acetylation reaction can be fixed on the regenerated cellulose article before acetylation or can be incorporated into the acetylation bath itself. In the first instance, good results are obtained with amounts of the catalytic agent, e.g., potassium acetate, in the order of 40 to 60 percent by weight, for example, in relation to the weight of the regenerated cellulose.

As indicated previously, the acetylation bath in the initial acetylation reaction, is composed of a mixture of acetic anhydride, free acetic and the catalyst. Here again, it is to be noted that the catalyst may be directly incorporated in the acetylation bath or added to the bath by the article to be acetylated. With the catalyst in the acetylation bath, particularly when the catalytic agent is potassium acetate, there is a tendency for the formation in the bath of a complex product produced through the fixation of the acetic acid on the potassium acetate. This, therefore, causes the bath to actually be composed of a mixture of acetic anhydride, free acetic acid and such complex of acetic acid and potassium acetate. Similar complexes may be formed when other catalytic agents are utilized in the acetylation reaction.

The acetic anhydride (Ac O) and free acetic acid (free AcOH) are present in the acetylation bath in such amounts that the weight ratio Ac O/(Ac O free AcOH) is between 0.5 and 0.9.

When the above ratio is below 0.5, the acetic anhydride present in the acetylation bath is too diluted with acetic acid. Accordingly, the rate of acetylation is then slow and the combined acetic acid level which is desired in accordance with the present invention cannot be obtained. Accordingly, such weight ratio must be at least 0.5 in order to achieve the objects and advantages of the present invention.

When the weight ratio as described above is above 0.9, the concentration of acetic anhydride in the acetylation bath is too great and the acetylation reaction progresses too quickly, resulting in a reaction which is difficult to control. For this reason, the weight ratio of acetic anhydride to acetic anhydride plus free acetic acid should not be above 0.9. Preferably, in practice, a weight ratio of 0.6 to 0.9 produces the most advantageous results.

As indicated previously, the temperature of the acetylation bath can vary from about 80 to 135C, depending upon various factors, which factors include the composition of the bath itself and the degree of acetylation which is desired at the end of the liquid-phase reaction. The precise temperature of the acetylation bath in the liquid-phase reaction should be chosen depending upon the relative concentrations of the various elements of the bath so as to avoid any crystallization.

During the acetylation reaction, acetic acid is formed. Accordingly, to obtain a homogeneous product and to maintain constant conditions throughout, it is necessary to add acetic anhydride to the acetylation bath to continuously replace that which has been consumed during the acetylation reaction and to maintain the weight ratio as defined above. At the same time, it is necessary to continuously remove a portion of the bath from the reaction system in order to eliminate any colored reaction by-product which is formed and to recover the acetic acid contained therein.

Problems associated with the foregoing procedures can be eliminatedby working with a very low bath ratio, i.e., the ratio between the weight of the material to be acetylated and the weight of the bath, and under such conditions that the fresh bath which is added exactly compensates for the used bath which is carried off by the acetylated material. Accordingly, in a preferred embodiment of the present invention, bath ratios of the order of 1/20 to 1/60 give extremely good results.

Acetylation in the initial liquid phase is conducted, as indicated previously, to a combined acetic acid level, which does not exceed 45 percent. Thereafter, acetylation is continued in the vapor phase to the desired com bined acetic acid level. Because such second acetylation has only a supplemental character and is performed on a product which is already substantially acetylated, the reaction in the vapor phase can be controlled easily without any local overheating occurring. Accordingly, pursuant to this two-step acetylation reaction in the liquid phase first, and thereafter in the vapor phase, a product can be obtained which has a very high combined acetic acid level, i.e., up to 62.5 percent, a proportion corresponding to cellulose triacetate, and yet such product is homogeneous and has excellent textile appearance.

Prior to the acetylation in the vapor phase and after the regenerated cellulose article has been acetylated in the liquid phase, the acetylated regenerated cellulose article is treated to eliminate excess bath which is impregnated in the regenerated cellulose article. This can be done by dipping or any other conventional means. After the excess acetylation bath is removed, the acetylate regenerated cellulose article is subjected to additional acetylation with acetic anhydride in the vapor phase, at a temperature of I to 180C.

Although vaporous acetic anhydride can be utilized by itself in this second stage of the acetylation reaction, it is often preferred in accordance with the present invention to utilize a mixture of acetic anhydride and a gas such as air which is inert or relatively inert to the acetylation reaction. The use of such a mixture is preferred since such a mixture has a lower dew point making it possible to avoid condensation on the inside of the equipment utilized in the acetylation reaction and to dry the partially acetylated regenerated cellulose article when it is introduced into the gaseous acetylation medium.

After acetylation in the gaseous phase, the acetylated regenerated cellulose article is washed with water to free it of any catalyst which may be contained in it and then subjected to conventional after-treatment reactions. For example, it is possible to subject the acetylated regenerated cellulose article to a bleaching treatment and finally the article is greased and dried.

As indicated previously, through the combined liquid-phase and vapor-phase acetylation of the regenerated cellulose article, it is possible to obtain a combined acetic acid level as high as about 62.5 percent. It should be apparent that the final degree of acetylation can be controlled by varying the degree of acetylation in the liquid and vapor phases. For example, when it is desired to obtain articles which are greatly acetylated, the acetylation in the liquid phase can be conducted up to combined acetic acid levels of about 40 to 45 percent. The vapor phase acetylation can then be completed to reach the highest combined acetic acid levels, for example, up to about 62.5 percent.

On the other hand, if it is desirable to obtain an article which is less acetylated, i.e., an overall combined acetic acid level of 45 to 50 percent, acetylation in the liquid phase can be conducted to a combined acetic acid level of 20 to 30 percent, and thereafter acetylation can be completed in the vapor phase to the desired level, i.e., 45 to 50 percent. Accordingly, it can be seen that the final combined acetic acid level can be controlled by varying the degree of acetylation in the liquid and vapor phase reaction. in this regard, it should be obvious that the division of the degree of acetylation in the liquid and gaseous phases can be varied to a broad extent, depending upon the final degree of acetylation desired.

In accordance with the present invention, the regenerated cellulose article can take any conventional form. For instance, the regenerated cellulose article may comprise fibers, filaments, yarns, cables, films, fabrics, and any other products made from regenerated cellulose. Accordingly, the expression regenerated cellulose article," as employed throughout, is meant to embrace any and all such forms.

While the process of the present invention is applicable to any and all such regenerated cellulose articles, it should be noted that the process is particularly applicable to the continuous acetylation of cables of regenerated cellulose filaments, and particularly applicable to the acetylation of cables of Polynosic" filaments. In this regard, fabrics obtained through the acetylation of Polynosic filaments and fibers, according to the process of the present invention, have mechanical characteristics making them eminently suitable in the textile industry.

The term Polynosic" embraces a well known class of cellulose fibers and filaments having a high modulus of elasticity and compact fibrillary structure. Such polynosic fibers which are particularly adapted for treatment in accordance with the process of the present invention are those which have, after treatment with caustic soda in a percent concentration and at C, a tenacity in the wet state greater than 18 g per tex and an elongation in the wet state less than 8 percent under a load of 4.5 g per tex. A process for producing such polynosic filaments and such filaments per se are more clearly described in U. S. Pat. No. 3,432,589.

The process of the present invention will now be illustrated by reference to the following examples. In addition, comparative examples are presented in order to show the inability of previously proposed processes to produce a product such as produced by the process of the present invention. It should be noted, however, that the examples presented herein are presented for purposes of illustration only and are not to be deemed as limiting upon the instant invention.

Example 1 A cable of continuous Polynosic" filaments, made up of 36,000 filaments of 1.4 dtex and having a total count of 50,400 dtex is passed in a saturated solution of potassium acetate (AcOK), and thereafter dried with a countercurrent flow of hot air at 100 to 105C.

After drying, the cable has a moisture level of less than 1 percent and contains 54 percent potassium acetate.

The cable, which is impregnated with the catalyst and advances at a rate of 1 m/min, is then subjected to a first acetylation in the liquid phase by passage in a bath at 120C containing 46 percent acetic anhydride, 16 percent free acetic acid and 17.5 percent potassium acetate (catalyst added to the bath, at equilibrium). The remainder of the bath is composed essentially of acetic acid fixed to the potassium acetate.

The bath is characterized by a weight ratio as follows:

R Ac O/(Ac O free AcOl-l) 0.74

The bath ratio (ratio between the weight of the cable immersed in the bath and the weight of the bath itself) is 1/40 and the passage time of the cable through the bath is 5 minutes.

The ratio R between the weight of the acetic anhydride fed to the bath per unit of time and the weight of the regenerated cellulose which passes through the bath at the same time is 2.4. To avoid too violent a reaction and to keep the desired balance, the bath is continuously fed with a mixture of acetic anhydride and acetic acid containing 90 percent by weight of acetic anhydride.

The acetylating mixture which is fed to the bath compensates exactly for the amount of liquid which is carried off by the cable. Since a very low bath ratio is used, the bath is renewed in a relatively short time, thereby eliminating any problem with respect to regeneration of the bath.

Upon leaving the bath, immediately after the liquid phase treatment, the combined acetic acid level of the cable is 45 percent.

The cable then passes over a drying device which eliminates any excess bath carried off while spreading the cable so that it takes the form of a flat ribbon (this shape favors the vapor phase reaction). The flattened cable then passes into a chamber in which a mixture of 4.5 parts acetic anhydride and one part air (by weight) circulates countercurrent to the passage of the flattened cable at a temperature of 145C.

The air is injected into the chamber in small amounts through the outlet orifice of the flattened cable. The air acts both as a diluent for the acetic anhydride, thereby preventing condensation, and as an inert gaseous barrier preventing the escape of acetic anhydride vapors. The air also promotes the drying of the web cable coming into the chamber.

The ratio R between the weight of the gaseous acetic anhydride sent into the chamber per unit of time and the weight of the cellulose going through the chamber at the same time is 5.

The cable passes through the acetylation chamber in 10 minutes and the speed of the cable at the outlet of the acetylation chamber is 1 percent less than the initial speed at the beginning of acetylation.

The cable is thereafter washed to eliminate the potassium acetate it contains, then bleached, oiled and dried.

After acetylation in the gaseous phase, the cable has a combined acetic acid level of 53 percent and has (in relation to the same non-acetylated cable) the mechanical characteristics illustrated in Table 1.

The individual filaments making up the cable are separated from one another, have a good degree of whitness, and a very satisfactory textile appearance.

The fibers obtained from this cable can be worked easily on standard spinning equipment.

The secondary swelling figures indicated in Table l and in the following Tables 11 to IV are determined as follows:

The sample of acetylated material, previously dried, is wetted in distilled water for 30 minutes, then centrifuged at 1,350 G for 16 minutes.

The weight of the wet material P is then determined.

Then the sample of wet material is dried at C to constant weight.

The weight of the dried material P0 is determined.

The secondary swelling in percent is equal to:

Table 1 Acety- Nonlated Acetylated Cable Cable Combined AcOH level 53.5 0 Secondary swelling 15 68 Count, dtex 2.3 1.54 Tenacity, in conditioned 32 43 state, g/tex Tenacity, in wet state, gltex 24 31 Elongation in conditioned 17 14 state (36) Elongation in wet state ('56) 20 14.7 Modulus (elongation under a 0.7 2.4 load of 4.5 g/tex when wet), Tenacity at loop g/tex 4 6 Examples 2-5 Four cables of continuous Polynosic" cables, made up of 36,000 filaments of 1.4 dtex, are individually acetylated according to the process indicated in Example 1, but under different conditions with regard to the amount of catalyst and the acetylation variables in the liquid phase and vapor phase.

The conditions under which all these examples are carried out and the physical and mechanical characteristics of the articles obtained are shown in Table II.

Table 11 Polynosic" Cable Article Treated (36,000 filaments of 1.4 dtex) Example 2 3 4 5 Catalyst: potassium acetate 51 40 52 54 in relation to cellulose LIQUID PHASE ACETYLATION Time, minutes 5 2mn 2mn 30 5 Temperature, C 100 90 120 120 A0,,O content in mixture Ac,O/ 90 90 90 90 AcOH fed to bath, Ratio R (Ae Olcellulose) 2.1 l 1.75 2 Ratio R, (Ac,O/Ac,0 0.79 0.87 0.78 0.74 free AcOH) VAPOR PHASE ACETYLATION Time, minutes 5 5 10 Temperature, C 150 158 157 145 Ratio Ac,O/air 4.5 only Ac,0 4.5 Ratio R, (Ago/cellulose) 9.5 5 5 9.5 Drawing or slack -l l -1 +3 PROPERTIES OF ARTICLES OBTAINED Combined AcOH level after liquid phase, 37 24.6 42 42 after vapor phase, 50 47 53 54.5 Secondary swelling l6 16 16.5 Count,'dtex 2.4 2.3 2.4 2.3 Tenacity, g/tex conditioned state 34 39 33 33 wet state 24 28 25 Elongation conditioned state 14 l4 16 13.5 wet state 19 16 23 18.5 Modulus (elongation under 4.5 0.7 0.7 0.7 0.7 g/tex, wet state) Tenacity at loop, g/tex 5 5.5 4.4 4.4

Examples 25 clearly show that the process of the present invention can be applied within broad ranges of temperature, concentration and time and that it is possible to obtain highly acetylated regenerated cellulose articles having good physical and mechanical properties.

More particularly, with reference to Examples 3 and 4, it can be noted that the totalacetylation time is extremely short; this is due particularly to the fact that the acetylation in the gaseous phase is performed with pure acetic anhydride.

Examples 6-8 A cable of continuous filaments of non-"Polynosic regenerated cellulose composed of 10,000 filaments of 4.7 dtex and a cable of continuous Polynosic filaments composed of 36,000 filaments of 1.4 dtex are individually acetylated by the procedure indicated in Example l, but under different conditions with respect to the level of catalyst, acetylation variables in the liquid phase and vapor phase, and the degree of drawing or slack.

Additionally, Polynosic fibers of 1.4 dtex and 40 mm in length of section are acetylated in fiber form, being subjected to two distinct stages, a first acetylation in liquid phase, then a second acetylation in vapor phase.

The conditions under which all of the above examples are carried out and the physical and mechanical characteristics of the articles obtained are represented in Table 111.

Table III Article treated Non-Polynosic Cable (10,000

filaments of 4.7 dtex Polynosie Cable (36,000 filaments of 1.4 dtex) Polynosic fiber of 1.4 dtex 40 mm Example 6 7 8 Catalyst: potassium 53 54.5 55

acetate in relation to cellulose LIQUID PHASE AC ETY LATION Time, minutes 5 5 5 Temperature, "C 118 117 125 Ac,O content of Ago/AcOH 9O mixture fed to bath Ratio R (Ac,O/cellulose) 3.1 3 5.5 Ratio R, (Ac,0/Ac,0 0.84 0.63 0.86 free AcOH) VAPOR PHASE ACETYLATION Time, minutes 10 10 10 Temperature, "C 145 145 Ratio Ac,O/air 4.5 2.4 4.5 Ratio Ry (Ac,/cellulose) 9.5 5 5 Drawing or slack +3 1 0 PROPERTIES OF ARTICLES OBTAINED Combined AcOH level after liquid phase 47 31 38 after vapor phase 57 45.5 47 Secondary swelling 16 20 Count, dtex 6.8 2.1

Tenacity, gltex conditioned state 16.5 39

wet state 11.5 28

Elongation conditioned state 30 14 wet state 37 15 Modulus (elongation under 1.4

4.5 g/tex, wet state) Tenacity at loop, g/tex 5.5 4

Examples 6-8 illustrate that the process of the present invention can be applied in broad limits of temperature, concentration and time and that it is possible to obtain highly acetylated regenerated cellulose articles having very good physical and mechanical properties.

In Example 6, the article which is acetylated is composed of regular filaments of regenerated cellulose (non-Polynosic"), the degree of crystallinity of which is less than that ofPolynosic" filaments. ln Example 6, a relatively high ratio R is used in the liquid'phase. For these reasons, the filaments leaving the liquid phase reaction have too high a combined acetic acid level (47 percent) and are therefore stuck together and gelified. Example 6, therefore, shows that it is not advantageous to go beyond a level of 45 percent in the liquid phase.

in Example 7, the acetic anhydride concentration of the mixture of acetic anhydride and acetic acid which is fed to the liquid bath is low (70 percent) and the ratio R is low. This explains the relatively'low combined acetic acid levels which are obtained, i.e., 31 percent at the outlet of the liquid phase and 45.5 percent at the outlet of the vapor phase.

Examples 9-11 Two cables of continuous Polynosic filaments, composed of 36,000 filaments of 1.4 dtex, are individually acetylated by the procedure of Example 1, but under different conditions with regard to the level of catalyst and the acetylation variables in the liquid phase and the vapor phase.

Additionally, Polynosic fibers of 1.4 dtex and 40 mm in length of section yarns with a metric number of 70/2 having 920 turns of Z twist and 600 turns of S twist per meter are spun and these yarns are then woven into a fabric having a count of 22 X (yarns per cm) in warp and woof.

This fabric is subjected to a continuous acetylation according to the process of Example 1, but also under different conditions with respect to the level of catalyst and the acetylation variables.

The conditions under which all of the above examples are carried out and the physical and mechanical characteristics obtained are represented in Table IV.

PROPERTIES OF ARTICLES OBTAINED Combined AcOH level after liquid phase X1 41 42 36 at'ter vapor phase I: 55 53 49.5 Secondary swelling 11.5 15 17.5 Count, detex 2.4 2.3 Tenacity, g/tex conditioned state 32 40 wet state 28 28 Elongation conditioned state 13 17 wet state 17 18 Modulus (elongation under 4.5 0.2 1.2 gjtex, wet state) I:

enacity at loop. g/tex 5.4 8.4

Examples 9 to 11 illustrated in Table IV again show the flexibility of this process.

In Example 10, lower proportion (44 percent) of the catalyst should be noted, which is counterbalanced by the very high concentration of acetic anhydride (99 percent) of the mixture of acetic anhydride and acetic acid which is fed to the bath.

in Example 11, it is noted that the total acetylation time is extremely short, particularly because of the high acetylation temperature in the vapor phase.

Comparative Example 1 The cable of Polynosic" filaments of Example 1 is acetylated according to a conventional process for the acetylation of cotton fabrics.

The cable is first soaked for 30 minutes in pure acetic acid at a temperature of 25, then the excess is eliminated by dipping.

The cable is then immersed for 10 minutes in a mixture of 196 g of acetic anhydride and 4 g of an acid catalyst (sulfuric acid) at a temperature of 25C, this mixture having been previously heated to C for 10 minutes, then cooled.

After this treatment, the cable is dried so as to leave on the filaments 100 percent of the mixture of acetic anhydride and acid catalyst and then introduced for 5 minutes in a chamber containing acetic anhydride at a temperature of 40C.

Finally, after reaction in the vapor phase, the product is washed and dried.

Thus, a rigid, brown cable is obtained, the filaments of which are entirely stuck together and which therefore have no textile value. The combined acetic acid level of the cable amounts to only 24 percent.

Comparative Example 2 The cable of Polynosic" filaments of Example 1 is treated in the same manner asin Comparative Example 1 except that the immersion time in the mixture of acetic anhydride and catalyst is only 5 minutes instead of 10 minutes.

The cable obtained under these conditions is less colored, but its acetic level has dropped to 3 percent and there are more numerous points of sticking between adjacent filaments.

Therefore, it can be seen from Comparative Examples l and 2 that when regenerated cellulose is acetylated in the presence of an acid catalyst, a degraded product is obtained, stuck together and which therefore presents only a relatively low degree of acetylation.

Comparative Example 3 The cable of Polynosic filaments of Example 1 is acetylated according to another conventional process not employing a catalyst.

The cable is first soaked for 30 minutes in pure acetic acid at ambient temperature, dried, then immersed for 15 minutes in acetic anhydride also at ambient temperature. It is then dried again so as to leave on the filaments 200 percent acetic anhydride with respect to the filaments and introduced into a chamber containing dry acetic anhydride vapors at C.

The length of treatment is 90 minutes.

After the usual washing and drying, the treated cable has only a combined acetic acid level of 8 percent.

The filaments are brown, but they are not stuck to one another.

Comparative Example 4 The cable of Polynosic filaments of Example 1 is treated in the same way as in Comparative Example 3, except that the treatment of immersion in acetic anhydride is carried out for 15 minutes at 130C.

The cable obtained under these conditions is still more strongly colored and its acetic acid level reaches only 1 1 percent.

Comparative Examples 1 and 3 therefore show that when regenerated cellulose is acetylated in the absence of any catalyst, a colored product is obtained, the degree of acetylation of which is relatively slight.

It can be seen from the foregoing that the process of the present invention allows for the production of acetylated regenerated cellulose articles having a high combined acetic acid level as well as other advantageous characteristics, such filaments being uniform and extremely satisfactory from a commercial standpoint. Such advantages of the process of the present invention are only achieved when the acetylation of the regenerated cellulose articles is conducted first in the liquid phase and thereafter in the vapor phase, wherein the liquid phase acetylation is conducted to a combined acetic acid level of between 20 and 45 percent in an acetic anhydride-free acetic acid bath at a temperature of 80 to 135C in the presence of a catalyst having a non-acid or slightly acid reaction, while the vapor phase reaction is conducted up to a combined acetic acid level of 62.5 percent, utilizing acetic anhydride in the vapor phase at a temperature of 120 to 180C. 7

Again, it is to be noted that the acetylated regenerated cellulose articles having the foregoing characteristics and being in the form of fibers, filaments, yarns, cables, fabrics, or films are within the scope of the presentinvention.

While the present invention has been described primarily with regard to the foregoing exemplification, it should be understood that the present invention is in no way to be deemed as limited thereto, but rather must be construed as broadly as all or any equivalents thereof.

We claim: 1. A process for the production of acetylated regenerated cellulose articles having a combined acetic acid level of 45 to 62.5% which comprises 1. acetylating said regenerated cellulose article to a combined acetic acid level of from 20 to 45 percent in a liquid acetylating bath at a temperature of to C, said liquid acetylating bath containing acetic anhydride (A0 0) and free acetic acid (AcOl-l) in a weight ratio as defined by the equation Ac O/(Ac O free AcOH) of from 0.5 to 0.9, said acetylation being carried out in the presence of a catalyst having a non-acid or slightly acid reaction; and

2. thereafter acetylating the acetylated regenerated cellulose article from step one to a combined acetic acid leyel of from 45 to 62.5 percent with acetic anhydride in the vapor phase, at a temperature of from 120 to C.

2. The process of claim 1 wherein said regenerated cellulose article is in the form of fibers, filaments, yarns, fabrics, cables or films.

3. The process of claim 2 wherein said regenerated cellulose article comprises a cable of continuous filaments.

4. The process of claim 1 wherein said acetic anhydride in the vapor phase is mixed with a gas which is inert to the acetylation reaction.

5. The process of claim 4 wherein said gas which is inert to the acetylation reaction is air.

6. The process of claim 1 wherein the ratio of the weight of the article to be acetylated to the weight of the liquid acetylating bath is from 1/20 to 1/60.

7. The process of claim 1 wherein said catalyst comprises an alkaline metal or alkaline earth metal salt of a lower carboxylic acid.

8. The process of claim 7 wherein said alkali metal or alkaline earth metal salt of a lower carboxylic acid is potassium acetate.

9. The process of claim 1 wherein said acetylated regenerated cellulose article comprises a Polynosic" cellulose article.

10. The process of claim 1 wherein said regenerated cellulose article is impregnated with said catalyst prior to acetylation.

Claims

1. acetylating said regenerated cellulose article to a combined acetic acid level of from 20 to 45 percent in a liquid acetylating bath at a temperature of 80* to 135*C, said liquid acetylating bath containing acetic anhydride (Ac2O) and free acetic acid (AcOH) in a weight ratio as defined by the equation Ac2O/(Ac2O + free AcOH) of from 0.5 to 0.9, said acetylation being carried out in the presence of a catalyst having a non-acid or slightly acid reaction; and

1. A process for the production of acetylated regenerated cellulose articles having a combined acetic acid level of 45 to 62.5% which comprises

2. thereafter acetylating the acetylated regenerated cellulose article from step one to a combined acetic acid level of from 45 to 62.5 percent with acetic anhydride in the vapor phase, at a temperature of from 120* to 180*C.

9. The process of claim 1 wherein said acetylated regenerated cellulose article comprises a ''''Polynosic'''' cellulose article.