US3073669A - Method for producing shaped articles from polymers and copolymers of acrylonitrile - Google Patents

Description

States 3,073,669 METHOD FOR PRODUCING SHAPED ARTICLES FROM POLYMERS AND COPOLYMERS F AC- RYLONITRILE This invention relates to a method of producing filaments or fibers from polymers and copolymers of acrylonitrile. More particularly, this invention relates to an improved method of coagulating acrylonitrile polymer from its solution in 69% or more nitric acid.

Various methods of producing shaped articles and especially fibers from polyacrylonitrile and from copolymers or interpolymers of a major proportion of acrylomtrile and a minor proportion of another monomer or monomers heretofore have been suggested. Among these methods, a review will be given with respect to several methods for the preparation of fibers wherein polyacrylomtrile be dissolved in an inorganic solvent and the resulting solution be subjected to wet spinning.

In U.S. Patent No. 2,140,921 a concentrated aqueous solution containing such inorganic metal salts as. zinc chloride, sodium thiocyanate, calcium thiocyanate, lithium bromide and aluminium perchlorate are proposed as solvents for polyacrylonitrile. Rein: Agnew. Chem. 60, 159 (1948), Keln: J. Prakt. and Kanbara: Japanese Patent No. 147,451, disclose that an inorganic acid solution is usable as a solvent for polyacrylonitrile. As pointed out by researchers of E. I. du Pont de Nemours & Co., however, these inorganic solvents commonly have serious drawbacks and therefore they arenot so suitable for the production of shaped articles from polyacrylonitrile. Recently these inorganic solvents have been improved to some extent, for instance, in Cresswell U.S. Patent No. 2,558,730 which relates to thiocyanate-containing solvents, Stanton U.S. Patent Nos. 2,648,592-3 which relate to chloride-containing solvents, and Fujisaki et a1. Japanese patent publication Nos. 984- 5/1957, 1,443/1957, 9,516/1957, 10,866/1957 and 965/ 1958 which relate to nitric acid-containing solvents. Thus the production of polyacrylonitrile fibers wherein aqueous solutions of inorganic acids and the salts thereof are used as a solvent for polyacrylonitrile is now rapidly progressing.

In the case of using nitric acid as a solvent forpolyacrylonitrile, it should be noted also that all of the defects accompanying the use of aforesaid inorganic solvents are not completely removed. One such defect is the high viscosity of the spinning solution. However, the viscosity is far lower than that with other inorganic compounds, such as ordinary inorganic salt concentrated aqueous solution solvent or phosphoric acid containing spinning solution, but is highly viscous compared with organic solvent spinning solutions.

Even when nitric acid is employed as the solvent there is some difficulty in the treatment of the solution due to its relatively high viscosity. It is difficult to maintain the spinning solution at high temperatures or to heat the coagulating bath to lower the viscosity of the spinning solution during extrusion since such heating tends to hydrolyze the nitrile group in the polyacrylonitrile molecular chain. As the results of our extensive studies on spinning processes employing inorganic and organic solvents, it has now been found that the less a difierence between the temperatures of a spinning solution and a coagulating bat the better $59 h PQ of t n Chem. 160, 281 (1942),-

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parency of coagulated filaments and transparency as well as luster of fibers after stretching is obtained. Results serving these purposes were obtained when a difference between the temperatures of the aforesaid spinning solution and coagulation bath was less than 5 C.

In comparison with a dry spinning process or the extrusion of a spinning solution containing an organic compound e.g. dimethyl formamide as a solvent into a coagulating bath containing glycerine, another defect accompanying the use of a concentrated solution of nitric acid is that during a period of coagulation it is hardly possible to subject to a tension the extruded filaments in a fluid state. As observed in a dry spinning process, if it is possible to subject to a tension the extruded filaments in a fluid state, it will be of great advantage because that desired fineness of fibers can be obtained by applying a suitable degree of tension and that the nozzle having holes of relatively greater diameter can be used.

As will be known by those skilled in the art, the use of a nozzle having holes of a greater diameter is advantageous in the operation of extrusion. For instance, when the aforesaid'organic compound is used as a solvent for polyacrylonitrile, the nozzle having holes of diameter of 0.22 mm. can be used inorder to obtain fibers having fineness of three deniers. On the other hand, as seen in Cresswell U.S. Patent Nos. 2,648,592-3 which deal with an inorganic solvent containing thiocyanates, the nozzle having holes of a diameter of about 0.05 mm. should be employed in the extrusion of a spinning solution consisting of the inorganic -solvent.j Such disadvantage originally results from the fact that there is not any possibility to provide a tension to extruded'filaments in a fluid state.

It is necessary to maintain a nitric acid concentration of from 47% to 50% in the coagulation bath to elongate the coagulating thread-like material in the coagula= tion process in a fluidizing manner inorder to improve various properties of the fiber, which is one of the objects of the present invention.

While the present invention will, for convenience, be described in connection with fiber, shaped articles produced by thepresent invention may include filaments (monoand multifilaments), foils, ribbons, films, sheets, etc. Since many diiferent embodiments of the invention may be made by those skilled in the art without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves except as set forth in the description and claims which follow.

An object of the present invention is to provide an improved method for coagulation of solutions of acrylonitrile polymerization products, said method suiting for the production of fibers having good mechanical properties, e.g. toughness, resilience, and excellent loop elongation in addition to fine appearance. i

Another object of this invention is to provide a method of producing non-brittle, tough shaped articles from acrylonitrile polymerization products.

Still another object of the present invention is to provide the production of fibers having excellent loop elongation. T

Further object of the present invention is 'to provide the production of polyacrylic synthetic fibers having fine lustre and good resilience.

Other objects, features, capabilities and advantages which are comprehended by the invention will be appar: ent from the description and claims which follow.

According to the present invention, an acrylonitrile polymerization product is dissolved in 69% -or more nitric acid, the resulting solution is extruded. into the first liquid coagulating bath having approximately same temperature as that of said solution and having 47% to 50 .Ilitrig, acid, h Q1 dedv mes is t etchedto desired times its original length in a fluid state while passing through said bath, then the extruded and stretched mass is passed through the second liquid coagulating bath comprising mainly water thereby to form a shaped tough gel of said polymerization product which can be molecularly oriented by wet stretching, and the thus shaped gel is dried.

Acrylonitrile polymerization products used herein as a starting material include polymers and copolymers comprising about 85% or more than acrylonitrile and the mixtures thereof. These copolymers include acrylonitrile copolymerization products of acrylonitrile with a monomer being copolymerizable therewith. Illustrative examples of monomers which may be copolymerized with acrylonitrile are compounds containing a single CH =C group, for instance the vinyl esters and especially the vinyl esters of saturated aliphatic monocarboxylic acid, e.g., vinyl acetate, vinyl propionate, vinyl butyrate, etc.; acrylic and alkacrylic acids (e.g., methacrylic, ethacrylic, etc.) and esters and amides of such acids (e.g., methyl, ethyl, propyl, butyl, etc., acrylates and methacrylates, acrylamide, methacrylamide, N-methyl, -ethyl, -propyl, -butyl, etc., acrylamides and methacrylamides, etc.); similar compounds of saturated aliphatic dicarboxylic acids (e.g. itaconic, maleic, etc.) and the anhydrides of such acids; methacrylonitrile, ethacrylonitrile and other hydrocarbon-substituted acrylonitriles; numerous other organic compounds which are copolymerizable with acrylonitrile. A suitable method of polymerizing the monomeric acrylonitrile or mixture of monomers is a redox polymerization or a'sus'pension polymerization in a heterogeneous phase or an emulsion polymerization using a dispersing agent. Other polymerization methods, however, also may be employed. The acrylonitrile polymerization product may be of any suitable weight average molecular weight, and ordinarily will be within the range of 30,000 to 150,000 or higher.

In the practice of this invention into effect the acrylonitrile polymerization product is then dissolved in a nitric acid from which the acrylonitrile polymerization product is slowly coagulated when the solution is brought into contact (e.g. immediately after extrusion) with a coagulating solution fully described hereinafter.

It will be understood by those skilled in the art that the solution of the acrylonitrile polymerization product in nitric acid should be of such a concentration that a workable viscosity is obtained. The concentration of the acrylonitrile polymerization product will depend, for example, upon the solvent composition and extrusion apparatus employed, the type of shaped article to be formed and the weight average molecular weight of the acryacrylonitrile polymerization product, which usually is within the range of 30,000 to 150,000. The concentration of acrylonitrile polymers in spinning solution may range, for example, from 5% to 20% and/or more by weight. However, improved fibers are obtainedby employing a spinning solution having a viscosity of at least 1000 poises. Also it is noted that this solution when extruded into a coagulating bath should be maintained at the temperature of from C. to 10 C.'or lower.

In the present invention the solution of the acrylonitrile polymerization product is extruded into a coagulating bath and then stretched in a fluid state while passing through said bath. The coagulating bath used herein should have a concentration of 47% to 50% nitric acid. Highly concentrated nitric acid, however, has not previously been employed for the coagulationbath in known spinning processes. An industrial advantage, of highly concentrated nitric acid as the coagulation bath is the reduced expense of recovery and purification for cyclic use. The mass which'has beenstretched inv a fluid state i then passed through the second liquid coagulating'bath in which said mass is completely-coagulated. It is not so preferred to have much time for transferring said mass from the first coagulating bath to the second one.

With respect to nitric acid used as solvent, the solvent power for polyacrylonitrile is as follows:

solved. Polyacrylonitrile is well swollen 5 C. Polyacrylonitrile is dissolved Considerably low temperature.

52.47 54% 6: higher The above data show that the critical concentration of an aqueous nitric acid solution for polyacrylonitrile is approximately 53% In order for stretching advantageously the extruded mass five times or more in a fluid state in the first liquid coagulating bath, however, it is preferred to have the nitric acid concentration of the coagulating bath 47% or higher. Thus, the extruded mass may be stretched at a desired ratio in the first liquid coagulating bath having the suitable concentration of nitric acid.

Then the stretched mass is passed into the second liquid coagulating bath containing less than 35% of nitric acid or nitric acid salt or the mixture thereof, and it is completely coagulated in said bath and then washed with water.

It is necessary that the concentration of the second liq'uid coagulating bath is lower than that of the first liquid coagulating bath.

To coagulate the fiber conveniently in the gelled state, the temperature of the second coagulating bath should be as low as possible, but within the range of from +40 to 5 C. The temperature of the second coagulating bath, however, does not affect the properties of the finished product. As will be understood from the above description, the thread in the first liquid coagulating bath consisting of an aqueous solution having a relatively higher concentration of nitric acid is not in perfectly coagulated form and therefore it can be stretched by a little force like a fluid. That is to say, it is treated under such a state that binding force between molecular chains of polymer is remarkably weakened. This force may cause shear within the fluid, and very desirable molecular orientation can be promoted at a low temperature. In forming a perfect gel structure in the second coagulating bath, the characteristic mentioned above may promote formation of a gel structure which is desirable for subsequent heat stretching. Furthermore when a stretch, that is, shear applied to the fluid in the first coagulating bath, is very high, the swollen mass in which molecular chains are oriented tends to be converted into more compact form. Such tendency is more effectively developed when the higher concentration of polymer is employed. By our discovery, therefore, if a very high degree of shear is applied in the first coagulating bath, it is possible to transfer the extruded and stretched mass directly from the first coagulating bath to a water-washing bath without passing through the second coagulating bath.

For the gelled thread, passed through the first coagulating bath and second coagulating bath and the washing "bath, the heat stretchability is affected by the stretching ratio of the tension in a fluid state in the first coagulating bath. That is to say, the more increasing the stretch ratio in the first coagulating bath, the more decreasing the heat stretching ratio.

Moreover, a factor of shear of the spinning solution on the nozzle is accompanied with this relation, its efiect, however is evident by the table followed which is a part of our experimental results.

TABLE I.-THE RELATION BETWEEN THE STRETCHING RATIO IN THE FIRST OOAGULATING BATH AND THE HEAT STRETCH RATIO Stretching ratio in the 1st coag. bath (times) Rate of shear bath 2 5 l 15 20 25 30 50 m./ min.) 1

Heat stretching ratio 1 Rate of shear is indicated in linear velocity of spinning solution at the time of leaving the nozzle.

As mentioned above, the application of stretching to an extruded mass having fluid properties in the first coagulating bath is highly suitable for orientation of polymer molecules, and the behaviors of these polymer chains are similar to those in melt spinning. In a conventional method which comprises extruding a solution of the polyacrylonitrile in a concentrated aqueous solution of nitric acid into a coagulating bath and coagulating the extruded mass while passing through said bath, the fluid is molec ularly oriented to some extent due to nozzle shear, but it tends to shrink immediately after the extrusion from the nozzle. In this case, therefore, it is impossible to stretch the extruded mass one or more times to its original length. Such shrinkage which usualy extends over 10 to 70% or higher and which happens in a coagulating bath has entanglement of molecular chains promoted. The coagulated filament which has a coagulated gel structure produced under the above said situations will be harmed by great constrained forces against individual molecular chains or micell groups when said filament is subject to heat stretching in the subsequent process. As its result, fibers obtained would be brittle. Consequently speaking, there is a remarkable difference between a polyacrylic fiber of the present invention and that of a conventional method in the point of brittleness. In the present invention, brittleness will be expressed in ball mill value. When a certain amount of fibers are ground in a particular ball mill for 2 hrs. and then the finely powdered fibers are weighed, the ball mill value is calculated according to the following manner:

=ball mill value (percent) Now acrylonitrile polymer is dissolved in an aqueous 70% nitric acid solution to prepare a spinning solution. In accordance with a conventional method, the spinning solution is extruded into an aqueous 30% nitric acid solution to prepare coagulated filaments. After" washing with water, the filament is heat-stretched to seven times its original length. The thus produced mass has a ball mill value of 67%. According to the present invention, the above spinning solution is extruded into the first coagulating bath being an aqueous 49% nitric acid solution and the extruded mass is stretched thirteen times its original length.

After coagulating in the second coagulating bath in an aqueous 28% nitric acid solution, the extruded and stretched mass is further heat-stretched seven times its original length. The thus produced mass has a ball mill value of 5% In a conventional process the above spun fiber is unable to be heat-stretched more than eight times its original length. In the present invention, however, it is noted that the spun fiber can be heat-stretched up to fourteen times its original length, and higher order of stretching, the treated fiber can obtain several features of desirable mechanical properties such as lustre of the fiber, strength, etc. Further-more loop elongation of the fiber may be improved corresponding to the decrease of brittleness.

As stated hereinabove, one of the characteristics of the invention resides in the fact that a highly viscous spinning solution can be readily worked. Such a fact will permit to have the more higher concentration of polyacrylonitrile in a spinning solution, whereby the productivity of fiber per unit volume of solvent is developed. At the same time the thus produced fiber may be provided with good properties which are beyond our expectation. That is to say, the fibrillation of the fiber is scarcely observed and the resilience of the fiber is remarkably improved.

Heretofore it was found that there was a limitation in the molecular weight of polyacrylonitrile employed when nitric acid was used as the solvent. In accordance with the present invention, however, an acrylonitrile polymerization product having a molecular weight higher than that of any acrylonitrile polymer heretofore used may be used for preparing a spinning solution having an ordinary concentration of said polymerization product. In the present invention, for instance, polyacrylonitrile having a molecular weight of 100,000 or more than can be used. This fact also serves to improve the strength of fiber.

Furthermore, the fiber produced by the present invention can be easily relaxed by heattreatment after drying said fiber. For example, polyacrylonitrile fiber can be relaxed by dry heat treatment and show a loop elongation of over ten percent. By wet heat treatment, this fiber can be relaxed at the lower temperature, e.g. C., than the relaxing temperature of any conventional po-lyacrylic fiber.

The coagulating bath used in the present invention should be at a temperature of less than 20 C. and preferably less than 10 C. But it is unobjectionable that a water-washing bath is warm water having a temperature of less than 70 C.

Additionally speaking, it is not only unobjectionable to carry out stretching at a low ratio in a second coagulat ing bath, but it is rather preferred. If necessary, however, also it is allowed to shrink to some extent in the said bath, as occasionally observed in a conventional spinning process.

The following examples, will serve to illustrate this invention further, without however limiting the same. All molecular weights of acrylonitrile polymerization products indicated herein are calculated from the intrinsic viscosity of dilute solutions of said products in dimethyl 'formamide. In order to attain the object of the present invention to improve the fiber as indicated previously, it is indispensable that nitric acid having a concentre-tion above 69% be employed as solvent to prepare spinning solution having a viscosity of more than 1,000 poises and the spinning solution be extruded into a coagulation bath having a nitric acid concentration of from 47% to 50%. It is impossible to separate the use of highly concentrated nitric acid as solvent, the use of a highly viscous spinning solution and the use of from 47 to 50% nitric acid for the coagulation bath. In the spinning process, wherein the spinning solution is comprised of nitric acid as solvent, in which spinning solution is extruded into diluted aqueous nitric acid solution, the concentration zone (of the coagulation bath) for the nitric acid which enables spinning decreases with an increase in the concentration of solvent, since the concentration of raw nitric acid in the coagulation bath varies inversely with the concentration of nitric acid in the spinning solution. The primary factor which dominates the phenomenon of physical variation in the coagulation step is diffusion of solvent in the coagulation bath. The same effect as obtained by this invention cannot be obtained by materially lowering the nitric acid concentration in the spinning solution and increasing the nitric acid solution concentration in the coagulation bath since 7 the viscosity of the spinning solution will be too low. Only when the stated relationship between the concentration of nitric acid as solvent in the spinning solution, the concentration of nitric acid in the coagulation bath and the viscosity of the spinning solution is satisfied, will the advantage of the instant invention result.

Example 1 Polyacrylonitrile having a molecular weight of 92,000 was dissolved into 70% nitric acid aqueous solution at 3 C. for 3 hours to have a concentration of 18%. The resulting spinning solution was extruded into 48% nitric acid aqueous solution at C., and the extruded filament was stretched to 24 times its original length while coagulation. Immediately thereafter, the filament was fed to an aqueous coagulation bath and further stretched twice. The filament was passed into a water-washing bath and washed with water. Then the washed filament was subjected to heat stretching to 5 times its original length in superheated steam (270 C.) The produced fiber had a strength of 5.8 gr./d., a ball mill value of 3% and a loop elongation of 7.3%.

For comparison, the spinning solution used in the above example was spun in accordance with a previously known method. That is to say, the spinning solution was extruded into 34% nitric acid aqueous solution. The extruded filament was stretched twice its original length in the coagulating solution. After washing with water, the coagulated filament was subjected to heat stretching to 5 times its original length thereby to obtain fiber having a strength of 3.8 gr./d., a ball mill value of 54% and a loop elongation of 2.8%.

Example 2 Polyacrylonitrile having a molecular weight of 74,000 was dissolved into 70% nitric acid aqueous solution at C. to have a concentration of 18%. The spinning solution resulted was extruded into 50% nitric acid aqueous solution at -7 C., and the extruded filament was stretched to 90 times its original length while coagulation. Thereafter, the filament was passed into 25% nitric acid aqueous solution to form a completely coagulated filament and then it was washed with water. Then the washed filament was stretched to 3 times its original length by heating in hot water at 100 C. The fiber thus produced had a strength of 4.2 gr./d., a ball mill value of 5%.

In accordance with a previously known method, the spinning solution used in the above example was extruded into 30% nitric acid aqueous solution and it was coagulated while shrinking to the order of 5%. After heat stretching, the produced fiber had a strength of 3.7 gr./d., a ball mill value of 50% and a loop elongation of 2.4%.

Furthermore, the spinning solution could be spun into film by extruding it in the coagulating bath consisting of 49% nitric acid aqueous solution cooled to 0 C. and in the coagulating process the film in gelled state was stretched times to improve the properties of the finished product. The film which was in the form of gel was very thin comparing that produced by published method, and clear, and had a marked toughness and resilience.

Example 3 Polyacrylonitrile having molecular weight of 74,000 was dissolved into 70% nitric acid aqueous solution at 5 C. to have a polymer concentration of 30 gr. per 100 ml. and thus the spinning solution was prepared. The nitric acid used herein was purified prior to its use to contain 0'.0002% of nitrous acid. The spinning solution prepared above showed a viscosity of 8,000 poiscs at 0 C.

The spinning solution was extruded into 48% nitric acid aqueous solution at 0 C., and the extruded filament was stretched 24 times its original length in the coagulating solution. The filament was fed to an aqueous coagulation bath wherein it was further stretched three times, was passed into water-washing bath and it was washed with water until it was free from nitric acid. Then the filament Was stretched to 5 times its original length in 300 C.--superheated steam thereby to obtain fiber having a strength of 5.2 gr./d., a ball mill value of 1%, and a loop elongation of 7.4%.

In the above experiment, the spinning conditions were same as in Example 1, excepting that the spinning solution having a very high concentration of acrylonitrile polymer was used. The result of this example, however, showed an increased strength and an improved ball mill value, as compared with those of Example 1.

Example 4 Polyacrylonitrile having a molecular weight of 120,000 was dissolved in nitric acid aqueous solution to have a polymer concentration of 8 gr./ 100 ml. and a solution having a viscosity of 5,000 poises was obtained. The used nitric acid was purified prior to its use to contain 0.0004% of nitrous acid.

This spinning solution was extruded into 48% nitric acid aqueous solution at S C. and the extruded filament was stretched in a fluid state to 47 times its original length while coagulation. The filament was passed to an aqueous coagulation bath wherein it was further stretched 2 /2 times. The filament was passed into waterwashing bath wherein it was washed with water, and then it was stretched to 5 times its original length in 300 C.- superheated steam. Theproduced fiber had a strength of 6.5 gr./d., a ball mill value of 5% and a loop elonga tion of 7.8%.

Example 5 A fiber produced by following the procedures of Example 3 was subjected to relaxing treatment in steamy atmosphere having a relative humidity of 40% at 100 C. for 10 seconds, and the loop elongation of the fiber thus treated was raised to 17.3%.

On the other hand, such a fiber as prepared by any conventional method, for instance a method indicated in the last paragraph of Example 1, was subjected to relaxing under the same conditions as in above. As its result, the loop elongation of the treated fiber was depressed to 1.8% and there was observed adverse effect in such treatment.

Example 6 A copolymer of acrylonitrile containing parts of acrylamide and having an average molecular weight of 74,000 was dissolved in 67% nitric acid aqueous solution at 0 C. to have a concentration of 11%. The resulted solution was extruded into 47% nitric acid aqueous solution at 0 C. and the extruding filament was stretched ten times original length while coagulation, and then transferred to the second liquid coagulating bath consisting of the aqueous solution of 30% nitric acid at 5 C. to form a perfectly coagulated filament having gel structure, and then washed with water, and stretched 7 times by super heated steam. The produced fiber had a strength of 3.2 g./d., a ball mill value of 8% and a loop elongation of 12.0%.

When a spinning solution is prepared by dissolving polyacrylonitrile or copolymer containing at least by weight of acrylonitrile it is desirable that a solvent therefore has high solvent power for polymer and that dissolution condition of the polymer molecule in the resultant solution is very pertinent. To obtain such a spinning solution, the solvent must be one which can dissolve the polymer in higher concentration without gelling the resultant solution at lower temperature, maintaining good spinability of the solution. Such a solvent is nitric acid of 69% or more. In case the solvent is 69% or more nitric acid, the nitric acid concentration of the first coagulation bath must be 4750%. In order to improve mechanical properties of the product fiber such as loop elongation and ball mill value, the spinning solution must have viscosity more than 1000 poises.

What we claim are:

1. A method of producing shaped article from acrylonitrile polymerization product comprising at least 85% by weight of acrylonitrile, which comprises dissolving said polymerization product in nitric acid having a concentration of at least 69% so that the resultant solution has viscosity of more than 1000 poises, extruding the solution into a coagulation bath containing 47-50% nitric acid, stretching the extruded mass in the coagulation bath, washing the stretched mass with water, heat-stretching the washed mass until the molecules are orientated and then drying.

2. In the coagulation from a spinning solution and in a coagulation bath of acrylonitrile polymerization product containing at least 85% by Weight of acrylonitrile units, the improvement wherein (a) the viscosity of the spinning solution is more than 1000 poises, (b) the spinning 10 solution consists essentially of the arcylonitrile polymerization product and aqueous nitric acid solution, the concentration of nitric acid in the aqueous nitric acid being at least 69%, and (c) the coagulation bath consists essentially of aqueous nitric acid, the nitric acid concentration of said coagulation bath being from 47 to 50%.

References (Iited in the file of this patent UNITED STATES PATENTS 2,140,921 Rein Dec. 20, 1938 2,579,451 Polson Dec, 18, 1951 2,670,268 Stanton Feb. 23, 1954 2,716,586 Terpay Aug. 30, 1955 2,790,700 Stanton Apr. 30, 1957 2,878,097 Halbig Mar. 17, 1959 FOREIGN PATENTS 721,947 Great Britain Jan. 19, 1955

Claims (1)

1. A METHOD OF PRODUCING SHAPED ARTICLE FROM ACRYLONITRILE POLYMERIZATION PRODUCT COMPRISING AT LEAST 85% BY WEIGHT OF ACRYLONITRILE, WHICH COMPRISES DISSOLVING SAID POLYMERIZATION PRODUCT IN NITRIC ACID HAVING A CONCENTRATION OF AT LEAST 69% SO THAT THE RESULTANT SOLUTION HAS VISCOSITY OF MORE THAN 1000 POISES, EXTRUDING THE SOLUTION INTO A COAGULATION BATH CONTAINING 47-50% NITRIC ACID, STRETCHING THE EXTRUDED MASS IN THE COAGULATION BATH, WASHING THE STRETCHED MASS WITH WATER, HEAT-STRETCHING THE WASHED MASS UNTIL THE MOLECULES ARE ORIENTATED AND THEN DRYING.