US2706674A - Melt spinning polyacrylonitriles - Google Patents

Description

United States Patent MELT SPINNING POLYACRYLONITRILES George Moore Rothrock, West Chester, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application December 12, 1950, Serial No. 200,497

20 Claims. (CI. 18-54) This invention relates to the preparation of shaped articles of acrylonitrile polymers containing at least 85% acrylonitrile and, in particular, to the spinning of yarns from a suitably plasticized polymer melt.

This is a continuation-in-part of my copending application Serial No. 64,043, filed December 7, 1948, now abandoned.

Polyacrylonitrile and copolymers of acrylonitrile in which at least 85% by weight of the polymer is acrylonitrile have been known for some time. These possess desirable physical and chemical properties including toughness, insolubility in and insensitivity to common solvents, such as water, methyl or ethyl alcohol, acetone, ethyl ether, ethyl acetate, hydrocarbon solvents, chlorinated hydrocarbons, and the like. Because of these facts numerous attempts have been made to form yarns, films and other shaped articles from these polymers. The invention of George H. Latham disclosed in U. S. 2,404,714 represents the first successful preparation of acrylonitrile polymer solutions which are suitable for the production of commercially useful textile yarns or wrapping tissues and films with similar tough, flexible properties. Various classes of organic materials which act as solvents and plasticizers for these acrylonitrile polymers are described in U. S. 2,404,7142,404,727, inclusive and in Fr. 883,764. It is disclosed in these references that the solutions of polyacrylonitrile can be converted into shaped articles by means of dry and wet spinning and casting techniques. The high molecular weight polymers, necessary for the preparation of shaped articles having outstanding physical properties, can be used in solution concentrations up to about 22% in dry and wet spinning operations. In the case of yarn preparation, the spinning speeds are limited by the rate of evaporation of the solvents in dry spinning and by the rate of coagulation of the polymer in a suitable wet spinning bath.

Formation of shaped articles from polyacrylonitrile melts, however, is exceedingly difiicult because polyacrylonitriles containing at least 85% by weight of acrylonitrile cannot be melted without decomposition. Also, materials which effectively dissolve the polymers or which plasticize them are not necessarily useful in shaping articles by melt procedures.

An object of this invention is to form shaped articles from infusible acrylonitrile polymers. A further object is the provision of a process for melt spinning infusible acrylonitrile polymers. A still further object is to produce economically and at high rates of speed acrylonitrile polymer yarns having outstanding physical properties. Other objects will become obvious from the discussions hereinafter.

The objects of this invention are accomplished by extruding through a shaped orifice into an inert atmosphere a blend of an acrylonitrile polymer containing at least 85 by weight of acrylonitrile with 4065% of a volatile organic solvent for the acrylonitrile polymers. The blends are extruded into room temperature air, solidification occurs rapidly and the filaments are drawn away from the spinneret and subsequently washed to remove the solvent. Ordinarily, the washed yarns are then colddrawn while still wet. By any one of or combination of these steps, cooling, removal of solvent or drawing, the setting of the shaped article is accomplished. The volatile organic solvent which may be used in the process of this invention may be any of those described herein or shown in the above identified patents. To mention a specific illustration, the objects of th s invention are accomplished by extruding through a shaped orifice into an inert atmosphere a blend of an acrylonitrile polymer containing at least by weight of acrylonitrile with 4065% of a cyclic organic ester containing from 3-5 carbon atoms, collecting the shaped article and subsequently washing out the ester. For example, high quality yarns may be produced in this manner. These yarns are round in cross-section, clear and tough, and may be subsequently drawn up to 11 times their original length into products having outstanding physical properties.

The process of this invention can best be understood by reference to the following examples which are illustrative and not to be construed as limitative and in which parts and percentages are by weight unless otherwise specified.

Example I A mixture of'l part of solid crystalline ethylene cyclic carbonate and 1 part of powdered polyacrylonitrile having a molecular weight of 106,000 (determined from the viscosity using the Staudinger equation) was placed in a water-jacketed Banbury mixer. The composition was mixed therein at high speed for five minutes without using the weighted cover and then mixing was continued at high speed for 30 minutes with 60-80" C. water flowing in the jacket. The resulting spinning dope was placed in an autoclave at C. from which it was forced to a metering pump. The metering pump, maintained at 142 C., delivered the spinning melt at the rate of 8 gms./min. through a standard sand pack filter to a spinneret having 10 holes, each hole having a diameter of 0.012 inch. The filaments thus produced solidified rapidly in room temterature air and were collected on a perforated bobbin at the rate of 400 yds./min. with the aid of suitable guides. Solidification was so complete that stuck filaments were not a problem. Ten bobbins of yarn were collected and washed on a single-position chuck for 30 minutes using 50 C. recirculated distilled water, allowing the solvent to build up in the wash water to about 5% by weight. The wet yarn after washing was stretched ten times its original length in a steam chamber at atmospheric pressure. The resulting oriented yarn was 1.4 denier/filament and had a dry tenacity of 4.6 grams/den. at 17% elongation. Its loop tenacity was 3.3 grams/den. at 12% elongation. The filaments are round and the yarn possesses a rather slick hand. Dry-spun polyacrylonitrile yarns are generally dog-boned in shape.

Example II The conditions described in Example I were duplicated in detail with the exception that the pump delivery was set at 12 gms./min. and the yarn was collected at the rate of 600 yds./min. After washing, the wet yarn was stretched ten times its original length in atmospheric pressure steam. The yarn was 1.35 denier/filament and had a tenacity of 5.3 gms./den. and an elongation of 18%. Its loop tenacity was 3.6 gins/den. at 13% elongation.

Example III A spinning dope comprising 52 /2% polyacrylonitrile having a molecular weight of 70,000 and 47 /2% of ethylene cyclic carbonate was prepared as described in Example I. The solution was extruded through the 10-hole spinneret, heated to C. in the manner described in Example I. The pump delivery was 20 gms./min. and the yarn was collected at 400 yds./min. The yarn was washed as described in Example I. The wet yarn was stretched ten times its original length in atmospheric pressure steam and then relaxed 14% under the same conditions. The resulting oriented yarn was 2.8 denier/filament and had a tenacity of 4.6 gms./den. and an elongation of 18%.

Example IV Monofilaments were spun from 50/50 polyacrylonitrile melts in ethylene cyclic carbonate. Clear, light tan colored monofilaments were obtained at low speed. After washing and drawing 8-11 times their original length in atmospheric pressure steam, the monofilaments were 365 denier and possessed a tenacity of 2.6 gms./den. and an elongation of 20%. Their loop tenacity was 1.4 gms./den. at an elongation of 17%.

Example V A 40/60 blend of polyacrylonitrile having a molecular weight of 70,000 in gamma-butyrolactone was prepared as described in Example I. This spinning dope was placed in a press spinner, consisting of an electrically heated cylinder to contain the polymer mixture and a heavy spinneret, which could be separately heated, mounted in the base of the cylinder. A piston operated by 600 lbs./ sq. in. oil pressure forced the material through the 5- hole spinneret (0.010 hole diameter). The cylinder was maintained at 140 C. and the spinneret was heated to 170 C. The yarn was collected after passing through 3 feet of room temperature air directly on a traversed perforated bobbin at the rate of 43 yds./ min. The yarn was washed with water to remove the solvent and then stretched 6.2 times its original length on rolls heated to 154 C. and finally heat-treated in skein form at 125 C. for one hour. The resulting oriented yarn was 34 denier/filament and possessed a tenacity of 2.7 gms./ den. and an elongation of 12%.

Example VI A 47.5/52.5 blend of polyaerylonitrile having a molecular weight of 106,000 in ethylene cyclic carbonate was prepared by the technique described in Example I and placed in the press spinner. A spinneret having but one hole of 0.047" diameter and heated to 148 C. was used. With the cylinder heated to 100 C., less than 50 lbs./sq. in. pressure on the piston was necessary to spin a filament which could be drawn without difficulty from this large hole at 10,400 in./ min. Higher wind-up speeds may be used and, accordingly, even higher spinning stretch factors are possible. The attenuation took place over a range of distance starting at the spinneret hole.

Example VII A 40/ 60 blend of polyaerylonitrile in dimethyl formamide was prepared by mixing the materials by hand at room temperature and then mixing in a Banbury mixer for 25 minutes at 50 C. This blend was spun through a five-hole spinneret (0.007 in. hole diameter) under 1,000 lbs/sq. in. pressure, the blend being at 100 C. and the spinneret heated to 150 C. The filaments were combined by means of a suitable guide and the yarn collected on a bobbin at 250 in./min. After extraction of the dimethyl formamide with water the yarn could be oriented by cold-drawing. The spinning speed may be increased to about 500 yds./min. by using temperatures at the spinneret in the neighborhood of 180 C.

Example VIII Sixty parts of a copolymer containing 95% acrylnitrile and of 2-vinylpyridine was blended for ten minutes with 40 parts of dimethyl formarnide in a Banbury mixer heated to 90 C. This blend heated to 120 C. was extruded through a single hole spinneret (hole diameter 0.015 in.) heated to 152 C. Under 800 lbs./ sq. in pressure the delivery rate of the blend through the spinneret hole was 2 g./min. The filament was collected on a bobbin at 150 yds./min. After washing with water to remove the dimethyl formamide, the filament was drawn twice its original length at 130 C. The resulting 5.5 denier filament had a tenacity of 2.5 g./ den. and the elongation at break was 9%.

Example IX A 45/55 blend of polyaerylonitrile with tetramethylene cyclic sulfone was prepared by mixing the components at high speed for 25 minutes in a heated Banbury mixer. This blend was pumped through a five-hole spinneret (hole diameter 0.010 in.) at the rate of 1 g./min. The blend was heated to 150 C. and fed through the spinneret heated to 190 C. under a pressure of 300 lbs./sq. in. The yarn was collected at the rate of 63 yds./min. After washing with water to remove the plasticizer, the yarn was drawn 8.5X at 160 C. and subsequently heat treated as a skein for 1 hour at 125 C. The 5 den./fil. yarn had a dry tenacity of 4.3 g./ den. and a break elongation of 14%.

Example X Fifty-two parts of the copolymer of Example VIII were blended with 48 parts of N-acetyl morpholine for 20 minutes at 68 C. at low speed in a Banbury mixer. This blend was heated to 125 C. and extruded through a 10-hole spinneret (hole diameter 0.005 in.) heated to 163 C. Using a pump delivery of 10 g./min., the 8.0 den./fil. yarn was collected at 660 yds./min. After washing out the plasticizer and drawing the yarn 1.8X, the yarn had a tenacity of 1.5 g./ den. and a break elongation of 22%.

Example XI Fifty-five parts of the copolymer of Example VIII having an intrinsic viscosity of 1.2 were blended with 45 parts of N-methyl-N-cyanoethyl formamide by spraying the latter material into a tumbling chamber containing the polymer at room temperature. This blend was transmitted by means of a screw extruder heated to 130 C. to a 10-hole spinneret (hole diameter 0.01 in.) heated to 190 C. The polymer remains in the screw extruder for about three minutes and was delivered from the spinneret at the rate of 6 g./min. The resulting yarn was collected on a bobbin at 200 yds./min. After extraction of the plasticizer with acetone, the yarn was drawn 10 times its original length.

Example XII The process of Example XI was repeated using 60 parts of the polymer and 40 parts of propylene cyclic carbonate. Using a feed rate of 11 g./min., the 10- filament yarn was collected at 600 yds./min.

Example XIII Repeating the blending cycle of Example XI, 60 parts of the polymer were blended with 40 parts of N,N-dimethylacetamide and extruded through a single spinneret hole (hole diameter 0.01 in.) at C. at the rate of 1.6 g./ min. The filament obtained was wound on a bobbin at 470 yds./min.

Example XIV The blending cycle of Example XI was repeated using 60 parts of the polymer and 40 parts of N,N-dirnethyl hydroxyacetamide. The blend was extruded through a 10-hole spinneret (hole diameter 0.01 in.) heated to C. at the rate of 2 g./min. The 10-filament yarn was collected at 200 yds./rnin.

Example XV The blending cycle of Example XI was repeated using 55 parts of the polymer and 45 parts of ethylene cyclic sulfite. This blend was extruded through a 10-hole spinneret (hole diameter 0.01 in.) heated to 170 C. at the rate of 10 g./min. The resulting yarn Was collected on a bobbin at 120 yds./min.

While it is disclosed in U. S. 2,404,714-2,404,727, inclusive, that solvents for polyaerylonitrile and acrylonitrile polymers containing at least 85% acrylonitrile are plasticizers for those polymers, it is not shown therein nor elsewhere that melt spinning could be accomplished. The polymers used in this invention are so high melting and so resistive to flow that melt spinning of these polymers has long been considered impossible and attempts to force polymers containing at least 85% acrylonitrile through the very small orifices in a spinneret were hitherto unsuccessful. The resistance to flow of these polymers or of previously known plasticized polymers was too great.

In addition to this, a solution of a polymer of the type used in this invention in one solvent has properties different than a comparable solution of the same polymer in a different type of solvent. When solutions of polyaerylonitrile in dimethyl formamide on the one hand and in ethylene cyclic carbonate on the other, are compared as to their utility for spinning at about 100 C. (as for instance for wet-spinning into a hot dilute aqueous bath) it is found that much lower polymer concentrations must be used in the ethylene cyclic carbonate solution than in the dimethyl formamide solution. While 22% polymer content is suitable, for example in the latter solvent, only 13% for example should be used in the former solvent to obtain an equally viscous solution. This difference carries over into the plasticized melts of this invention. The dimethyl formamide is a more efficient plasticizer than ethylene carbonate and for comparable spinnability, the dimethyl formamide/polymer blends must contain a considerably higher polymer content than an ethylene carbonate/ polymer blend of the same viscosity. The intractability of the polymers coupled with the variation in solution properties made unforeseeable the attainment of the requisite fluidity in polymer/solvent blends which are solids at ordinary temperatures. It is indeed surprising that all the blends of this invention can be melt spun under the same general conditions.

The cyclic organic esters of this invention are outstanding for producing from acrylonitrile polymers, which contain at least 85% by weight of acrylonitrile, such shaped articles, as monofilaments, multifilament yarns, films, tubings, bristles and the like. These esters, which contain from 3 to 5 carbon atoms, include such cyclic esters as ethylene cyclic carbonate, propylene cyclic carbonate, trimethylene cyclic carbonate, methylethylene carbonate, chloromethylethylene carbonate, sym-dimethylethylene carbonate, vinylethylene carbonate, tetramethylene carbonate, ethylethylene carbonate, gamma-butyrolactone, delta-valerolactone and gamma-valerolactone. Preferred among these solvents for best spinnability and high speed spinning is ethylene cyclic carbonate. Also, for economy ethylene cyclic carbonate is preferred. Blends containing as much as 60% polyacrylonitrile have been spun satisfactorily using ethylene cyclic carbonate.

The lactones and cyclic carbonates are particularly adaptable to the melt spinning technique. The melt spinning process of this invention is preferred over wet spinning because much greater speeds are attainable and much less solvent is required.

The melt spinning technique for the preparation of monofilament and multifilament yarns as described in this invention is preferred also for preparing shaped articles from polyacrylonitriles using ethylene cyclic carbonate, since the procedure allows the ready recovery of the carbonate unchanged. Cyclic carbonate solutions of acrylonitrile polymers cannot be wet spun satisfactorily into a cold water spinning bath. On the other hand, while wet spinning can be done satisfactorily in hot water baths or salt baths, hot water and aqueous solutions of electrolytes bring about the rapid decomposition of the cyclic carbonates so that they cannot be recovered unchanged. By the process of this invention the concentrated solutions of polymer are spun directly at temperatures up to and around 160 C. into room temperature air and the yarn thus formed is collected as a wound package before any solvent is removed. The solvent can then be removed readily by washing the package with cold water and no decomposition of the solvent takes place. The unchanged cyclic ester solvents can be readily recovered by vacuum distillation at 4 cm. pressure of the wash liquid to remove the water. Other materials than water could be used as extractants for the cyclic ester solvents provided they were low boiling and were not solvents for the polymer. Since the cyclic carbonates do not boil at atmospheric pressure without decomposition, the maintenance of these cyclic esters at temperatures of 160 and above for extended periods of time is to be avoided. Even though the cyclic carbonates are not distillable at atmospheric pressure, they may be distilled under reduced pressure. By the term volatile organic solvent" as used herein is meant any organic compound which dissolves acrylonitrile polymers containing at lljeast 85% acrylonitrile and which are readily vaporiza le.

For this melt spinning process the concentrations of solids in the spinning dope may be in the range 3560%. Solutions containing higher concentrations of solids, i. e., more than 60% of acrylonitrile polymer, have been spun but high speed spinning is best accomplished using concentrations less than 60%. Also, it is difficult to obtain the necessary homogeneity for satisfactory spinning using the more highly concentrated solutions. While solutions containing as low as 35% polymer have been spun by the process of this invention, there is little advantage in using the larger amounts of cyclic esters. In fact, when the polymer concentration is less than 45% by weight the filaments tend, to become tacky and to stick together unless they are coated with talc before they are collected on the perforated bobbin. Consequently, the preferred concentration of polymer in the spinning dope lies in the range of 47-53%.

Mixtures of any of the cyclic esters of this invention may be used. For example, mixtures of butyrolactone and ethylene carbonate have been used in the preparation of the spinning dope used in this invention.

It is most advantageous to draw the yarns prepared by the melt spinning technique of this invention 8-11 times their original length soon after the washing operation,

i. e., while the yarns are still wet with water. When the yarns are allowed to dry first, considerable shrinkage occurs leading to broken filaments and considerable difficulty in unwinding the package. While hot rolls can be used for this drawing operation, higher draw ratios are attainable by drawing in the presence of atmospheric pressure steam. In addition to being more economical this process involving higher draw ratios leads to correspondingly better physical properties in the final oriented yarn. An added advantage in the melt spinning process described herein is that the yarns can be readily drawn in atmospheric pressure steam. Steam under pressure is required to draw polyacrylonitrile yarns to an equal extent when prepared by the standard dry spinning techniques.

Therelaxation of oriented polyacrylonitrile yarns generally leads to the improvement in elongation of the yarn without substantial loss in tenacity. This effect as described by Silverman in U. S. 2,445,042 also applies to the polyacrylonitrile yarns prepared by the process of this invention. Again, this relaxation can be readily carried out in the presence of atmospheric pressure steam. The relaxation is not necessary but is desirable for the majority of end uses for the yarn. However, in cases where the end use requires high tenacity and low elongation it is preferable to omit the relaxation step.

It has been observed that the as-spun yarn prior to solvent removal could be drawn at room temperature at least twice its original length with the result that the surface of the filament acquired many fine transverse cracks which extended only a short distance into the filaments. This yarn after washing out the solvent can be further drawn about four times its length to give an oriented yarn of greater surface roughness than material not cold drawn. This is a means of increasing drag or surface friction of the yarn of round cross-sections. Another means of effecting inter-filament friction is by use of non-round spinneret holes. For example, crenulated filaments were prepared by spinning the concentrated spinning dopes used in the process of this invention through a spinneret having five cruciform holes 6& wide cross with 0.003" arm thickness). The spinneret spun very well at speeds equivalent to the round hole spinneret with no sticking of the filaments to the edges and produced filaments of star-shaped cross-section. The rapid solidification without removal of solvent possible by means of this invention facilitates the preparation of filaments having odd cross-sections. After drawing eight times their original length in atmospheric pressure steam and relaxing 14% in steam these star-shaped filaments possess a tenacity of 4.2 gms./den. at 15% elongation. When handled as staple, the hand of these starshaped filament yarns is distinctly scroopy as compared to the rather slick hand of round filament staple. Similarly, orifices in the shape of slots, tubes, etc. may be used to obtain other shaped articles, such as films, etc.

The invention is applicable to homopolymers and copolymers of acrylonitrile. It is particularly applicable to the preparation of shaped articles from homopolymers and copolymers of acrylonitrile containing at least 85 by weight of acrylonitrile, which polymers are difiicultly soluble and require special solvents. The invention, however, is not restricted to these difficultly soluble polymers and it can be used to advantage on the more soluble polymers containing less than 85% acrylonitrile. Thus, polyacrylonitrile and copolymers of acrylonitrile with other ethylenically unsaturated monomers, for example styrene, methyl vinyl ketone, esters of methacrylic and acrylic acids, vinyl halides and vinylidene halides, are particularly suitable for use in this invention.

It is preferred to heat the spinning dope to temperatures in the range 130 C. before it reaches the spinneret. For the best spinning performance the spinneret should be maintained at a temperature of 170 C. Pressure should be used to feed the polymer solution to the metering pump. An attempt was made to spin a 45 polymer solution on standard spinning equipment using a heated grid to melt the material ahead of the pump. However, the material would not flow through the heated grid even when held at C. for two hours. A higher temeprature would have resulted in rapid darkening. It appears that the spinning dopes of this invention are highly thixotropic and while they flow readily under considerable shear, and they do not flow by the lesser forces of gravity. The pressures required to feed the spinning dope depend upon the size of the spinneret holes. Pressures of 50 lbs/sq. in. and up to 11,000 lbs./sq. in. are required for good spinnability when using small spinneret holes. When the spinneret hole size is relatively large as in Example VI, only very low pressures, for example less than 50 lbs/sq. in., are required. In general, pressures of 200 to 1000 lbs./sq. in. are used and preferred.

High speed mixing of the well blended polymer and solvent is generally necessary to attain good spinnability. While any of the standard mixing techniques may be used, the mixing is best carried out for at least or minutes in equipment such as a Banbury mixer at temperatures between and C. When the ditficultly soluble acrylonitrile polymers containing at least by weight of acrylonitrile are used, shorter mixing cycles do not yield the necessary homogeneity for good high speed spinning. On the other hand, mixing cycles exceeding one hour lead to excessive decomposition and undue color formation. It is possible to produce highly concentrated solution of high molecular weight acrylonitrile in the cyclic ester solvent by polymerizing the acrylonitrile monomer in cyclic ester solution. This polymerization process eliminates the mixing step and avoids decomposition and discoloration which may accompany mixing.

Of effectiveness comparable to the cyclic esters are N-acetyl morpholine, tetramethylene cyclic sulfone, N,N- dimethyl formamide, N,N-dimethylacetamide, N-methyl- N-cyanoethyl formamide, ethylene sulfite and N,N-dimethyl hydroxyacetamide, as shown in the above examples. The many solvents which may be used to make the solid blends of this invention for subsequent melt spinning include N,N-dimethyl methoxyacetamide, N-formyl hexamethylene imine, p-phenylene diamine, mand pnitrophenol, succinonitrile, glycolonitrile, succinic anhydride, diglycolic anhydride, N,N-diformylpiperazine, and those disclosed in such patents as U. S. 2,404,714 to 2,404,727, inclusive, or any mixtures thereof.

It is, of course, recognized that conditions of temperature, concentration, pressure and the like will vary somewhat from solvent to solvent. In general, the conditions used for all the volatile organic solvents are those employed for the cyclic esters. The concentration of solids in the blend is in the range of about 35% to about 60% of the blend. The temperatures employed are from about C. to the decomposition point of the polymer being spun, about 230 C. for polyacrylonitrile. It is preferred to spin at temepratures below 210 C. and temperatures of about 100 C. to about 185 C. i

are generally used. Usually the blend is preheated before it reaches the spinneret and the spinneret is kept hot (about C. to about 200 C.) during the spinning. The pressures used vary from about 50 lbs/sq. in. to about 11,000 lbs/sq. in., pressures of 200 to 1500 lbs./ sq. in. being preferred. In all cases it is best to prepare the blend as rapidly as possible and at as low a temperature as possible in order to avoid decomposition or discoloration. In all cases the extruded blend is caused to solidify rapidly without appreciable removal of solvent. Extrusion is usually into an inert atmosphere having a relatively low temperature, such as room temperature. Of course, higher or lower temperatures may be used but no advantage is gained thereby in this invention. The filaments are then washed and drawn 8-11 times their original length.

Blending may be accomplished in about a half hour on a Banbury mixer at temperatures of about 60 C. to about 80 C. When this blending is used, the intrinsic viscosity and molecular weights of the polymers decrease appreciably. If high molecular weight polymers (50,000 or above) are being employed, this reduction is necessary. If the molecular weight is lower, the blends may be prepared according to the procedure in Examples 11 to 15. In this procedure very little reduction of molecular wei ht and intrinsic viscosity occurs. For the purposes of this invention the viscosity of the blend is preferably in the range of 1000 to 4000 poises at a spinning temperature of about 180 C. The molecular wei hts of the polymers are from 20000 to 50000 and the intrinsic viscosity as calculated by the Staudinger method is in the range of about 0.5 to about 1.6. All of the polymers in the blends of Examples 1 to 15 had molecular weights and intrinsic viscosities within the above ranges.

The acrylonitrile polymers can be used in the following ways, among others:

Outdoor uses:

Auto tops Balloon fabric Belts for combines Fire hose covers Horse harness Life belts and preservers Mosquito netting Rainwear Outdoor sewing thread Sporting equipment Shower curtains Camera bellows Tracing cloth Sacking Varnished thread Tapestry Varnished silk Mattress covers Tapes:

Zipper Venetian blind tapes Electrical Watch straps Rubber covered:

Coated diaphragms Conveyor belt This invention affords a highly useful and economical process for the preparation of shaped articles from acrylonitrile polymers. Yarns and monofilaments prepared by the process of this invention possess highly desirable physical properties after orientation and have high commercial utility. In contrast to the dry spinning techniques, the process of this invention requires a much smaller expenditure of solvent and no heated cell to prepare yarns having equivalent physical properties at higher speeds. Similar advantages over wet spinning techniques are obvious. Again, higher speeds are obtainable at the expenditure of less solvent and no coagulating bath is required. The cyclic ester solvents have much superior plasticizing actions when present in small quantities than most other solvents. It is, therefore, possible to spin yarns of low denier/ filament at very high spinning speeds by extruding these viscous blends or plasticized masses through spinneret holes at relatively high pressures. This melt spinning process for preparing shaped articles of polyacrylonitrile and copolymers of acrylonitrile differs from dry spinning process in that it is unnecessary to remove solvent to set up the filament since spinning into room temperature air is sufficient. In addition, the process is particularly suited to the preparation of filaments having odd shaped cross-sections, because the filaments conform better in shape to that of the orifice than in dry spinning or wet spinning procedures using odd-shaped orifices. In fact the conformance is much better than that which is attained in the melt spinning of unplasticized melts such as nylon. It also permits the use of high boiling solvents which are not useful for dry spinning.

It is surprising that the volatile organic solvents can be spun in the manner of this invention. In the first place not all solvents can be used in this process. For example, the salts of Rein U. S. Patent No. 2,140,921 or 2,117,210 cannot be used. To illustrate specifically, benzyl pyridinium chloride appears to react with the acrylonitrile polymers and serious discoloration occurs. Further, the salts are not volatile and removal of the quaternary compound leads to voids as described in Watkins U. S. Patent No. 2,426,719.

Secondly, the blends of this invention contain high amounts of solvents (40-65%) and yet they are hard, horny solids at room temperature. At first glance, they would appear to have little or no utility. This probably accounts for the fact that the blends of this invention have not been described hitherto.

Still another reason why the process of this invention is novel and leads to unexpected results is that the volatile organic solvents for the acrylonitrile polymers used in this invention come out of the spinneret orifices at elevated temperatures which are in some cases even above the boiling point of the solvent used. Yet there is no serious occurrence of surface mottling or formation of voids due to solvent removal. The behavior of the solvents in tightly adhering to the polymer molecules probably accounts in part for the intractability of the blends yet that quality is used to advantage in the spinning step involving extrusion into room temperature air or a similar atmosphere. The extrusion of the solid blends of this invention through the very small orifices to yield highly useful filaments is indeed an accomplishment.

Any departure from the above description which conforms to the present invention is intended to be inclined within the scope of the claims.

I claim:

1. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises blending said polymer with from about 40% to about 65%, based on the total weight of the resultant blend, of a volatile organic solvent for said polymer; heating said blend to a temperature of about 100 C. to about 200 C. to produce a melt; and extruding the resultant melt under pressure through a shaped orifice into an inert atmosphere which is at about room temperature.

2. A process in accordance with claim 1 in which said polymer is polyacrylonitrile.

3. A process in accordance with claim 2 wherein a pressure of 50 to 11,000 pounds per square inch is applied to said melt in said extruding.

4. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises blending said polymer with from about 40% to about 65%, based on the total weight of the resultant blend, of a volatile organic solvent for said polymer; heating said blend to a temperature of about 100 C. to about 200 C. to produce a melt; extruding the resultant melt under pressure through a shaped orifice into an inert atmosphere which is at about room temperature without appreciable loss of said solvent; and setting the resultant shaped article.

5. A process in accordance with claim 4 wherein said atmosphere is air.

6. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises blending said polymer with from about 40% to about 65%, based on the total weight of the resultant blend, of a volatile organic solvent for said ploymer; heating said blend to a temperature of about 100 C. to about 200 C. to produce a melt; extruding the resultant melt under pressure through a shaped orifice into room temperature air; washing out ihe said solvent and stretching the resultant shaped artic e.

7. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises blending said ploymer with from about 40% to about 65%, based on the total weight of the resultant blend, of a volatile organic solvent for said ploymer, to produce thereby a blend containing the acrylonitrile polymer in a form having an intrinsic viscosity of about 0.5 to about 1.6; heating said 10 blend to a temperature of about 100 C. to about 200 C. to produce a melt; and extruding the resultant melt under pressure through a shaped orifice into an inert atmosphere which is at about room temperature.

8. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least 85% acrylonitrile which comprises blending said polymer with from 40% to based on the total weight of the resultant blend, of a cyclic organic ester containing from 3 to 5 carbon atoms; heating said blend to a temperature of 100 C. to 170 'C. to form a melt; and extruding the resultant melt under pressure through a shaped orifice into an inert atmosphere which is at about room temperature.

9. A process in accordance with claim 8 wherein said polymer is polyacrylonitrile.

10. A process in accordance with claim 8 wherein said ester is a cyclic carbonate.

11. A process in accordance with claim 8 wherein said ester is ethylene cyclic carbonate.

12. A process in accordance with claim 8 wherein said ester is butyrolactone.

13. A process in accordance with claim 8 wherein a pressure of 50 to 11,000 pounds per square inch is applied to said melt.

14. A process for the preparation of shaped articles from an acrylonitrile polymer containing at least acrylonitrile which comprises blending said polymer with from 40% to 65%, based on the total weight of the resultant blend, of a cyclic organic ester containing from 3 to 5 carbon atoms; heating said blend to a temperature of C. to C. to form a melt; extruding the resultant melt under pressure through a shaped orifice into an inert atmosphere which is at about room temperature without appreciable loss of said ester; and setting the resultant shaped article.

15. A process in accordance with claim 14 in which said ploymer is polyacrylonitrile.

16. A process in accordance with claim 14 in which said ester is ethylene cyclic carbonate.

17. A process in accordance with claim 14 in which said ester is butyrolactone.

18. A process in accordance with claim 1 wherein the concentration of the polymer in said blend is in the range of about 47% to about 53%.

19. A process in accordance with claim 4 wherein the concentration of the polymer in said blend is in the range of about 47% to about 53%.

20. A process in accordance with claim 8 wherein the concentration of the polymer in said blend is in the range of about 47% to about 53%.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,714 Latham July 23, 1946 2,412,034 DAlelio Dec. 3, 1946 2,426,728 DAlelio Sept. 2, 1947 2,522,445 Ham Sept. 12, 1950 2,530,962 Hare Nov. 21, 1950 FOREIGN PATENTS 896,083 France Apr. 17, 1944

Claims (1)

1. A PROCESS FOR THE PREPARATION OF SHAPED ARTICLES FROM AN ACRYLONITRILE POLYMER CONTAINING AT LEAST 85% ACRYLONITRILE WHICH COMPRISES BLENDING SAID POLYMER WITH FROM ABOUT 40% TO ABOUT 65%, BASED ON THE TOTAL WEIGHT OF THE RESULTANT BLEND, OF A VOLATILE ORGANIC SOLVENT FOR SAID POLYMER; HEATING SAID BLEND TO A TEMPERATURE OF ABOUT 100* C. TO ABOUT 200* C. TO PRODUCE A MELT; AND EXTRUDING THE RESULTANT MELT UNDER PRESSURE THROUGH A SHAPED ORIFICE INTO AN INERT ATMOSPHERE WHICH IS AT ABOUT ROOM TEMPERATURE.