US2764468A - Method of preparing resilient acrylonitrile polymer fibers - Google Patents

Description

United States Patent 70 METHOD OF PREPARING RESILIENT ACRYLO- NITRILE POLYMER FIBERS Weston Andrew Hare, Waynesboro, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application February 23, 1952, Serial No. 273,159

11 Claims. (Cl. 18-54) This invention relates to a process for spinning acrylonitrile polymers containng at least 85% by weight of acrylonitrile and in particular to the preparation of resilient yarn and fibers from suitably plasticized polymer melts.

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. The high molecular'weight polymers necessary for the preparationof shaped articles having outstanding physical properties can be used in solution concentration up to about 25% in dry and wet spinning operations. In the case of yarn preparations, the spinning speeds are limited'bythe 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 by melt extrusion methods, however, is exceedingly diflicult because polyacrylonitrile (ANP) containing at least 85% by weg'ht of. acrylonitrile cannot be melted without decomposition.

Melt extrusion methods prior to this invention have required the two separate operations of spinning and then drawing and the solvent-free fibers in the as-spun state have been weak and not suitable for textile uses, except in special applications, until drawn. The as-spun tenacity has ranged from about 0.5 to about 0.8 g. p. d. at elongations of up to By a drawing operation, in which orientation along the principal axis occurs, useful fibers are obtained having tenacity as high as 4 to 6 g. p. d. In contrast, the substantially solvent-free yarns produced by this invention may be used directly.

It is apparent that considerable economic advantage would be achieved by providing a melt extrusion process which produces useful as-spun fibers. Elimination of the necessity for a drawing operation subsequent to the normal spinning process would result in a considerable saving in both manpower and equipment and would speed up pro duction considerably. Furthermore, for a given production capacity, less space would be necessary since the floor area currently needed for drawing yarns would be eliminated.

Considerable research effort has been directed toward discovering or developing a satisfactory substitute for natural wool. A variety of synthetic fibers have been subjected to many diiferent processes, both mechanical and chemical, in an eflfort to so modify their properties that they could take the place of wool. The prior art discusses at great length the use of staple fiber-making equipment and crimpers as well as various chemical and heat treating methods for treating synthetic fibers in efforts to secure characteristics normally associated with natural wool. However, in no instance have such synthetic materials been properly classifiable as wool-like in other than superficial appearance. -A great new field wouldbe open 2,764,468 Patented Sept. 25, 1956 polymers into fibers and yarns which are tenacious in the as-spun condition and do not require asubsequent drawing operation. A further object of the invention is to provide a high speed process for spinning acrylonitrile poly= mer fibers of textile denier and to provide yarns which have the property of spontaneously crimping to a tenacious structure having the hand, resilience, and wrinkle re' sistance characteristics of fine wool. A further object is the provision of a process for converting the as-spun yarn, which is not wool-like, into wool-like materials. Other objects are obvious from the discussions hereinafter.

The objects of this invention are accompanied 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 30% to 60% of a plasticizer for the acrylonitrile polymer and cooling the extruded material until solidified into fibers while attenuating the extruded fibers by winding up or forwarding the solidified fibers to the next operation at a velocity, measured afterthe fibers have completely solidified, of at least thirty times the jet velocity. The blends are extruded into room temperature air, and solidification occurs rapidly while the filaments are drawn away from the spinneret at the required speed and subsequently washed to remove the plasticizer. The tenacious as-spun fibers or yarns are relaxed and allowed to shrink at a temperature of from'about to 200 C.; the resultant material crimps spontaneously and has the resilience characteristics of fine wool.

In preparing useful resilient yarns by this invention the following general procedure .is used. The polymer is blended with the plasticizer for the polymer, for example, in a Banbury mixer or a dough mixer, to the desired solids concentration, that is, between 40% and 70% by weight of polymer. This blend, which is a solid material at room temperature, is melted and pumped by means of a metering pump of the typecomrnonly used in the synthetic textile industry through a filter pack and spinneret orifices into'room temperature air. ments cool and solidify by passage through the air and are subjected after solidification to a means for forwarding them at a velocity of at least thirty times the jet velocity. The spinning speed, that is, the speed of the yarn at a point after complete solidification has occurred, when no more reduction in denier is observed, should be greater than 1,000 y. p. m. and may range as high as 7,000 y. p. m. and higher. It will be obvious that the speed of an extruded polymer stream will not be the same while in the fluid or semi-fluid state as it is at the windup or forwarding place. The ratio of the windup speed to the jet velocity will be referred to herein as the spin-stretch ratio. It can be calculated from the equation Vda R- W I wherein R equals the spin-stretch ratio; V is the velocity of the solid filaments in centimeters per minute; d is the density of the melt blend in grams per cubic centimeter; A is the cross-sectional area of the spinneret hole in square centimeters; and W is the extrusion rate in grams per minute per spinneret hole.

The means for forwarding the filaments may comprise a high speed wheel, roll or pinch roll, an air jet or other suitable means. Under the impetus imposed by the forwarding means, the filaments elongate in the distance be- The extruded filaification range.

tween the spinneret face and the point of complete solidification. The inertia of the material and the drag of the surrounding air apparently provides sufiicient drag on the filaments to induce orientation of the polymer molecules in the solidification range. In this solidification range, the filaments can be seen to accelerate and become taut fibers,'moving along their length at high speed. The phenomenon can further be detected by feeling the air dragged along with the filaments, beginning at the solid- It is the orientation taking place beginning at this solidification point which accounts for some of the useful properties of the resilient yarn spun by the process of this invention.

When the polymer blend is extruded into room temperature air, the resulting filaments are allowed to travel toatleast to inches before they reach the forwarding means to insure complete solidification. When the distance is less than 20 inches, fused filaments can result with an otherwise standard spinning procedure because of inadequate quenching time. This distance can be shortened, and higher speeds attained, by blowing cool air gently on the filaments just below the spinneret.

In the preparation of staple fibers, the combined filaments from a spinneret are generally forwarded by means of'an-air jet to a high speed cutter, after which the staple fibers are extracted to remove the solvent and heated to a temperature of about 90 to about 200 C. in the relaxed state.

All of the fibers and yarns prepared in accordance with the present invention are capable of spontaneous crimping. This term is applied herein to the type of crimp that appears in fibers produced by the process of this inventiorrwhen the fibers are relaxed by heating them to an elevated temperature under little or no tension, and is to be distinguished from crimp produced by mechanical means. Generally speaking, spontaneous crimping is observed whenthe yarns or fibers are heated to the vicinity of 100 C. within the broader range of 90 C. to 200 C. previously mentioned. The filaments are permitted to shrink until the fibers crimp spontaneously and generally asmuch as possible; this occurs in a very short time.

Suitable heating media used in the crimping step include hot air, hot or boiling water, saturated or superheated steam, and'various hot solutions that exert a'mild plasticizing action on the filamentary material. This heat treatmentalso'stabilizes the yarn and increases the degree of crystallization, while at the same time reducing residual shrinkage. Inthe preparation of staple fibers, the solvent laden yarn from the staple cutter may be extracted to remove the solvent and then relaxed at 90 C. to 200 C., or they may beextracted and relaxed simultaneously, for example, in hot water.

In addition to being wool-like by virtue of the crimp, yarns and fibers prepared in accordance with this invention possess a property of wool which is most difiicultto duplicate, namely, resilience. This property is not easy to measure quantitatively but may be defined to a 0011' siderable extent by three important parameters; initial tensile modulus, tensile recovery and compliance ratio.

The initial tensile modulus (represented by the symbol Mr), is defined as the slope of the first reasonably straight portion of a stress-strain curve of the funicular structure obtained by plotting tension on a vertical axis vs. elongation on a horizontal axis as the structure is being elongated at the rate of 10% per minute under a standard condition of temperature (21 C.) and humidity (60% RH). In almost every instance, this first reasonably straight portion is also the steepest slope to be found on the curve. The values as used herein are in units of kilograms per square millimeter per 100% elongation.

The initial tensile modulus, M1, is a measure of resistance to stretching and bending. The efiects of the filament modulus are felt in a fabric chiefly when the fabric is folded or crushed in the hand or otherwise handled. If the modulus is too low, the fabric is rubbery or limp; with too high a modulus in the fibers, the fabric is wiry or boardy. When the modulus is in the proper range, a soft fabric results. Attempts have been made to counteract the eifects of a modulus lying outside the wool range by a suitable adjustment of filament diameter. In each instance, this straying away from the usual diameters of wool filaments has resulted in deleterious eifects on properties such as liveliness and recovery from wrinkling. The filament properties which are almost entirely responsible for fabric resistance to bending are (l) the initial modulus and (2) the diameter, and the range of suitable diameters seems to be confined to those typical of wool. Wool-like handle is generally obtained in the fabric when fibers having an initial modulus in the wool range are used.

The tensile recovery (TR) is defined as the extent to which a yarn recovers its original length after being stretched, a stress-strain curve being used to determine tensile recovery under the testing conditions. The test consists in extending the funicular structure at a constant rate of elongation of 10% per minute. A specimen is held at the maximum elongation desired for 30 seconds, e. g., by the use of a time switch, and is then allowed to retract at the same rate at which it was extended. The same specimen is extended approximately 1.0, 3.0 and 5.0% extent for each determination. The extension during elongation and the recovery during retraction are measured along the elongation axis. The tensile recovery is then the ratio of the extent to which the yarn retracts to the extent to which it was elongated. This test is run under standard conditions at 60% R. H. and 21 C.

It is well known that resistance to wrinkling and mussing and rapid recovery from unavoidable wrinkles are highly desirable traits in apparel fabrics. The tensile recovery correlates in a high degree with these properties. The tensile recovery from a 1% elongation correlates with fabric recovery from mild wrinkling, and, as might be expected, the tensile recovery from higher elongations correlates with recovery from more severe wrinkling and sharp creasing. In this instance, the words resistance to may be used alternatively to recovery from since resistance to a crease or wrinkle really involves a very rapid and complete recovery from a crease or wrinkle when the deforming force is removed.

The compliance ratio (CR) is associated with the shape of a stress-strain curve and is a measure of the rate of change of compliance with elongation. Compliance is defined as elongation divided by tension in kg./mrn'. Hookean systems, those for which the stressstrain curve is a straight line, exhibit equal compliance at all elongations: for these the change of compliance with elongation is 0', on' the other hand one of the most important properties of wool is its change toward higher compliance as it is progressively deformed. It is this property which enables wool to feed simultaneously crisp and soft. This property is measured by determining the average rate at which compliance changes in-the range 5 to 10% elongation and is computed by the following formula:

1 (lO/tension at 10% elongation 013:5 5/tension at 5% elongation The stress-strain curve of wool has two distinctly different regions, consisting of (1) an initial portion in which the resistance to deformation is relatively great, and (2) a later portion in which the resistance decreases regularly and to a high degree. It is for this reason that a wool fabric which 'is crisp and firm to the touch will feel soft and compliant when severely crushed in the hand. Among the natural fibers this dualis'tic behavior is found only in wool and other animal hairs (not in silk, cotton, etc.), and this is one of the most attractive and valuable characteristics of wool.

In applying the above methods for evaluatingwoollike resilience, it has been found that the better grades of wool for outer garment uses have 'values for these three parameters in the following ranges:

Mi=110 to 550 kg./mm. CR=0.05 to 0.17 TR=55% or more from extensions of 3% In accordance with the process of the present invention synthetic yarns or fibers are produced which'have woollike resilience within the above limits. Furthermore, the synthetic fibers have these desirable resilience characteristics throughout the fiber length. This is accomplished by means of this invention because the filaments receive uniform treatment throughout their lengths during formation and subsequent processing' The crimping production also reducesthe tenacity and initial tensile modulus (M1), and increases the compliance ratio (CR). The effect on the M1 value becomes important at the higher spinning speeds. Frequently yarns spun at speeds near 5000 yards/minute will initially have values of M1 which are above the desired range. After the spontaneous crimping operation, however, the M1 value will have been decreased sufliciently to be within the desired range. This reduction in M1 value may be accentuated by using more severe relaxing conditions than would normally be employed, e. g., steam, glycol, glycerine or mineral oil at 160200 C., and/or longer treating times.

The process of this invention can best be understood minute and collected on a screen. The yarn was washed EXAMPLE II The results of a series of experiments are recorded in the accompanying table. The first column of the table indicates the polymer used, polyacrylonitrile being the homopolymer of acrylonitrile; copolymer A designating a copolymer containing 95% acrylonitrile and 5% of 2-vinylpyridine; copolymer B designating a copolymer containing 97% acrylonitrile and 3% of methacrylic acid; copolymer C designating a copolymer containing 95% acrylonitrile and 5% methyl acryl-ate; copolymer D designating a copolymer containing 96.8% acrylonitrile and 3.2% styrene; copolymer E denoting a copolymer containing 96.8% acrylonitrile and 3.2% methacrylonitrile; and copolymer F denoting a copolymer containing 95 acrylonitrile and 5% methyl methacrylate. The intrinsic viscosity data were obtained from dilute solutions of the polymer in dimethylformamide.

Table Polymer r Per- Per- Copolymer I. V} P1. P01. h./s. g./rn./h. y. p. In. S. R] "C. Den. Ten (gent Mi C. R. I celrziit 4 .05 TMS 52 /10 1.00 1, 370 72 50 3.8 1.20 13.3 .05 EC 58 10/10 1.00 2, 100 115 2. 7 1. 15.0 05 EC 10/10 0. 95 I l, 600 89 30 9 l. 21 18. 2 77 DMF .54 5/10 1. 60 4, 800 158 45 2. 2 1. 91 15. 3 05 TMS 54 7/14. 5 5.00 2, 100 46. 5 30 25.0 1. 05 28. 0 00 TMS 58 5/10 3. 00 7,000 123 none 2. 9 1. 20. 2 05 TMS 58 40/10 0. 67 l, 900 149 50 2. 5 1. 51 34. 0 0. TM S 58 3/10 3. 10 4, 000 68 50 5. 2 1. 42 32. 0 1.03 TMS 58 3/10 1. 93 4, 300 121 50 3. 0 1. 52 32. 7 96 TMS 58 5/10 .98 2, 400 135 50 2. 7 1. 49 35. 1 97 TMS 53 5/10 90 1, 400 94 50 3. 9 99 31. 2 1.08 TMS 58. 3/10 1. 33 3, 600 108 50 3. 4 1. 37 30. 7

gllltlllS ic viscosity. slptiedg yards/min.

as icizer. e c a 10. 3 Percent Polymer. B Extraction temperature.

4 Spinneret Holes/size. Denier/filament.

5 Delivery Rate, grams/min./hole. 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 Fifty-three parts of a coplymer containing by weight of acrylonitrile and 5% by Weight of 2-vinyl pyridine (intrinsic viscosity 1.45) and .47 parts of N- acetyl morpholine were blended together to a moist powder and then ,mixed in a 'Banbury mixer fifteen minutes at low speed using 30 C. water circulating in the mixer jacket. The mix during the first minute of mixing became a gummy mass, like milled rubber, and was heated to a temperature of about C. at the end of the cycle by virtue of the heat evolved during the mixing. The rubbery gum was removed from the mixer and charged into a press spinner cylinder equipped with a jack and a piston forapplying pressure to the gum and an external thermostatically controlled heater. A stainless steel spinneret having one hole of 0.010 inch diameter, independently thermostatically controlled, was attached to the bottom portion of the cylinder. With a temperature of C. in the cylinder and 168 C. at the spinneret, and pressure of 1500 p. s. i. on the gum producing a delivery of 1.8 grams per minute, yarn was drawn-awaybyan' air jet aspirator at 3,300 yards per Tenacity, grams/denier.

11 Percent break elongation.

11 Initial tensile modulus (kg./sq/m.m.) 13 Compliance ratio.

14 Percent tensile recovery.

Three different plasticizers were used, TMS designating tetramethylene cyclic sulfone; EC representing ethylene cyclic carbonate; and DMF symbolizing N,N-dimethylformamide. Several spinnerets ranging from 3 to 40 holes were used, the diameter of the holes being generally 10 mils or 0.010 inch. The delivery rate is recorded in grams of gum per hole per minute. The spinning speed of the yarn at the point of collection is represented in yards per minute. The spin-stretch ratio has been calculated from the equation Vda as previously defined. The density of the acrylonitrile polymers used in these experiments was 1.14 grams per cubic centimeter.

While the polymer was agitated in a dough mixer, the plasticizer was sprayed into the mixer as a fine mist. The resulting pre-mix was a coarse, slightly damp-feeling powder. A standard Royle plastics extruder, fitted With a metering screw, was used to convert the powder pre-mix to a gum and to meter the gum through sand packs to the spinneret. The rear section of the extnlder was kept nea-r room temperature to avoid premature gumming of the pre-mix and consequent difliculty in feeding. The forward section of the extruder was heated to about C. An adapter containing the filter packs and the spinneret was fitted to the front of the extruder. This adapter was held at the spinning temperature of 190$ C. The filter pack consisted of an upper layer of V2" of 60 to 80 mesh sand and a lower layer of /2" of 100 to 150 mesh sand.

The pro-mix was fed to the hopper of the extruder and with the screw turning at about revolutions per minute, the pre-mix was converted to gum and delivered under a pressure of about 8,000 p. s. i. to the spinneret. The extrudedfilaments were passed through an air jet which accelerated them to the desired speed. A. flying knife cutter was used to cut the thread line into staple fibers of about 3" in length. The cut staple was collected in a basket and transferred as a batch to a water extraction bath. As recorded in the accompanying table, the extraction temperatures ranged from room temperature to 50 C., the extraction being for a period of one hour. Following extraction the staple was boiled in water for a period of one hour. During the boil-off, the staple crirnped spontaneously.

The results illustrated in the above table demonstrate that the process of this invention is applicable to both acrylonitrile homopolymer and copolymers with other polymerizable ethylenically unsaturated monomers in a range of compositions with various plasticizers for the polymers. The spinning conditions of gum delivery and yarn speed leading to spin stretch ratios above thirty cover a wide range. The resilience properties of the products are all well within the fine wool range. The tensile strengths of the products are generally higher at the high spin stretch ratio.

While it is disclosed in U. S. 2,404,714 to 2,404,727, inclusive, that solvents for polyacrylonitrile and acrylonitrile polymers containing at least 85 by weight of 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 very small orifices in a spinneret were hitherto unsuccessful.

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 polyacrylonitrile in dimethylformamide 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 hotdilute aqueous bath) it is found that much lower polymer concentration must be used in the ethylene cyclic carbonate solution than in the dimethylformamide 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 dimethylformamide is a more efiicient plasticizer than ethylene carbonate and the dimethylformamide/ polymer blend 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/plasticizer blends which are solid at ordinary temperatures. It is indeed surprising that all the blends of this invention can be melt spun under the same general conditions. For this melt spinning process, the concentration of solids in the spinning dope may be in the range of 40% to 70% by weight. Blends containing higher concentrations of solids, that is, more than 70% of acrylonitrile polymer, have been spun but high speed spinning is best accomplished using concentrations less than 70%. Also, it is difiicult to obtain the necessary homogeneity for satisfactory spinning using a more highly concentrated blend. While blends containing as low as polymer have been spun by the process of this invention, there is little advantage in using the larger amounts of plasticizer. In fact, when the polymer concentration is less than by weight, the filaments tend to become tacky and they stick together unless they are coated with ta-lc before they are collected. Consequently, the preferred concentration of polymer in the spinning dope'lies in the range of to 58%.

The filaments prepared by the process of this invention conform well to the shape of the spinneret hole. Thus, round filaments are obtained from the ordinary circular-hole spinneret. This is in contrast to the results obtained when using the same spinneret for wet spinning or dry spinning of .acrylonitrile polymer solution. Dry spinning generally yields. filaments which are dog-boned in cross-section while wet spun filaments are generally crenulated. Interfilament friction, can be obtained by spinning filaments having no-round cross-section from non-round spinneret holes. For example, filaments were prepared by spinning the concentrated spinning dope used in the process of this invention through a spinneret having five cruciform holes GA wide cross with 0.003" arm thickness). The spinneret performed very well at speeds equivalent to the round hole spinnerets with no sticking of the filaments to the edges and produced filaments of star-shaped cross-section. When handled as staple, the hand of these star-shaped filament yarns is distinctly scroopy as compared to the rather slick hand of round filament staple.

It is preferred to heat the spinning dope to temperatures in the range -150" C. before it reaches the spinneret. For the best spinning performance the spinneret should be maintained at a temperature of -205 C. and preferably at 180 C.-l90 C. Pressure should be used to feed the polymer solution to the metering pump. For example, an attempt was made to spin a 45% polymer dope on standard spinning equipment using a heated grid to melt the material ahead of the pump. However, the material would not flow under gravity through the heated grid even when held at C. for two hours. A higher temperature would have resulted in rapid darkening. The spinning dopes of this invention display non-Newtonian flow charactistics and they flow readily only under considerable shear. The pressures required to feed the spinning dope depend principally upon the composition of the filter pack. Pressures of 50 lbs/sq. in. and up to 11,000 lbs/sq. in may be used for good spinnability, depending upon the eificiency of filtration desired. When a coarse sand filter pack is employed, only very low pressures, for example less than 50 lbs./ sq. in., are required. Filtration of the melted gum is necessary and the pressure required to feed the spinning dope should, of course, be adjusted to afford the desired delivery rate.

Well blended melts are used to attain good spinnability. Any of the standard mixing techniques may be used, for example, the mixing may be carried out for about 15 to 30 minutes in equipment such as a Banbury mixer at temperatures between 30 and 100 C. When the difiicultly soluble acrylonitrile polymers containing at least 85% 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. The'method described in Example II has been found highly satisfactory. Again. it is possible to produce highly concentrated mixtures of high molecular weight acrylonitrile in the plasticizer by polymerizing the acrylonitrile monomer in a dispersion of the plasticizer. Blended polymer/plasticizer mixtures are attained directly. This-polymerization process eliminates the mixing step and avoids decomposition and discoloration which may accompany mixing.

, The-many plasticizerswhich may be used to make the solid blends of this invention for subsequent melt spinning include N-acetyl morpholine, ethylene cyclic carbonate, tetramethylene cyclic sulfone, N,N-dimethyl formamide, N,N-dimethylacetamide, N-methyl-N-cyanoethyl formamide, ethylene sulfite, N,N-dimethyl hydroxyacetamide, N,N-dimethy1 methoxyacetamide, N-formyl hexamethylene imine, p-phenylene diamine, mand pnitrophenol, succinonitrile, glycolonitrile, succinic anhydride, diglycolic anhydride, N,N'-diformylpiperazine, and any of the materials disclosed as solvents in such patents as U. S. 2,404,714 to 2,404,727 inclusive or any mixtures of the above substances.

Mixtures of any of the plasticizers 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.

By acrylonitrile polymers containing at least 85% by weight is meant the homopolymer, polyacrylonitrile, and those copolymers of acrylonitrile in which at least 85% by weight is derived from acrylonitrile. In the copolymers the remaining is derived from monomers copolymerizable with acrylonitrile. These are generally ethyleneically unsaturated monomers such as styrene,

methyl vinyl ketone, esters of methacrylic and acrylic acids, vinyl halides and vinylidene halides such as, vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride and vinylidene chlorofluon'de, vinylidene cyanide, butadiene, vinyl pyridine acrylamide, N-monoand disubstituted acrylic amides, vinyl ethers and the like. The polymers may be prepared by any of the well-known polymerization processes such as those contained in U. S. Patents Nos. 2,436,926, 2,486,241, 2,491,471 and 2,546,238. The monomers are added in the polymerization as reactants and dior tri-component, or even more, copolymers may be made and used in this invention. Also, non-acrylonitrile monomer may be polymerized separately and blended with polyacrylonitriles. In either case, the amount of modifier in the final polymeric material should not exceed 15 by weight.

It is, of course, recognized that conditions of temperature, concentration, pressure and the like will vary somewhat depending on the plasticizer and the polymer being used. But in general, the conditions used are about the same. The concentration of solids in the blend is in the range of about 40% to about 70% of the blend. The temperatures employed are from about 140 C. to about 230 C. It is preferred to spin at temperatures below 200 C. and temperatures of about 180 C. to about 190 C. are generally used. 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, such as air, 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 heated in a free-to-shrink condition at about 90 C. to about 200 C. for a short time.

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 method 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 helpful to spinning. If the molecular weight is lower, the blends may be prepared by spraying the plasticizer into a tumbling chamber containing the polymer at room temperature. In this procedure the blend is then transmitted to the spinneret by means of a screw extruder heated to 100 C.l30 C. and very little reduction of molecular weight and intrinsic viscosity occurs. For the purposes of this invention the viscosity of the blend is preferably in the range of about 1,000 to about 4,000 poises at a 10 spinning temperature of about 180 C. The molecular weights of the polymers'are from about 20,000 to about 50,000 and the intrinsic viscosity as calculated by the Staudinger method is in the range of about 0.5 to about 1.6.

As long as the spin-stretch ratio, as defined previously is maintained at 30 or above, the spinning speed may be varied over a wide range depending upon the exact properties of the yarn desired. In general, the minimum speed to obtain a wool-like product in addition to a tenacity of at least one gram per denier will be about 1,000 y. p. m. The higher spinning speeds result in yarn with higher tenacity and lower shrinkage and, speeds ranging up to 7,000 y. p; m. and higher have been achieved. Fibers which have the appearanceand resilience characteristics of wool, upon hot water or hot air relaxation, are obtained over the whole range of spinning speeds, from 1,000 y. p. m. on up. A critical feature is the spin-stretch ratio. If this ratio isbelow'30, the products obtained do not have the desirable strength and resilience characteristics.

The spinning speeds essential in the process of this invention may be obtained by several methods. A driven bobbin, a high speed pirntake-up or an air jet may be used as a tensioning and forwarding device wherein the yarn together with other yarns to form a tow, can be forwarded directly to a staple cutter or to a crimper without an intermediate windup.

The plasticizer may be removed from the spun yarn by leaching it out with a solvent for the plasticizer but a non-solvent for the yarn. While water is generally preferred as the extractant for economic reasons, other materials such as acetone, alcohol, ether, chlorinated hydrocarbons and the like can be employed. It is sometimes convenient to apply finish to the yarn or staple during extraction by incorporating a minor amount of the finish in the extracting liquor. The final properties are relatively unafiected by the temperature of the extraction as long as that temperature is below about C. Extraction temperatures above 80 C. generally produce yarns having somewhat lower tenacity, lower initial modulus and slightly higher compliance ratio. Although these yarns are'still useful and have the Wool like properties, the higher temperatures are not used. In general, extraction is effected with water at about 50 0, since better yarn properties are obtained and the process is cheaper.

The fibers prepared by means of the process of this in-' vention can be crimped spontaneously by treatment in the relaxed state in water at about C. to about C. or in hot air at about 95 C. to about 200 C. Fibers: which shrink from 15% to 30% crimp well when supported on a solid surface, for example, a moving belt in. an oven. The preferred method of crimping is to support the fibers by a current of air heated to from 95 C. to 200 C. This method of crimping is highly effective and rapid. By this method, fibers having shinkages as low as 3% and as high as 30% or higher can be crimped satisfactorily in a few seconds. A convenient method is to blow staple fibers through a pneumatic tube fed with hot air at a temperature of about C. Another convenient method is to expose the fibers to a boiling water shower for a few seconds.

The particular fibers prepared by the process of this invention not only duplicate fine wool fibers in appearance, but in the important physical characteristics of initial tensile modulus, tensile recovery and compliance ratio. As a result, a wool-like fabric may be produced from them which is crisp and firm to the touch and, nevertheless, feels soft and compliant when severely crushed in the 'hand. These fibers and yarns of acrylonitrile polymer materials possess, in addition, much greater strength and wear resistance than Wool fibers and are not attacked by moths.

Fabrics made from these fibers are lively and wrinkle resistant, with desirable drape and excellent crease retentivity. They are remarkably insensitive to water and changes in humidity. Also of importance is the versatility'which the fibers possess over and above that of wool for processing into fabrics. They are useful, particularly in staple form, in felts of various kinds, including papermakers felts, carpets, mens and womens suits, bathing suits, sweaters, knitting yarns, as the warp in Turkish towels and the like.

Suiting fabrics prepared from the staple fibers produced in accordance with this invention are particularly outstanding. These are equal to or better than high grade woolen suiting fabrics in wrinkle resistance, recovery from wringling, and retention of ironed creases. Trousers may be cleaned by washing in an automatic washer and hanging them up to dry; they do not shrink appreciably, retain their original creases, and need no further pressing.

This invention affords a highly useful and'economical process for the preparation of fibers and yarns from acrylonitrile polymers which possess highly desirable physical properties 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; lower investment is involved; a higher output per spinning position is attained and the amount of handling is reduced. Orientation by subsequent cold-drawing'is eliminated. Similar advantages over wet spinning techniques are obvious. Again, higher speeds are obtainable and less materials cost is involved it the plasticizers are used in relatively small amounts and no coagulating bath is required. It is 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. 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 plasticizers which are solvents but are not particularly useful for dry spinning because of their high boiling points,

From the above disclosure, it is seen that the present invention provides a high speed direct method for spinning fibers and yarns of acrylonitrile polymers in a condition in which the fibers or yarns will crimp spon' taneously to desirable resilient structures. The process accomplishes this result without the necessity of a subsequent drawing operation. The fibers or yarns may be passed directly from the spinning operation to the washing and crimping operation to form highly useful fibers or yarns in a continuous operation.

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

I claim:

1. A process for producing wool-like filaments which comprises blending a polymer of acrylonitrile, at least by Weight of Which is derived from acrylonitrile, with a plasticizer for said polymer to produce a blend containing about 30% to about 60% of said plasticizer; extruding, by application of heat and pressure, said blend through a shaped orifice into an inert atmosphere; cooling the resultant filaments and pulling them away from said orifice at a forwarding velocity of the solidified filament of at least thirty times the jet velocity used in said extrusion: washing the filaments to remove said plasticizer; and relaxing and shrinking the filaments at a temperature of about C. to about 200 C.

2. A process in accordance with claim 1 in which the said relaxing and shrinking is done in a medium comprising air.

3. A process in accordance with claim 1 in which the said relaxing and shrinking is done in a medium comprising water.

4. The process of claim 1 in which the filaments are pulled away from the said orifice at a speed of at least 1000 yards per minute.

5. The process of claim 1 in which the material is pulled away from said orifice at a speed of about 1000 yards per minute to about 7000 yards per minute.

6. The process of claim 1 in which the blend is extruded at a temperature of about C. to 230 C. at a pressure of from about 50 p. s. i. to 11000 p. s. i.

7. The process of claim 1 in which the polymer is polyacrylonitrile.

8. The process of claim 1 in which the polymer is a copolymer ofacrylonitrile and an ester of acrylic acid.

9. The process of claim 8 in which the polymer is a copolymer of acrylonitrile and methyl acrylate.

10. The process of claim 1 inwhich the plasticizer is tetramethylene cyclic sulfone.

11. The process of claim 1 in which the plasticizer is N,N-dimethylformarnide.

References Cited in the file of this patent UNITED STATES PATENTS 2,404,722 Houtz July 23, 1946 2,426,728 DAlelio Sept. 2, 1947 2,437,263 Manning Mar. 9, 1948 2,522,527 Manning Sept. 19, 1950 2,585,499 Rothrock Feb. 12, 1952 2,604,667 Hebeler July 29, 1952

Claims (1)

1. A PROCESS FOR PRODUCING WOOL-LIKE FILAMENTS WHICH COMPRISES BLENDING A POLYMER OF ACRYLANITRILE, AT LEAST 85% BY WEIGHT OF WHICH IS DERIVED FROM ACRYLONITRILE, WITH A PLASTICIZER FOR SAID POLYMER TO PRODUCE A BLEND CONTAINING ABOUT 30% TO ABOUT 60% OF SAID PLASTICIZER; EXTRUDING, BY APPLICATION OF HEAT AND PRESSURE, SAID BLEND THROUGH A SHAPED ORIFICE INTO AN INERT ATMOSPHERE; COOLING THE RESULTANT FILAMENTS AND PULLING THEM AWAY FROM SAID ORIFICE AT A FORWARDING VELOCITY OF THE SOLIDIFIED FILAMENT OF AT LEAST THIRTY TIMES THE JET VELOCITY USED IN SAID EXTRUSION; WASHING THE FILAMENTS TO REMOVE SAID PLASTICIZER; AND RELAXING AND SHRINKING THE FILAMENTS AT A TEMPERATURE OF ABOUT 90* C. TO ABOUT 200* C.