US2287099A - Artificial wool - Google Patents

Description

Patented June 23, 1942 ARTIFICIAL WOOL Vernal R. Hardy and John B. Miles, Jn, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 7, 1938, Serial No. 183,922

29 Claims.

This invention relates to artificial fibers and fabrics and more particularly to a new synthetic wool.

This application is a continuation-in-part of our application Serial Number 125,939, filed l february 15, 1937.

In application Serial Number 125,940, filed February 15, 1937, by J. B. Miles, Jr., there are described unusual and valuable wool-like products obtained by crimping filaments derived from synthetic linear condensation polymers, particularly polyamides. The present invention is concerned with a new process for crimping such filaments which is distinguished from that disclosed in the above mentioned application in that the crimping occurs spontaneously.

An object of this invention is to prepare cold drawn wet filaments which will crimp spontaneously when dried under low tension. A further object is to prepare artificial wool-like filaments, fibers, yarns, fabrics, and the like. A further object is to prepare wool-like product having good strength, a high degree of crimp, good retentivity of crimp both wet and dry, and good heat insulating properties. A still further object is to prepare artificial fibers having a reversing helical crimp. Other objects will become apparent as the description proceeds.

These objects are accomplished by applying to suitably prepared filaments of a synthetic linear condensation polymer a treatment involving wetting with a mildswelling agent and cold drawing, as more fully described hereinafter, and then drying the cold drawn filaments under low tension, whereupon they crimp spontaneously, and if necessary setting the crimp by suitable heat treatment.

The filaments to which our new crimping process is applied and from which our new wool-like products are made, are derived from synthetic linear condensation polymers of the type dethe polymers used and to define certain terms and tests mentioned throughout the description. A property of the fiber-forming synthetic linear condensation polymers which is especially utilized in this invention is their ability to be spun into filaments which can be cold drawn into oriented filaments. The term cold drawing is applied to the process of elongating the filaments while in the solid state by the application of stress. The cold drawn filaments show definite orientation along the fiber axis whereas the undrawn filaments are substantially unoriented. The term filament as used herein will refer to both oriented and unoriented filaments or threads which are drawn from the polymers regardless of whether the filaments or threads are long (continuous) or short (staple), while the term fiber will refer more specifically to the oriented filascribed in U. S. Patents 2,071,2502,071,253 and ments (long or short). The fibers are in general more useful in the manufacture of yarns and fabrics than are the undrawn filaments. The term crimped filament or fiber will be used to indicate that the filament or fiber is not straight but possesses a crinkled, curled, spiral, helical, or serrated form.

{The term intrinsic viscosity as applied herein to polymers is defined as in which m is the viscosity of a dilute m-cresol solution of the polymer divided by the viscosity of m-cresol in the same units and at the same temperature, and C is the concentration of polymer in grams per cc. of solution. The intrinsic viscosity is indicative of the molecular weight of the polyamide. In the case of polyamides, polymers having intrinsic viscosities between 0.6 and 1.5 are in general most suitable for use in this invention. Polymers of the desired viscosity are best prepared by heating the monomeric ingredients, e. g., a diamine and a dicarboxylic acid, in the presence of a viscosity stabilizer, i. e., an agent which arrests the polymerization when a certain molecular weight (intrinsic viscosity) is reached. The point at which polymerization ceases is dependent upon the quantity of stabilizer used. Polymers prepared with the use of a viscosity stabilizer are essentially viscosity stable, i. e., they do not change materially in viscosity when heated under melt spinningconditions. Suitable viscosity stabilizing agents for the preparation of polyamides are materials such as diamines, di-

carboxylic acids, or amide-forming derivatives of dibasic carboxylic acids, which may be included as excess reactant. Monofunctional amide-forming compounds ,which include the nitrogenous bases, monobasic carboxylic acids, and amide-forming derivatives thereof may also be used as stabilizers. Sodium hydroxide, barium hydroxide, sodium acetate, ammonium acetate, etc. also function as viscosity stabilizers) Ethanolamine is also useful. The viscosity stabilizer is generally used in amounts varying from 0.5 to 3.5 molar per cent based on the polyamideforming reactants. Polymers prepared with the use of a stabilizer or mixture of stabilizers will be referred to as viscosity stable polymers.

' The term spontaneous crimping is applied to the operation in which the crimp appears in the products of this invention. This operation consists in drying in the relaxed condition suitably prepared cold drawn wet filaments. It is referred to as spontaneous crimping because the crimps appear spontaneously during the drying operation as-distinguished from crimps introduced by mechanical means or by other known methods of crimping.

The term setting as used herein will refer to any treatment which improved the permanency of the crimp in fibers. Setting usually takes the form of heating the crimped fibers with steam.

As a means of evaluation and comparison, a test has been devised to indicate the degree of permanency of the crimp. This test consists in applying a weight to the crimped fiber equivalent to 0.03 g. per denier (based on straightened length) and immersing the fiber inwater at 60 C. After 30 seconds immersion in water, the fiber is taken out, the load removed, and the fiber permitted to dry in the relaxed condition. From measurements made during this test the crimp retentivity is calculated in per cent by multiplying by 100 the quotient obtained by dividing the difference between. the initial straightened length and recovered crimped length by the difference between initial straightened length and initial crimped length. On the basis of this test the crimp retentivity of previously known artificial wools is quite low (below 40% and generally below 20%), whereas the crimp retentivity of the fibers herein described is practically 100%.

For this reason a more severe test has been devised to show'up more clearly differences between fibers produced by various modifications of the present invention. This test consists in stretching the crimped fibers until the crimps are just straightened out and then applying an additional stretch based on the length of the straightened fiber. The fibers so stretched are immersed in boiling water for 30 seconds, removed, and allowed to dry in the relaxed condition. The crimp recovery under these drastic conditions, referred to as crimp recovery from stretch, is expressed in per cent by multiplying by 100 the quotient obtained by dividing the difference between initial straightened length and recovered crimped length by the difference between initial straightened length and initial crimped length. The crimp recovery from stretch of previously known artificial wools is practically zero, whereas that of the polyamideder special conditions.

ethanol, propanol, isopropanol, or aniline.

As a result of this high crimp recovery the crimp is not lost when the fibers are made into fabrics whereas previously known artificial wools lose their crimp to a large extent during fabrication.

Having explained the various terms to be used, the invention will now be described in detail and with particular reference to synthetic linear condensation polyamides, since these polymers yield the most satisfactory artificial wool. The filaments used as starting material may be prepared from the polyamides by any method of spinning, e. g., by the melt, dry, or wet processes. filaments of almost any diameter, but filaments having deniers in the neighborhood of 0.5 to 20.0 are converted into wool-like fibers with the greatest facility. The invention can be applied to single filaments or to a plurality of filaments. In the latter case the filaments may be twisted into a thread although this affects the nature of the crimp in the final product.

The characteristic feature of this invention is the spontaneous crimping operation. Two general procedures can be employed in making the filaments susceptible to spontaneous crimping. One method consists in subjecting filaments regardless of their method of preparation to a short heat treatment (conversion), preferably while wet with an agent having a mild swelling action on the filaments, and the other method consists in spinning the filaments from melt un- The second method is a modification of the first in which conversion is effected during spinning. These methods will now be described in greater detail.

The first method, exemplified by subsequent Examples IIV, involves a heat pretreatment. This heat treatment is referred to as conversion because it converts the filaments into a form in which they are susceptible to crimping. The conversion step is applied to the filaments, either before or after the are partially cold drawn. It consists in heating the filaments for a short time in a suitable gas, vapor, or liquid.

Thus, heating in nitrogen at C. for 30 min-' utes, in steam at 150 C, for 3 minutes, or in oil at C. for one-half second are methods of conversion. To obtain the best results the filaments should be wet with a liquid having a mild swelling action on the filaments under the conditions of conversion, e. g. water, methanol, If the filaments are hot wet when subjected to conversion, the subsequent cold drawing operation must be applied after the filaments have been wetted with a mild swelling agent, dried partially, and are in the process of drying out. The preferred method of conversion is to wet the filament with a hydroxylated non-solvent for the polyamide, such as water, methanol, ethanol or isopropanol, prior to conversion and to pass the wet filament rapidly through a bath of hot liquid. As examples of suitable liquid conversion media (baths) may be mentioned hydrocarbons; chlorinated hydrocarbons; polyhydric alcohols, e. g. glycol and glycerol; esters, e. g. triacetin and castor oil; and ethers, e. g. the monobutyl ether of diethylene glycol. The conversion medium should be substantially non-volatile at the temperature and pressure used in conversion. It is desirable to select a conversion medium which is not readily miscible with the swelling agent with which the filaments are wetted and which is easily removed from the filament by wash- Wool-like fibers can be prepared from fibers have been wetted, the drawing conditions,

ing or evaporation. Metals, e. g., mercury and molten Wood's metal, can also be used as a conversion medium. Conversion can also be efiected by passing the wet filaments through a heated slot or capillary. The slot or capillary must be of sufliciently small diameter to build upapres-Y sure of the vapor with which the filaments are wetted.

The temperaturev selected for conversion and the time of contact of the filaments in the conversion medium will depend among other things on the nature of the liquid with which the filaments are wetted and the nature of the conversion medium. If conversion is to be efiected by passing water-wet filaments through hot oil, the optimum temperature range of the oil will be 140 to 165 C. and the optimum time of contact will vary from about 0.5 second at th lower temperature to 0.2 second at the higher temperature. On the other hand, if methanol-wet filaments are to be converted by heating in tetrachloroethylene, the optimum temperature range for the conversion medium is 100 to 110 C. and the optimum time of contact is from about 0.4second at 100 C. to 0.2 second at 110 C. Cold drawn filaments undergo a high degree of shrinkage to 30%) during conversion. For this reason it is necessary to adjust the rate at which the filaments are introduced into the conversion medium and removed therefrom in order to compensate for this shrinkage.

Following conversion the conversion medium adhering to the filaments is removed by washing or other suitable means. The filaments are then cold drawn.. If the filaments have been cold drawn prior to conversion cold drawing at this stage is not essential. To obtain the highest quality product, however, further cold drawing should be applied. The preferred procedure is to cold draw the filaments both before conversion (predrawing) and after conversion (afterdrawing). The degree to which the filaments are cold drawn after conversion will depend upon the extent, if any, to which they have been drawn prior to conversion. If they have not received any prior cold drawing, the best results are obtained by cold drawing the filaments from 100 to 300%. If the filaments have been predrawn, the afterdrawing should preferably be such as to make the total cold drawing from 200 to 400%. The filaments should be wet with a liquid having a mild swelling action thereon during afterdrawing, suitable liquids being hydroxylated nonsolvents, such as water and the lower boiling alcohols.

The next step in the process is the spontaneous crimping operation. This is eflected by releasing the tension on the drawn wet fibers and allowing them to dry in the relaxed condition, i. e., under low or zero tension. The tension should be released before the fibers are completely dry. During the drying of the released fibers they crimp spontaneously giving a wool-like product. A very high degree of crimp is introduced by this unique process of crimping, so that the ratio of the straightened length of the fibers or yarns to their crimped length (crimp ratio) is generally between 2 and 4. The products can therefore be stretched to a remarkable extent before the crimps straighten out. The filaments also undergo some 10 to shrinkage in straight length during crimping.

The time required for the crimp to appear varies somewhat with the nature of the polymer,

the spinning conditions, the agent with which the th time intervening between drawing and relaxation, but most of all with the rate of drying. The rate of drying of course is dependent upon the temperature and the humidity of the surrounding atmosphere. Crimping takes place at a critical stage in the drying which can be accelerated by various means, e. g., by heat, by passing a current of dry gas over ,the fibers, or by\ washing the fibers with alow boiling water-miscible liquid. The crimping time may vary from a few seconds to several minutes or longer. Usu-,

ally the crimp begins to appear when the moisture or liquid content of the fibers falls below about 4% by weight of the fiber.

The second method for imparting spontaneous crimping properties to filaments, exemplified by subsequent Examples V-IX, is carried out as follows: The first step consists in spinning a synthetic fiber-forming polyamide of relatively low or medium intrinsic viscosity, 1. e., ranging from an intrinsic viscosity of 0.6 to 1.00, and preferably between 0.65 to 0.85, from melt at a temperature as low as is consistent with smooth spinning, generally from 5 to 30 C. above the melting point of the polymer mass. Thus, for polyhexamethylene adipamide, th linear condensation polyamide derived from hexamethylenediamine and adipic acid, the preferred intrinsic viscosity and spinning temperature ranges are, respectively, 0.65-0.85 and 270-285" C.; for polydecamethylene adipamide, 0.65-0.85 and 240- 255 C.; and for 6-aminocaproic acid polymer, 0.65-0.85 and 225-245 C. Although filaments prepared in this manner can be used directly in the crimping process without any subsequent conversion step, a more highly crimped product is usually obtained if the filaments are allowed to age for at least a fewhours before subjecting them to cold drawing and spontaneous crimping.

The next operation applied to filaments prepared by the special melt spinning operation described above is to cold draw them. The filaments should be wet with a liquid having a mild swelling action thereon, preferably an hydroxylated non-solvent such as water, when they are cold drawn. The degree of swelling required is quite small. For example, water which works very satisfactorily causes only 2.5% swelling, i. e., a 2.5% increase in the dimensions of the filament. Although filaments spun under the conditions just described will exhibit the phenomenon of spontaneous crimping over the entire range of cold drawing, there is a certain range over which the finest crimp is obtained. Thus, for polyhexamethylene adipamide, the optimum degree of cold drawing is between and 350%,

i. e., until the length of the drawn fibers will be 2.5 to 4.5 times that of the original undrawn filaments. However, if the cold drawing is done in stages, it is possible to cold draw the filaments substantially completely and obtain a product having good crimp and strength.

The next step, the spontaneous crimping operation, is carried out in a manner similar to that described for the first process. It consists in drying the cold drawn wet filaments in the reexceptionally good brought about in a number of ,ways.

this remarkable phenomenon results from a difference of strain between the exterior and interior portions of the filaments. What apparently takes place when the filaments are dried in the relaxed condition is that the filament shrinks and in so doing takes on a crimp in an eiIort to relieve the difference in strain. In other words, the exterior and interior portions of the filaments appear to shrink to a different degree. (A very high degree of shrinkage occurs in drying these filaments, much higher than in the case of undrawn filaments or non-crimping cold drawn filaments.) This difierence in strain between the exterior and interior of the filaments can be For example, in the conversion method wherein filaments wet with a mild swelling medium are passed rapidly through hot oil, this difference between the exterior and interior of the filaments is probably brought about by a greater swelling action at the surface of the filament than in the interior, because the time of contact in the oil bath is too short to efiect thorough penetration of heat. In the case of longer heat treatments or of heat treatments in the absence of a swelling medium, the whole of the filament is probably affected more or less similarly and as a result the filament must be cold drawn with the exterior and interior portions at difierent moisture con tents to obtain the necessary non-homogeneous strain for crimping. This is done by wetting the filament and cold drawing it while it is drying out. Spinning from melt under the special conditions previously described also appears to give filaments which are non-homogeneous or at least become so on subsequent cold drawing. Since synthetic linear condensation polymers are crystalline, this postulated strain or non-homogeneity between the outside and inside of the filaments may be due to or relate to a difference in crystalline size or form. Owing to their crystalline character and their ready susceptibility to cold drawing, filaments of these polymers ofier unusual opportunities for bringing about this nonhomogeneity. No other type of filament ofiers this opportunity.

The crimp produced in the fibers by the process of this invention is largely helical in character, although some fiat crimps (in one plane) may also be present. The fineness of the crimp, i. e., the number of crimps per inch, depends somewhat upon the conditions under which the crimped fibers are prepared. It is not diflicult, however, to obtain products having thirty crimps per inch. Finely crimped fibers have 20 to 40 crimps per inch. As already indicated, the fibers assume a helical or curled form so that the fiber has the appearance of a coiled spring. These helices reverse their direction at irregular intervals, usually about every 0.08 to 0.4 inch in the case of finely crimped products. This is a unique fiber is not under tension. When formed into a fabric, the reversing helical crimp in the fibers is not so readily apparent.

The crimp produced by the spontaneous crimping process is sufllciently permanent to permit the use of the product in many applications. The permanency of the crimp depends in a large measure on the treatment the filaments have received prior to crimping. For example, filaments which have been subjected to conversion, e. g., by means of oil, have a higher "crimp recovery from stretc than filaments which have been rendered crimpable by the special condition of high that the setting treatment described betype of crimp not possessed by any other known artificial wool. Fine crimps have helical diameters of 0.02 to 0.08 inch, whereas the coarser crimps (4 to 6 crimps per inch) usually have helical diameters ranging from 0.15 to 0.3 inch. It should be understood that the helices are not perfeet and that their size and shape may vary considerably even within an individual fiber. In general at least four crimps per inch are required to obtain a truly valuable wool substitute. When reference is made to the number of crimps per inch it is to be understood that this refers to the number of crimps (complete turns) per inch in the fiber in its relaxed condition, i. e., when the low is unnecessary.

The crimp recovery from stretch of the polyamide fibers can be increased to a very high value by heat treatment, particularly if the heat treatment, as in the following examples, is conducted in the presence of water or other suitable setting medium. Saturated steam at to 200 C. is particularly effective. Thus, if crimped synthetic polyamide fibers are heated with saturated steam for thirty minutes at C., the crimp retentivity and the crimp recovery from stretch of the resultant fibers become practically as good as that of natural wool. Under certain conditions steam-treated polyamide fibers retain their crimp much better than does natural wool. For example, if the synthetic polyamide wool of this invention is stretched until the crimps are straightened out and an additional 10% elongation is applied, and the fiber in this condition is kept for three days under ordinary conditions and then released, substantially all the crimp returns. If natural wool is stretched under the same conditions and held only 15 hours, the crimp is substantially completely destroyed. Moreover, on long immersion in hot water under this degree of stretch, the synthetic polyamide wool retains its crimp much better than does natural wool.

As indicated in subsequent Example VI, a surprising degree of crimp setting can be effected by treating the drawn filaments with boiling water or steam before allowing them to crimp.

The following examples are illustrative of methods for practicing our invention:

Example I A 95-denier, lo-filament water-wet yarn prepared from filaments of polyhexamethylene adipamide (intrinsic viscosity 0.95), which had been drawn 100% while wet, was passed through a light mineral oil heated to 150 C. at such a rate that the time of contact was approximately one-quarter second. The oil was removed from the filaments by washing with soap and water. The yarn was then further cold drawn while still wet. The yarn was next centrifuged, washed with acetone, and passed through squeeze rolls to remove excess acetone and retained water. From the squeeze rolls the acetone-wet yarn was taken by an air aspirator which injected the yarn at a rate of 1200 ft./min. into the top of a vertical column 9 feet long and 3 inches in diameter. A current of air just insufficient to support the weight of the yarn was passed up the column. Under these conditions the yarn dried in the column and crimped spontaneously. On reaching the bottom of the column the crimped yarn was laid down on a moving endless belt traveling slower than the rate at which the yarn was laid down, so that the crimp was preserved. The belt carried the yarn through a horizontal tube filled with saturated steam at 100 C. The length of this tube was such that the yarn was in contact with steam for approximately 20 seconds. On leaving the setting tube the yarn was wound on a bobbin. It had a crimp retentivity of 100%, a crimp recovery from stretch of 60% and a tenacity of 1.6 g.

per denier based on the denier of the crimped yarn when straightened. Longer heating with steam was found to increase the crimp recovery from stretch.

Example II An undrawn 100-denier, 10-filament yarn of polyhexamethylene adipamide 'of intrinsic viscosity 0.95 was wound on a bobbin and treated with saturated steam for three minutes at 150 C. After cooling the yarn was moistened with water, dried partially, cold drawn 150% while drying out, and collected on a bobbin which was kept wet. The wet yarn was then released and allowed to dry further, whereupon it crimped spontaneously. After setting with steain the yarn had good crimp recovery from stretch.

Example III An undrawn 300-denier, 30-filament yarn of polyhexamethylene adipamide of intrinsic viscosity 0.86 was soaked in water, cold drawn 200%, and collected on a bobbin. The yarn was dried on the bobbin (1. 0. while under tension) and then soaked in methanol for about 15 minutes. The methanol-wet yarn was passed from the bobbin at a rate of 100 ft./min. through a sixinch bath containing tetrachloroethylene at 105 C. On leaving the bath the yarn was wound on a bobbin and allowed to stand until substantially free from tetrachloroethylene. The bobbin was then soaked in water and the yarn cold drawn 40%. The yarn was centrifuged and washed with acetone to remove the major portion of the water. The acetone-wet yarn was next led at a rate of 1200 ft./m1n. through squeeze rolls and then by means of an air aspirator into the top of a vertical column 9 feet long and 3 inches in diameter. The function of the aspirator was to direct the yarn away from the squeeze roll and into the vertical column. In this column the yarn dried and crimped spontaneously. On leaving the crimping column, the yarn was wound in a suitable package. The product had very high crimp, the ratio of straight length to crimped length being about 3.5. Moreover, the yarn had excellent crimp recovery from stretch (95%) so that no subsequent setting was necessary.

Eccample IV An undrawn 240-denier, 30-filament yarn of polyhexamethylene adipamide was soaked in water and then passed at a rate of 50 ft./min. through a capillary tube 4 feet in length and 0.014 inch in diameter heated to 180 C. The converted yarn was then soaked in water again, cold drawn 150%, and wound on a skein reel. The wet yarn was removed from the skein, washed with acetone, and dried under low tension. The crimped yarn obtained in this way was set by treatment with saturated steam at 120 C. for 20 minutes. The product had a high degree of crimp and excellent crimp retentivity.

Example V The polymer used in this example was viscosity stabilized polyhexamethylene adipamide having an intrinsic viscosity of 0.73, a density of about 1.1, and a melting point of 263 C. as determined in a glass tube in the absence of oxygen (248 C. when tested on heated block in air). mer was formed into filaments by extruding the molten polymer (temperature about 277 C.) under 70 lb. per sq. in. oxygen-free nitrogen pressure through a spinneret having 10 orifices each 0.0078 inch in diameter. The filaments thus formed, under the cooling action of the air into which the polymer was extruded, were collected on a bobbin at a rate of 583 ft./min. The denier of the individual filaments was about 22. After 24 hours aging at ordinary temperature, the

vbobbin containing the undrawn 10-filament thread was soaked in water and the thread cold drawn by winding it under tension on a second bobbin having a peripheral speed 3.5 times that of the first bobbin. This reduced the denier of the filaments to 6.0. The wet thread passed around the drawing bobbin once and was then immediately released. The released thread was taken from the drawing bobbin by means of an air aspirator; the thread passed into the vacuum side of the aspirator and out what is normally the air outlet tube. The thread then passed downward through a heated metal tube (inside air temperature about C.) which was five feet in length and had a gentle downward draft of air passing through it to counteract the chimney efiect. After traveling down the tube the critical point of drying was reached near the bottom. At this point spontaneous crimping occurred with the formation of a wool-like thread composed of fibers having a reversing helical crimp. On leaving the tube the crimped thread was wound loosely on a suitable bobbin.

In order to obtain low tension during winding, the thread as it left the tube was passed through a ring of glass which was perforated with a large number of holes through which a stream of air was passed. The thread tended to float through the middle of this ring and was guided onto the bobbin and traversed by the motion of the ring. The bobbin containing the crimped wool-like thread was then heated for 20 minutes at 120 C. in the presence of saturated steam to set the crimp. The thread obtained in this way had a "crimp retentivity of practically and a crimp recovery from stretch" of 82%, a tenacity of about 4 g. per denier based on the denier at break, and more than ten crimps per inch in the relaxed state.

The above thread was knitted into a fabric as follows: Six threads (10 filaments each); were twisted together four turns per inch right and then plied with a similar thread three and a half turns per inch left. Although the final denier of this wool-like yarn was about 1000, it had approximately the same diameter and bulk as a wool yarn of about 2500 denier. The synthetic yarn was knit into a piece of fabric by hand. The fabric obtained looked very much like a similar fabric knitted from natural wool yarn, i. e., it had excellent softness and an openness of structure resembling that of the wool The P y? fabric. The wool-like properties were not destroyed by washing in water. In a similar way a wool-like polyamide fabric was prepared on a circular knitting machine using a four-thread (tenfilaments each) yarn which has been twisted together ten turns per inch right under tension and plied with a similar yarn. This product resembled a similarly knitted wool fabric.

Example VI The filaments used in this example were prepared from polyhexamethylene adipamide of intrinsic viscosity 0.74 in a manner similar to that described in Example V. These. filaments, which had a denier of about 13, were soaked in water for several hours. They were then cold drawn 175% giving fibers having a denier of 4.7. While still wet the fibers were treated on a bobbin with boiling water (setting agent) for 30 minutes. They were then removed from the bobbin and dried. The released fibers crimped spontaneously during drying, yielding wool-like fibers having reversing helical crimps (30 crimps per inch). The crimped fibers were then treated for 2 minutes with air at 130 C. The crimp recovery from stretch of these fibers was approximately 90%, whereas crimped fibers similarly prepared but not subjected to a setting, treatment at any stage in their preparation had a crimp recovery from stretch of less than 10%.

Example VIl Viscosity stabilized polydecamethylene adipamide of intrinsic viscosity 0.74 and melting point 238 C. (in absence of oxygen) was spun from melt at approximately 245 C. under a pressure of 160 lb./sq. in. The spinning rate was 600 ft./min. After aging for some time, the filaments thus obtained were wet with water, cold drawn 175%, relaxed while still wet, and dried. The crimp appeared in the relaxed fibers within 20 seconds without forced drying. The ratio of straight length to crimped length of the fibers was approximately 2. Heating the relaxed fibers accelerated the appearance of the crimp, but this procedure gave fewer crimps per inch. The crimp was set in these fibers by heating them in saturated steam at 120 C. for 20 minutes. The resultant synthetic wool had a crimp retentivity" of approximately 100% and a crimp recovery from stretch of 76%. The individual fibers had a denier of 5.2, a tenacity of 2.5 g. per denier based on the denier at break, and a residual elongation of 121%.

Example VIII A 60-filament, 2.7-twist per inch yarn, prepared from undrawn filaments obtained by melt spinning ,polyhexamethylene adipamide of intrinsic viscosity 0.75 at approximately 277 C., was moistened with water and cold drawn 175%. The drawn yarn was then wound on a skein reel, the yarn being kept wet during the winding. The yarn was next removed from the reel, dipped twice in acetone, and allowed to dry. On evaporation of the major portion of the acetone and retained water, the fibers in the skein crimped spontaneously. The crimps were of the reversing helical type. Some fibers contained more crimps per inch than others, but the majority had from 20 to 40 crimps per inch. Steam was blown over the skein for a short time and then the skein was given a 20 minute setting treatment by placing it in saturated steam at 120 C. The skein was placed on a swift and unwound onto a twisting machine where the yarn was given 2.7 twists per inch. The yarn had a denier of 270 and a tenacity of 1.3 g. per denier based on the initial denier.

A yarn of this type was woven into a fabric using 60 threads per inch of spun rayon (2 ply 36's) as warp and the polyamide wool yarn as filling using a 2/2 twill 48 picks per inch weave. Another fabric was then prepared in a similar way using in place of the polyamide yarn a 1/27's (295 denier) worsted yarn. The fabrics were then given a finishing treatment which consisted in tentering followed by decatizing using 55 pound pressure steam on the drum for 10 minutes and 10 minutes drying and cooling by evacuation. The fabrics were then scoured, starting with cold water and heating to about 50 C. using a detergent for 30 minutes, followed by a hot water wash (50 C.) of 15 minutes, and a 20 minute bleaching treatment with peroxide at 50 C. After being washed again in hot and cold water, the fabrics were dried in a centrifugal wringer and dried in a hot air drier. They were then tentered for a second time. The polyamide-filled fabric compared favorably in appearance and feel with the worsted-filled fabric. The polyamide fabric was readily dyed. Moreover, it could be dyed without ill effect with indigo and the sulfanthrene type dyes with a concentration of alkali and hydrosulfite which was damaging to the worsted-filled fabric.

Example IX Polyhexamethylene adipamide of intrinsic viscosity 0.81 was spun into filaments in a manner similar to that described in Example V. The filaments, which had a denier of 18 each, were collected on a bobbin, aged for some time, immersed in water, and drawn The wet filaments were redrawn 150%, which is equivalent to a total of 400% cold drawing based on the original length. On relaxing the drawn filaments and allowing them to dry, they crimped spontaneously, yielding highly wool-like fibers having approximately 20 crimps per inch, a ratio of straight length to crimped length of 3.5, and

' a tenacity of about 5 g. per denier based o the denier at break.

Although this invention has been described with particular reference to polyamides, it is applicable broadly to fiber-forming synthetic linear condensation polymers. To obtain products useful in the textile field, however, the melting point of the polymers should be above C. so that they can be washed with boiling water. The most useful products are obtained from polymers having a melting point above 220 C. As examples of fiber-forming synthetic polymers might be mentioned polyesters, polyanhydrides, polyacetals, polyethers, polyester-polyamides, and other co-polymers. The preparation of polymers of this class is described in detail in the patents referred to above.

The fiber-forming polyamides or superpolyamides described in the above mentioned patents and in application Serial Number 74,811 are the most useful of the linear condensation polymers for conversion into the wool-like products of this invention. Of these polyamides a valuable class for use in the preparation of wool-like fibers comprises those derived fromdiamines of formula NH2CH2RCH2NH2 and dicarboxylic acids of formula HOOCCHzR'CHzCOOH or their amideforming derivatives, in which R and R are divalent hydrocarbon radicals free from olefinic and acetylenic unsaturation and in which R has a chain length of at least two carbon atoms. An especially valuable group of polyamides within this class are those in which R is (CH2): and R is (CI-12);, wherein a: and y are integers and a: is at least two. As examples of polyamides which fall within one or both of these groups might be mentioned polytetramethylene adipamide, polytetramethylene suberamide, polytetramethylene sebacamide, polypentamethylene sebacamide, polyhexamethylene adipamide, polyhexamethylene B-methyl-adipamide, polyhexamethylene sebacamide, polyoctamethylene adipamide, polydecamethylene adi-pamide, polydecamethylene pphenylene diacetamide, and poly-p-xylene sebacamide. This invention is also applicable to fiber-forming polyamides derived '"om polymerizable monoaminomonocarboxylic acids or their amide-forming derivatives, such as S-aminocaproic acid, 9-aminononanoic acid, and 11- aminoundecanoic acid. Thus, application of the process of Example V to a viscosity stable polymer of intrinsic viscosity 0.72 obtained from 6- aminocaproic acid gave a wool-like product having between 30 and 40 crimps per inch, a "crimp recovery from stretch of 78%, and a tensile strength of 4.3 g. per denier based on the denier at break. It is also within the scope of this invention to prepare wool-like fibers from mixtures of preformed polyamides and from interpolymers or co-polymers derived from a mixture of polyamide-forming reactants, e. g., a mixture of two diamines with one or more dicarboxylic acids, or a. mixture of a diamine, a dicarboxylic acid, and an amino acid.

While the wool-like polyamide fibers of our invention are in general less lustrous than unto crimping in a readily volatile liquid like acetone which is miscible with the swelling agent present. The acetone replaces the water or other swelling agent present and thus hastens the drying operation and the appearance of the crimp. Examplesof other liquids which can be used in place of acetone are methyl alcohol, ethyl alcocrimped polyamide fibers, their luster can be modified or destroyed by the addition of suitable luster-modifying agents, such as titanium dioxide and other pigments. Thus the application of the process of Example V to a polyamide containing 2% of titanium oxide gave a delustered wool-like product containing more than 20 crimps per inch, a crimp recovery from stretch of 65%, and a tensile strength of 3.5g. per denier based on denier at break. The delusterant may be added to the polyamide before or after (surface delustering) it is converted into wool-like fibers. Preferably, it is incorporated in the polyamide before it is formed into fibers. It is also possible to carry out the process of our invention using polyamides containing other types of materials, e. g., plasticizers, resins, oils, cellulose derivatives, fillers, pigments, dyes, antioxidants, etc. If a plasticizer is used, it may be removed before or after the crimping operation or it may be retained in the final product.

It is evident from the foregoing discussion and examples that a considerable degree of latitude is permitted in the mode in which the invention may be practiced. The process can be carried out as a batch process (e. g., Example V) or as a continuous process (e. g., Example I). The filaments can be crimped while moving through a drying chamber (Example I) or they can be crimped while in a stationary position, e. g., in skein form (Example VIII). Similarly the setting operation can be applied in a continuous or batch process. If desired, the setting operation, e. g., with hot water or steam, can be applied before the crimp is formed (Example VI), but preferably it is applied after the crimp is introduced (Example V).

As indicated in a number -of the examples, the wet fibers can, if desired, be soaked prior hol, isopropyl alcohol, methyl ethyl ketone, ethyl ether, dioxan, ethyl acetate, as well as mixtures of various readily volatile liquids. If the swelling agent is itself readily volatile, e, g., methanol, this step is unnecessary.

In the process of this invention it is important that the cold drawn fibers which are ready for crimping be kept moist as long as they are held under tension. However, if the fibers contain a suitable wetting agent, e. g., a sulfurized oil, they may be dried while under tension and be made to crimp by wetting them with water or other swelling agent and then releasing the tension thereon. When the relaxed fibers dry, they crimp spontaneously but in general the crimp obtained in this way is not so good as that obtained from fibers which are kept wet during the entire periodthey are susceptible to crimping.

While heating with steam is the preferred method of setting, it is within the scope of this invention to set the crimp in the fibers by other wet heat treatments. For example, hot liquids and vapors which have a mild swelling action on the fibers, 'e. g. methanol, function as setting agents. Hot water or dilute aqueous solutions of phenol or formic acid may be also employed. In fact, it is possible to use' hot aqueous solutions of a large variety of materials which do not degrade or dissolve the fibers in the concentration used. Some degree of setting can also be effected by heating the filaments while dry, e. g., at IOU- C.

While the process of this invention is applicable to filaments of synthetic linear condensation polymers generally, it will be apparent that the optimum operating conditions will vary somewhat with different filaments depending upon their properties and the manner in which they were prepared and treated. The optimum conditions for each polymer can be worked out experimentally, the essential features of the process being those outlined above.

The wool-like filaments obtained in accordance with this invention can be formed into yarns and fabrics by conventional methods with or without the addition of other filaments. Valuable yarns are obtained by plying filaments having different crimp ratios. A very useful method for forming plied yarns consists in feeding two strands of crimped filaments into a twister at different rates. This gives a yarn in which some filaments (the strand fed at the more rapid rate) have a longer straight length than the remaining filaments. This is desirable since the c-rimps do not all pull straight at the same time when tension is applied to the yarn. A novel method for securing the same effect is to ply two strands of filaments, one strand of which has been crimped and the other strand which is wet and capable of crimping on drying. After plying the yarn is dried whereupon the uncrimed strand crimps. Since the latter strand shrinks during crimping, a highly crimped yarn is obtained in which the filaments have different straight lengths and hence do not all pull straight at the same time under tension. Such yarns give especially wool-like fabrics.

The fibers of the foregoing examples are continuous. If desired, these wool-like continuous fibers can be cut into short lengths, e. g., one to six inches, and these staple fibers formed into yarns and fabrics with or without the addition of other types of staple fibers. Fabrics prepared in this way have a more fuzzy appearance and feel than those prepared from the continuous fibers. It is also possible to prepare staple woollike fibers by cutting the moist cold drawn con tinuous fibers before crimping, in which case the crimping occurs in the staple fibers. Another method for preparing wool-like staple fibers consists in drawing wet filaments capable of crimping until they break and then. drying the broken filaments to permit crimping. It is also possible to draw a bundle of filaments so as to break them into shorter lengths without destroying their parallel arrangement thus obtaining a sliver ready for spinning without the necessity of carding. Useful yarns can also be obtained by drawing a plurality of filaments until only. some of the filaments break.

Our new crimped polyamide fibers possess in addition to the desirable properties of natural wool the valuable properties characterizing the straight polyamide fibers. They show, for instance, fiber orientation when examined by Xrays. They have good resistance to solvents and chemical reagents. On heating with strong mineral acid, however, the wool-like fibers disintegrate yielding the monomeric ingredients from which they were derived. Thus, if polyhexamethylene adipamide wool is heated with hydrochloric acid, it is hydrolyzed slowly yielding adipic acid and hexamethylene diamine (as the hydrochloride). The fibers are resistant to attack by strong caustic alkalies, but these agencies also will finally hydrolyze them.

The wool-like polyamide products of this invention have wet strengths substantially equal to their dry strengths. The tenacity of the fibers generally range from 1.2 to 4 g. per denier based on the initial denier, which 'is considerably greater than that of natural wool. Owing to the great strength of our new synthetic wool, fine waips and fillings can be made: therefrom. This makes it possible to prepare fabrics of very fine thread counts (sheers) from our synthetic wool whichis not possible in the case of natural wool. The products of this invention can be dyed with the dyes used for wool. Unlike wool, the polyamides can be dyed without significant deterioration with dyes which are used in an alkaline medium. Moreover. the polyamide wool fibers and fabrics have good heat insulating properties. Since the polyamide has a lower density than wool, fabrics made therefrom are lighter than wool fabrics.

From the foregoing description it will be seen that this invention provides a convenient and economical process for the preparation of high quality artificial wool-like fibers. The outstanding feature of the process is the spontaneous crimping and the outstanding feature of the product is its unusually high crimp permanency. The products, in the case of the polyamides at least, are approximately equal to natural wool in crimp retention and heat insulating properties, and are superior to wool in strength, dyeing characteristics, heat stability, uniformity of characteristics, freedom from shrinkage, and low moisture regain. Unlike wool they are not attacked by moths. The artificial wool-like products of this invention are thermally stable at 150 0., whereas natural wool decomposes quite rapidly at this temperature with liberation of ammonia, hydrogen sulfide, and carbon bisulfide. The process by which the artificial fibers of this invention are made is of such character that modifying agents, for example, delusterants and plasticizers, can be readily incorporated therewith. As already indicated, the fibers of this invention whether long (continuous) or short (staple) can be easily formed into yarns. Thus it is possible to prepare yarns of the worsted type from these fibers. The yarns can be knitted or woven into fabrics, rugs, and the like. If desired, other types of fibers (continuous or staple, straight or crimped) or yarns, e. g., viscose rayon, acetate rayon, cotton, silk, linen and wool, can be used in conjunction with the crimped synthetic polymer fibers or yarns in the preparation of mixed fabrics" as described more fully for the polyamide wool covered in the above mentioned co-pending application by J. B. Miles, Jr. Straight synthetic polymer fibers and yarns as well as the crimped polymer fibers of the .copending Miles application can also be used with the products of the present invention. Interesting felt-like fabrics can be prepared by bringing together in a compact layer a large number of wet synthetic polymer filaments, which are capable of spontaneous crimping, and allowing them to dry and crimp in this position so that the crimps intertwine thereby holding the fibers together in a mosaic-like web. The products of this invention are also useful as down substitutes and as stufiing material for upholstery, pillows, and comforters. They can also be used in making felted articles, e. g., hats. In contrast to other known synthetic wools, the polyamide products of this invention do not lose their crimp on wetting and drying. This is a highly desirable property. A bundle of crimped polyamide fibers when wet and squeezed will spring back instead of remaining packed as will crinkled or crimped cotton, viscose rayon, cellulose acetate rayon, or any other known wool substitute. This is also true of the corresponding fabrics.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A synthetic linear polymer in the form of a crimped fiber which shows pronounced crystallinity and orientation along the fiber axis when examined by X-rays and whose crimps are preponderantly helical.

2. An artificial fiber which consists essentially of synthetic linear polymer and which has at least 4 crimps per inch and a crimp retentivity of at least 40%, said crimps being preponderantly in helices which reverse their direction at intervals along the fiber. said crimp retentivity being determined by applying 10% stretch to the straightened fiber, immersing in boiling water for 30 seconds, and drying in relaxed condition.

3. A synthetic linear condensation polymer in the form of a crimped fiber having its crimps preponderantly in helices.

4. A synthetic linear polyamide in the form of a crimped fiber having at least 4 crimps per inch and having its crimps preponderantly in helices which reverse their direction at intervals along the fiber,

5. The fiber set forth in claim 4 in which said polyamide derived from a diamine of formula NHzCHzRCHzNI-Iz and a compound of the class consisting of dicarboxylic acids of formula HOOCCHzR'CHzCOOH and amide-forming derivatives thereof, in which R and R are divalent hydrocarbon radicals and in which R has a chain length of at least two carbon atoms. 1

6. A synthetic linear polyamide in the form of a crimped staple fiber having its crimp preponderantly in helices.

7. A textile material of the class consisting of wool-like yarns and fabrics which comprise synthetic linear polyamide fibers having a helical crimp.

8. A wool-like yarn comprising synthetic linear polyamide fibers which are capable of undergoing cold drawing and which possess a helical crimp.

9. A fiber possessing a helical crimp, said fiber comprising essentially a material which yields on hydrolysis with mineral acid a diamine and a dibasic carboxylic acid- 10. A process for preparing a crimped fiber which comprises cold drawing a synthetic linear condensation polymer filament which is swollen by a mild swelling agent and in which the exterior and interior portions tend-to shrink to a different degree, releasing tension on the filament, and removing the swelling agent by drying thereby causing the filament to crimp.

11. A process for producing a wool-like product which comprises spinning a filament from a molten synthetic fiber-forming polyamide, wetting the filament with a mild swelling agent, partially cold drawing the wet filament, releasing tension thereon, and drying the relaxed filament to remove the swelling agent.

12. A process for producing crimped fibers which comprises spinning a filament from a molten mass of synthetic linear condensation polyamide of intrinsic viscosity 0.6 to 1.00 at a spinning temperature of 5 to 30 C. above the melting point of the polyamide mass, wetting the filament with an hydroxylated non-solvent for the polyamide, cold drawing the filament 50% to 300% while wet, releasing tension on the wet filament, drying it, and setting the crimp resulting therefrom by treatment with saturated steam at a temperature of 100 to 200 C.

13. In the manufacture of a wool-like product from a synthetic fiber-forming polyamide, the steps comprising heating a filament derived from said polyamide, wetting the filament with a liquid having a mild swelling action thereon, cold drawing the wet filament, releasing tension on the wet filament, and allowing it to dry thereby causing it to crimp.

14. In the manufacture of a wool-like product from a synthetic fiber-forming polyamide, the steps comprising wetting a partially cold drawn filament derived from said polyamide with a liquid having a mild swelling action thereon, passing the wet filament rapidly through a bath containing a hot liquid non-solvent for the polyamide, further cold drawing the filament while wet with a liquid having a mild swelling action thereon, and drying the filament in the relaxed condition.

15. In the manufacture of wool-like products from synthetic linear condensation polyamides, the steps comprising wetting with water filaments comprising said polyamides, heating the water-wet filaments in mineral oil at a temperature of about 140 C. to about 165 C. for about 0.5 to about 0.2 second, washing the filaments to remove retained oil, cold-drawing the filaments while wet with water, and drying the filaments in a relaxed condition.

16. In the manufacture of wool-like products from synthetic linear condensation polyamides, the steps comprising wetting filaments comprising said polyamides with methanol, heating the wet filaments in tetrachloroethylene at a temperature of about 100 C. to 110 C. for about 0.4 to 0.2 second, removing the major portion of the tetrachloroethylene, wetting the filaments with water, cold drawing them, and then drying the filaments in a relaxed condition.

17. A process for manufacturing a wool-like product from filaments of synthetic polyamide which includes the steps of wetting the filaments with a mild swelling agent therefor, cold drawing the wet filaments, releasing tension on the drawn wet filaments, and then drying the filaments in relaxed position.

18. A process for producing a wool-like prodduct which comprises spinning a filament from a molten synthetic fiber-forming polyamide at a temperature as low as is consistent with smooth spinning, wetting the filament with a mild swellswelling agent.

19. A down substitute suitable for stuffing upholstery, pillows and the like which comprises a synthetic linear condensation polymer in the form of a crimped fiber having its crimps preponderantly in helices.

20. The process of treating a synthetic yarn which comprises impregnating the yarn with a relatively low boiling swelling agent and displacing the swelling agent by a relatively high boiling lubricating agent maintained at a temperature at which the swelling agent has a high vapor pressure.

21. The process of treating a textile yarn which comprises impregnating the yarn with a relatively low boiling swelling agent and displacing the swelling agent by a relatively high boiling lubricating agent maintained at a temperature at which the swelling agent has a high vapor pressure.

22. The process of treating a synthetic yarn which comprises impregnating the yarn with a relatively low boiling swelling agent, and then treating the yarn with a relatively high boiling lubricating agent at a temperature at which the swelling agent has a high vapor pressure.

23. The process of treating a textile yarn which comprises impregnating the yarn with a relatively low boiling swelling agent, and then treating the yarn with a relatively high boiling lubricating agent at a temperature at which the swelling agent has a high vapor pressure.

24. The crimped fiber set forth in claim 9 in which said polyamide is polyhexamethylene adipamide.

25. The process set forth in claim 12 in which said polyamide is polyhexamethylene adipamide.

26. The process set forth in claim 17 in which said polyamide is polyhexamethylene adipamide.

2'7. The process set forth in claim 21 in which said yarn comprises a synthetic linear polyamide.

28. The process set forth in claim 22 in which said yarn comprises a synthetic linear polyamide.

29. The crimped fiber set forth in claim 4 in which said polyamide comprises a polymerized monoaminomonocarboxylic acid.

VERNAL R. HARDY. JOHN B. MILES, JR.