US3038240A - Composite acrylonitrile fiber with negative reversible crimp - Google Patents

Description

n 12, 1962 I F. J. KOVARIK 3,038,240

COMPOSITE ACRYLONITRILE FIBER WITH NEGATIVE REVERSIBLE CR IMP Filed Feb. 2, 1960 5 Sheets-Sheet 1 FIG.1

INVENTOR FRANK JOSEPH KOVAR IK ATTORNEY June 12, 1962 F. J. KOVARIK 3,038,240

COMPOSITE ACRYLONITRILE FIBER WITH NEGATIVE REVERSIBLE CRIMP Filed Feb. 2, 1960 3 Sheets-Sheet 2 INVENTOR FRANK JOSEPH KOVARIK ATTORNEY FIG.7

June 12, 1962 F. J. KOVARIK 3,038,240

COMPOSITE ACRYLONITRILE FIBER WITH NEGATIVE REVERSIBLE CRIMP Filed Feb. 2, 1960 5 Sheets-Sheet s HONI OBCINHLXB 83d SdWlHO INVENTOR FRANK JOSEPH KOVARIK ATTORNEY DRAW RATIO United States Patent Qfi ice 3,038,240 Patented June 12, 1962 3,038,240 CQMPGSITE ACRYLONITREE FIBER WITH NEGATIVE REVERSIBLE CRlMP Frank Joseph Kovarik, Waynesboro, Va., assignor to E. L

du Pont de Nemours and Company, Wilmington, Del,

a corporation of Delaware Filed Feb. 2, 1960, Ser. No. 6,159 4 Claims. (Cl. 28-82) This invention relates to improved crimped composite filaments and a process of making them.

Much effort has been expended towards the production of synthetic fibers which retain the well-known advantages of these fibers such as ease-of-care, durability, and improved mechanical properties, but which, at the same time, possess the properties required to obtain fabrics of outstanding aesthetic appeal such as, for example, that which characterizes wool fabrics. Wool fabrics have good bulk and cover, obtainable at a relatively low finishing shrinkage which is quite desirable from an economic standpoint. In addition, wool fabrics have excellent elastic properties such as stretchability, compressional resilience, and liveliness, and display a pleasing surface handle. Finally, the surface of wool fabrics is renewable; even after such severe deformations as crushing or glazing, a new surface can easily be obtained, for example, by wetting, steaming, or mere recovery in humid air.

It has been proposed to produce helically crimped composite filaments of synthetically formed polymers having the capacity of changing the amount of crimp upon being exposed to the effect of a swelling agent and upon reverting to the original crimp upon removal of the swelling agent. This characteristic is, for convenience, referred to as reversible crimp and is observed by the squirming of the filaments upon both application and removing of the swelling agent. The value of this crimp reversibility is evidenced by the ability of the filaments in yarns, when embodied in a fabric, to squirm or twist around in the fabric under the influence of a swelling agent such as water (and also on removal of the swelling agent), but, nevertheless, to regain the original crimp in the fabric with removal of the swelling agent, as by drying. Fabrics containing these filaments acquire a high degree of fullness or covering power as a result of the swelling treatment and retain or even increase this fullness after being subjected to such treatments repeatedly.

However, it has been found that the high degree of crimp reversibility in the fibers necessary to produce yarns and fabrics with good bulk, good compressional resilience, good response to finishing treatments, and good recovery from glazing is generally accompanied by a high level of crimp frequency. This high level of crimp frequency leads to a rough wool-like handle in knit-wear and woven-wear fabrics and does not afford soft fabrics similar to those made from cashmere, for example. For some applications, as in fabrics from woolen-spun yarns, the use of these recent fibers is restricted by a phenomenon known as pilling.

It is an object of this invention to produce a crimped composite filament having reversible crimp that affords a pill resistant fabric.

Another object is to produce a crimped composite filament having improved dyeability with dispersed dyes.

Another object is to produce a crimped composite filament having reversible crimp that affords soft, cashmerelike fabrics.

A further object is to provide a process for the preparation of the above fibers.

In accordance with the present invention a composite filament comprising at least two polymers of acrylonitrile eccentrically disposed toward each other in a side-by-side relationship is prepared having 5 to 20 helical crimps per inch of extended length, and a negative crimp reversibility of 25 to 50%, and characterized by a high resistance to pilling when spun into yarn and woven into a fabric.

The products of this invention are made by extruding in eccentric relationship at least two fiber-forming compositions of polymers of acrylonitrile, the shrinkability of one component being at least 0.2% greater than the shrinkability of the other component, and at least one of which contains 50 or more milliequivalents of ionizable groups per kilogram of polymer in excess of the ionizable groups contained in the other component, setting up the fiber structure, drawing the solidified fibers from 1.1 to 1.8x and subjecting the composite filament to the action of a shrinking agent whereby to develop crimp. By the term ionizable group is meant one capable of dissociation with the formation of positivelyand negativelycharged ions, the charges on the individual ion being due to the gain or loss of one or more electrons from the outermost orbits of one or more of their atoms.

By the expression polymer of acrylonitrile is meant the homopolymer of acrylonitrile or copolymers of acrylonitrile and monoethylenically unsaturated addition type monomers containing at least acrylonitrile. Suitable comonomers include the ethylenically unsaturated sulfonic acids as methallyl sulfonic acids and others as disclosed in U.S. Patents 2,527,300 and 2,601,256 and other monomers as disclosed in Jacobson US. Patent 2,436,926 and in Arnold U.S. Patent 2,456,360.

The two polymers selected as components must have the required difference in shrinkage and in swellability so that the composite filament crimps and a reversible crimp results. To develop crimp in the composite filaments, the shrinkability of one component should be between about 0.2 and 10% greater than the shrinkability of the other component, that is, said component has at least 0.2% greater loss of the original length upon shrink-age than the other component. However, mechanical factors such as the bending modulus, relative proportions of the components and the cross-sectional profile of the composite filament will atfect the crimp frequency to some extent, and may necessitate a variation in the shrinkage differential. With the procedures disclosed in the examples, a difference in shrinkage of between about 0.5 and 1.5% yields satisfactory results. The shrinkability of a component is determined by measuring the shrinkage, upon immersion in boiling water under no tension, of a monocomponent filament made from the component polymer (spun and otherwise processed under substantially the same conditions as the composite filament).

The shrinking of the composite filaments in order to efiect crimping, may be carried out by the use of any suitable known shrinking agent. Shrinking will ordinarily be carried out by the use of hot aqueous media such as hot or boiling water, steam or hot highly humid atmosphere, or by the use of hot air or other hot gaseous or liquid media chemically inert to the polymers of the composite filaments. The shrinking temperature is generally in the neighborhood of C. but may be higher or lower, e.g., 50 C. up to about C. or even up to a temperature not exceeding the melting point of the lowest melting polymeric component of the fiber.

Filaments produced in accordance with the present invention preferably contain about equal parts of the two components although good results may be obtained with composite filaments containing at least 20% by weight of one component and up to 80% by weight of the other component. Suitable polymers, methods for selecting them, and crimping methods are described in coassigned and copending Taylor application, Serial No. 771,677

filed November 3, 19-58. The following is a brief description of such subject matter:

The necessary differential in reversible length change between the components is readily obtained by altering the content of ionizable groups in the two polymers.

Such ionizable groups are readily obtained by copolymerizing acrylonitrile, for example, with monomers containing acid groups such as carboxylic, sulfonic or phosphonic in either the salt or free-acid form.

The following sulfonated polymerizable monomers and their salts are eminently suited for use in this invention: p-styrenesulfonic acid, methallylsulfonic acid, allylsulfonic acid and ethylenesnlfonic acid. Other examples appear in the aforementioned Taylor application.

The acidity of a polymer was determined by percolating a dimethylformamide solution of the polymer through an ion exchange column containing a mixture of a strongly acidic resin and a strongly basic resin followed by passage through a column containing the acidic resin alone. The free-acid groups in the polymer solution were then titrated using an alcoholic solution of KOI-I and a suitable indicator. The polymer concentration was determined by evaporating a portion of the solution to dryness. Analytical results were expressed as milliequivalents of acidic groups per kilogram of dry polymer.

In the following examples, which are illustrative of the invention, parts, proportions and percentages are by weight unless otherwise indicated. Also, in all the examples, the polymers were fed to the spinneret, in the form of their solutions at equal volumes.

It will be obvious to those skilled in the art that the required ionizable groups can be incorporated into a polymeric component by the blending of 2 or more polymers. The polymers should preferably be compatible.

The inclusion of from 0.5% of certain non-ionic modifiers in copolymers of acrylonitrile enhances the effect of any ionizable groups present in the final polymer. In general, it has been found that the monomers that are effective in this connection are also the same monomers which, when incorporated into an acrylonitrile polymer increases the dyeability of fibers made therefrom with a disperse dye, such as the blue-disperse dye Prototype 62.

Among the more desirable monomers from the point of view of enhancing the effect of ionizable group content are methyl acrylate, methyl methacrylate, methyl vinyl ketone, acrylamide, N-tertiarybutylacrylamide, vinyl methoxethyl ether, methoxyethyl acrylate and vinyl acetate.

TEST PROCEDURES The crimp reversibility of the filaments of this invention is determined by the following test.

A single filament is separated from the single end or tow of drawn, unrelaxed fibers. A three-inch length of the filament is attached to opposite sides of a rectangular copper wire frame with 30% slack between the ends. The rack and filament is then boiled off for 15 minutes to develop the crimp. The crimped filament is then transferred to a special viewing holder by taping or gluing the ends so that about 10% slack is present and the filament length between the clamped ends is approximately 2.5 inches. The filament and viewing holder are then mounted vertically in a stoppered test tube containing desiccant. The tube is stored vertically overnight (l8-24 hours) at 70 C. Following this conditioning period to dry the filament the tube is then brought to room temperature (approximately C.). After allowing minutes for cooling, the total number of crimps in the filament between the fixed ends are counted. In counting, any crimp reversal points present are ignored. The desiccant is then removed from the glass tube, the tube filled with water and stored vertically at 70 C. for 6 hours. The number of crimps in the wet fiber are counted as above. The cycles are repeated as required to obtain reproducible results. The equilibrium crimp reversibility (E.C.R.) or relative change in crimps/inch of extended length from Cit A 25 C. dry to 70 C. wet is obtained by the following equation.

No. of crimps (25 dry) -N0. of crimps (70 wet) X No. of crimps (25 dry) Alternatively the actual change in crimps/inch of extended length from 25 C. dry to 70 C. wet expressed as A c.p.i. may be used and is calculated as follows:

A e.p.i. (E.C.R.) (crimps dry per inch of extended length dry) 100 By extended lengtr is meant the length of a filament or yarn as measured under sufficient tension to pull out the crimp and give an essentially straight filament or yarn. All crimp counts are stated in terms of extended length.

Pilling is a well-known phenomenon of fabrics made from staple fiber yarns, and can be described as the tendency to form small clusters, clumps, or balls of interentangled fiber ends on the surface of a fabric. Pilling propensity can be measured by actual wear tests or by laboratory tests. The test described in the article Ran dom Tumble Pilling Tester by E. M. Baird et al. in Textile Research Journal 26, 731-735 (1956) is used herein.

The pilling ratings are expressed as numbers from 9 (very severe pilling) to 1 (no pilling).

Referring to the drawings:

FIGURE 1 is a central cross-sectional elevation of a spinneret assembly which can be used to make the composite filaments of this invention;

FIGURE 2 is a transverse cross-sectional plan view of the apparatus of FIGURE 1 taken at 22 thereof and showing details of the top of the back plate;

FIGURE 3 is a transverse cross-sectional plan view taken at 3-3 of FIGURE 1 showing details of the bottom of the back plate;

FIGURE 1A is an enlarged portion taken from FIG URE 1 to show details of the spinneret at the spinning orifice; and

FIGURES 4, 5, and 6 show greatly magnified crosssections, i.e., sections perpendicular to the filament axis, of typical filaments of this invention produced by dry spinning. In these drawings one component is shaded to show the separation between components.

FIGURE 7 is a graphical representation showing the relationship between crimps per extended inch obtained with particular draw ratios of a fiber as disclosed in Example I below.

With reference to FIGURE 1, the bottom spinneret plate 2 which contains a circle of orifices 3 is held in place against back plate 1 by retaining rings 12 and 14 and by bolt 13. A fine-mesh screen 4 e.g., 200 mesh per inch, is pressed into position between, and serves as a spacer between, spinneret plate 2 and back plate 1. Back plate 1 contains two annular chambers 8 and 9 which are connected to suitable piping and filtration apparatus (not shown) to receive different spinning compositions. Lead holes 11 go from annular chamber 9 to annular space 7. Lead holes 10 lead from annular chamber 8 to annular space 6. Annular spaces 6 and 7 are separated by wall 5 which is disposed above orifices 3 and spaced from spinneret plate 2 by screen 4 to permit free and contiguous passage of the spinning fiuids from annular spaces 6 and 7 through orifices 3, the mesh of screen 4 being fine enough to permit spinning fluid passage through orifices 3, as shown in detail in FIGURE 1A.

' In FIGURE 2 are shown four lead holes 10 and four lead holes 11 equally spaced within the concentric chambers 8 and 9, respectively.

In FIGURE 3 are shown the concentric inner and outer annular spaces 6 and 7, sections of bottom spinneret plate 2 and fine-mesh screen 4 partially in section.

Operation of the described apparatus in the practice of this invention is readily understood. Separate spinning materials are supplied to the inner annular chamber 9 and outer annular chamber 8, respectively, of the back plate; the former flows from chamber 9 through the lead holes 11 into the inner annular space 7 and thence through screen 4 and orifice 3 to form a part of a composite filament, while the latter passes through the lead holes 10 to the outer annular space 6 and thence through screen 4 and the outer side of the orifice 3 to form the other part of the composite filament.

The expression intrinsic viscosity with the symbol (n) as used herein signifies the value of ln(n),. at the ordinate axis intercept (i.e., when equals 0) in a graph of c as ordinate with c values (grams per 100 ml. of solution) as abscissas. (n) is a symbol for relative viscosity, which is the ratio of the flow times in a viscosimeter of a polymer solution and the solvent. In is the logarithm to the base e. All measurements on polymers containing acrylonitrile combined in the polymer molecule were made with DMF solutions at 25 C.

Example I A 20% solution in dimethylformamide (DMF) of polyacrylonitrile of (n) 2.0 and containing 27 rnilliequivalents of acid groups per kilogram of polymer (as determined by titration in a DMF solution) is simultaneously extruded as one component (which faces the center of the spinning cell) of a composite filament using a spinneret as shown in FIGURES 1-3 of the drawings. Simultaneously, a 27% solution in DMF of a copolymer of acrylonitrile/sodium styrene sulfonate 96/4% by weight composition, of (n) 1.5 and analyzing 240 rnilliequivalents of acid per kilogram of polymer is extruded as the other component (which faces the wall of the cell) of composite filaments. The spinneret contains 140 orifices 0.006 inch in diameter located on a 5.27 inch diameter circle. A mixture of carbon dioxide and nitrogen gases at 300 C. are circulated through the spinning cell, the wall of which is maintained at 180 C. The solutions are extruded at 100 C. The threadline (450 total denier) consisting of 140 composite filaments is wound up at 375 yards ,per minute (y.p.m.)

The as-spun yarn is drawn in water baths at 95 C. which extract the residual DMFfor various draw ratios. (Final length/as-spun length.) The drawn yarns are then boiled off in water for 15 minutes and the crimp intensity and crimp reversibility determined. The results are shown in FIGURE 7 which is a plot of crimps per extended inch versus draw ratio of the fiber. It is noted that the level of the crimps drops rapidly at 1.85X (it is postulated that it drops to 0). Determination of the crimp reversibility shows that all of the samples drawn to less than 1.85 have a negative crimp reversibility, i.e., they have a higher number of crimps per inch when wet than when dry whereas all samples drawn greater than 1.85 X have a positive cn'mp reversibility.

Similar results are obtained when the polyacrylonitrile is replaced with an 88/ 12 mixture (analyzing 55 meq. acid groups/kgrof polymer) of the polyacrylonitrile and the above copolymer.

Example II Composite filaments having as one component an 88/ 12 mixture (analyzing 55 rnilliequivalents of acid per kilogram of polymer) of polyacrylonitrile of (n) 2.0 and the copolymer acryloni-trile/ sodium styrenesulfonate 96/ 4 of (n) 1.5 and as a second component the above copolymer alone are prepared as in Example I. The as-spun filaments are drawn l.35 (i.e., to a length 1.35 times their as-spun length) in 95 C. water. An aqueous dispersion of a finish is applied to the drawn wet yarn at the level of 1% dry finish on yarn (dry basis). The finish-wet yarn is then mechanically crimped in a stuffer box (50 C.) similar to that shown in Hitt U.S. 2,747,233

to an extent of 5-6 herringbone crimps per extended inch. The mechanically crimped tow is then lagged in cans for two hours, out into 2 /2 inch staple, loosely arranged in a tray and dried for fifteen minutes in a circulating air oven at 130-135 C. The dry staple has a weak mechanical crimp of 56 crimps/inch plus 2 to 4 helical crimps per inch.

The staple develops nine helical crimps per inch of extended length when boiled free of restraint in water and has an E.C.R. of --50% and a A c.p.i. of 4.5 crimps/ inch. The staple has a tenacity of 0.8 g.p.d., an elongation at the break of 40%, an initial modulus of 35 g.p.d. and a denier per filament of 3.0 after boiling and drying.

For comparative purposes, fibers prepared as in Example I are drawn 4x and 2 (items b and c respectively). A further control (item d) is prepared as in Example I but using very high cell wall temperatures (250 C.) and a 4 draw ratio.

The fiber of this example (item a) and the other fibers are spun to yarns (8.5 turns per inch, Z twist, 10 cotton count (60 tex)) and knitted into fabrics (350 coursesxwales.) The properties are shown in Table I.

Yarns of item a are observed to be significantly more elastic when wet (due to the -E.C.R.) than item 0! which has a similar crimp intensity but a +E.C.R. This property enables item a to be knitted more readily wet than dry.

The superior pill resistance of the fibers of this invention as contrasted with items b, c, and d is surprising.

Sweaters knitted from the yarns of this invention have a soft cashmere-like handle when treated with a fiber lubricant whereas sweaters of similar construction from items b, c, and d when lubricated similarly have handles similar to that of wool (number grades 70s for items b and c and s for item d).

All sweaters have the excellent covering power and compressional resilience characteristic of fibers with reversible crimp.

Example III Composite filaments of the same composition as those in Example II are spun in the same manner except at 250 denier (140 spinneret orifices). The as-spun filaments are drawn 1.2 in 9698 C. water. The as-spun yarn is cut into 3% inch lengths and then dried for 15 minutes in a circulating air oven at 135 C. The dry fibers are 2% inches long.

The staple develops 9 helical crimps per inch of extended length when boiled free of restraint in water and has an E.C.R. of 50% and a A c.p.i. of 4.5 crimps per inch. The staple has a tenacity of 0.80 g.p.d., an elongation at the break of 55%, an initial modulus of 35 g.p.d. and a denier per filament of 2.0 after boiling and drying.

The fibers of this example are spun into yarn [8.5 turns per inch, Z twist, 10 cotton count (60 tex)] and knitted into fabric (350 courses wales). Wales may be defined as the number of loops per inch in a vertical column of the fabric. Courses are the number of loops per inch in a horizontal line of the fabric and perpendicular to the wales. The product of coursesXwales is a measure of the density of the knit fabric. The properties are shown in Table I, where the fabric (item e) shows a superior pill resistance to that of items b, c, and a. The knitted fabric of item 6, like that of item a, has a soft, cashmerelike handle when treated with a lubricant.

Fabrics made of fibers a and b are dyed to medium shades by disperse dyes (Colour Index Violet 4, CL Blue 3 and CI. Blue 1) under identical conditions with the following relative results:

Absolute K/S values for item a are 3.05, 3.58, and 27.44 respectively for the three dyes. The K/ S value is a measure of reflectance and is equal to in that it afiords a readily controlled way of obtaining crimped composite filaments of a low crimp level having a negative crimp reversibility and other desirable properties.

5 Blends of the fibers of this invention having a negative crimp reversibility and fibers having a positive crimp rewhere K is the absorption coefiicient as fraction of the inversibility a advantageous, Fabrics made of yarns of (lidfint energy lost y absorption P unit thickness of such blends show a superior renewability of the surface material; S is the scattering coefiicient or fraction of incift severe d f ati a crushing or glazing by wet-dry dent energy lost due to Scattering P thickness 0f treatments as contrasted to previous fabrics. Also, fabrics mat i l and R00 efi s m n h m reflectivityof the above blends also develop a higher bulk through Item 0 has a dyeability intermediate between a and b fabric-finishing steps than previous fabrics. while item d is similar to item b. What is claimed is:

The amount of y 011 a fiber the depth of 00101 1. A method for producing side-by-side composite filaapproximately Proportional to K/S Value Which ments having between 5 and helical crimps per inch is a measure of the light reflected from a sample The of extended length and having a negative crimp reversilafgef the K75 Value, the deeper the Absolute bility of between and 50%, which comprises extruding Values around are rath r deep ha s t Values of in eccentric relationship at least two fiber-forming acrylo- 100 being almost the color of the concentrated dyestufi. it il polymer components t least one of which con- Dyeability of items a and b with basic dyes is satis- 20 tains above about 50 milliequivalents of ionizable groups factory. per kilogram of polymer in excess of the ionizable groups All itfims ShOW the eXCelieht recovery flom compaction contained in the other component, drawing the solidified Cut p 1113011 Steaming and the Temoval 0f iTOIIiIIg fibers from 1.1 to 1.8 X and subjecting the composite filaglaze on fabrics by steaming that are both characteristic ment t h ti f shrinking agent, of fibers having a reversible crimp- 25 2. A side-by-side composite filament comprising at least The conditions Example III are repeated using a two acrylonitrile polymer components eccentrically dis- 20% sfiilltiol'l 0f P y for the two Components posed towards each other in the composite filament, the i the Same Chemical compojsittolt in EXamP1e III to shrinkability of one component being at least 0.2% Yleld a fiber w1th a Sectloh slmllar to FIGURE 5 greater than the shrinkability of the other component and I I other PmPertles Sumlar to the product of Example 30 one of said components containing at least 50 milliequivalents per kilogram of polymer of ionizable groups in .Altpoughfihls mventlon been Illustrated wlth dry excess of those contained by the other component, said spinning, 1t 1s, of course, applicable to filaments prepared filament havh been drawn betwe n 1 1 and 1 8 by wet spinning or plasticized melt spinning as described 3 A l g b .5 in US. Patent 2,706,674 issued to Rothrock on April 19, .two'component s! e' l? ament 1955. comprising as a first component polyacrylomtnle and as The preferred method of drawing in the process of a second component an acrylonitrile-styrenesulfonic acid this invention is in hot liquids and mpecially water at Yopolymer, Sald filament havmg f f Per 80 to The fibers can, of course, be drawn through inch of extended length and a negative equilibrium crimp steam cells or over a heated roll (100 to 200 C.) or a 40 reversibility of 25 t0 heated pin or plate 4. A composite filament in accordance with claim 3 TABLE I Pill Rating Shrinkage v R 7 am mm 32th Tenam h 5? iiz en't it he Yam, Fabric (0. X w) 20 min. 120 mm. Percent Length, Percent 1 5 113 31 3 12 +28 31 8 313 i) 7 1e 2. 0 1. 2 15 +40 7. 9 8.5 9 6 14 4. 0 2. 3 11 +40 7. a 9 3 10 1.2 0.8 9 -50 9.0 2.5 1 1 o wherein the first component is a blend of polyacrylonitrile and an acrylonitrile/ sodium styrene sulfonate copolymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,815 Sisson Apr. 20, 1948 2,572,936 Kulp et a1. Oct. 30, 1951 2,931,091 Breen Apr. 5, 1960 FOREIGN PATENTS 760,179 Great Britain Oct. 31, 1956 1,124,921 France July 9, 1956

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