US3798296A - Spinning self-crimping composite fibers - Google Patents

Abstract

SELF-CRIMPING COMPOSITE FIBERS OF ACRYLONITRILE POLYMER COMPONENTS, ALL OF THE SAME ACRYLONITRILE POLYMER BUT SOME OF WHICH CONTAIN FINELY DISPERSED SILICA PARTICLES TO REDUCE SHRINKAGE THEREOF AND THE REST OF WHICH CONTAIN WATER-INSOLUBLE PLASTICIZER, E.G., ORGANIC PHOSPHATE OR PHOSPHITE TO INCREASE SHRINKAGE THEREOF AN EXPOSURE TO HEAT SO CRIMP IS DEVELOPABLE AT ELEVATED TEMPERATURE. SUCH FIBERS ARE MADE BY PREPARING A PLURALITY OF POLYMER SOLUTIONS OF THE SAME POLYMER AND THE SAME POLYMER CONCENTRATION, DISPERSING FINELY DIVIDED SILICA PARTICLES IN SOME BUT NOT ALL THESE POLYMER SOLUTIONS, DISPERSING A WATER-INSOLUBLE LIQUID PLASTICIZER IN THE REST OF THE POLYMER SOLUTIONS, AND SPINNING SUCH SPINNING SOLUTIONS TO FORM COMPOSITE FIBERS BY A PROCESS WHICH INCLUDES THE STEPS OF STRETCHING THE FIBERS AND SUBSEQUENTLY RELAXING THE FIBERS AT ELEVATED TEMPERATURE IN A FREE-TO-SHRINK CONDITION TO DEVELOP CRIMPINESS THEREIN.

Description

3,798,296 SPINNING SELF-CRIMPING COMPOSITE FIBERS James Kellett Thomas, Pensacola, Fla., assignor to American Cyanamid Company, Stamford, Conn. No Drawing. Filed July 28, 1972, Ser. No. 276,192 Int. Cl. B29f 3/10 US. Cl. 264-171 6 Claims ABSTRACT OF THE DISCLOSURE Self-crimping composite fibers of acrylonitrile polymer components, all of the same aerylonitrile polymer but some of which contain finely dispersed silica particles to reduce shrinkage thereof and the rest of which contain water-insoluble plasticizer, e.g., organic phosphate or phosphite to increase shrinkage thereof on exposure to heat so crimp is developable at elevated temperature. Such fibers are made by preparing a plurality of polymer solutions of the same polymer and the same polymer concentration, dispersing finely divided silica particles in some but not all these polymer solutions, dispersing a water-insoluble liquid plasticizer in the rest of the polymer solutions, and spinning such spinning solutions to form composite fibers by a process which includes the steps of stretching the fibers and subsequently relaxing the fibers at elevated temperature in a free-to-shrink condition to develop crimpiness therein.

This invention relates to novel self-crimping synthetic fibers of acrylonitrile polymer and to a method for producing them.

It is well known and in widespread commercial practice to manufacture fibers from acrylonitrile polymers by various spinning processes. While these various processes have numerous differences, they all have certain features in common. In all these processes, the acryloni' trile polymer is dissolved in a solvent to form a spin dope which is extruded through spinnerette orifices to form an extrudate which is then coagulated or solidified to form fibers. In these processes, the fibers are stretched to orient the molecules therein and thereafter relaxed to ease molecular strains accompanied by shrinkage of the fibers. Depending on the particular process being employed, additional steps may be involved, such as incorporating additives in the spin dope, washing the fibers, drying the fibers, restretching the relaxed fibers, applying finishes, cutting to form staple fibers, etc.

The products resulting from these processes as described above are substantially straight fibers. Natural fibers, such as wool and cotton, have many desirable properties due to their crimpiness. It was early recognized that these fibers of acrylonitrile polymer would be better suited for many uses if they were made crimpy.

One general approach which has long been in commercial use is to mechanically crimp these fibers of acrylonitrile polymer. Several specific techniques have evolved. In gear crimping, the fibers are passed through the nip of a pair of coacting gears. In stuffer crimping, the fibers are compacted or stuffed into a confined zone or stuffing box under pressure. In twist crimping, the fibers are tightly twisted and then untwisted. In all of these processes, crimp is imparted to the fibers by the application of mechanical forces to the fibers, usually at elevated temperature. Because of well-recognized deficiencies of the products of these processes, such as physical damage to the fibers caused by the crimping apparatus and loss of crimpiness during textile processing due to stresses and heat, a second general approach has found commercial favor in recent years.

A second general approach which was first invented about 1942 and which has found significant commercial "United States Patent 3,798,296 Patented Mar. 19, 1974 use since about 1960 is to produce composite fibers whose components shrink by different amounts when exposed to identical conditions. In this process, two or more distinct spinning solutions are simultaneously extruded through each orifice of a spinnerette to form a composite extrudate which is then coagulated or solidified to form composite fibers. Thereafter, these composite fibers are processed by steps which include, in the case of composite fibers of acrylonitrile polymer, stretching to orient the molecules therein and thereafter relaxing to ease molecular strains accompanied by shrinkage and crimping of the fibers. Depending on the particular process being employed, additional steps may be involved, such as those mentioned above for producing regular acrylonitrile polymer fibers.

Several types of composite fibers, differing in the physical disposition of the components thereof, are known. In side-by-side composite fibers, the components are disposed alongside each other along the length of the fiber, as illustrated and described in Kulp et al. US. Pat. 2,386,173; Sisson et al. US. Pat. 2,428,046; Ryan et al. US. Pat. 2,988,420; and Fujita et al. US. Pat. 3,182,106. In sheath-core composite fibers, the components are disposed one within and completely surrounded by another throughout the fiber length, as illustrated' and described in Breen US. Pat. 2,987,797; Breen US. Pat. 3,038,236, FIGS. 8, 12, and 13; Fukuma et al. US. Pat. 3,500,498; and Ueda et al. US. Pat. 3,541,198. In random composite fibers, the components are randomly disposed within and adjacent each other, as illustrated and described in Miller US. Pat. 2,805,465; Baer US. Pat. 3,182,352; Powell et al. US. Pat. 3,295,552; and Matsui et al. US. Pat. 3,613,173. In each of these composite configurations, one component shrinks more than another during some treatment, usually by heat in an unrestrained state, to develop coily crimp. The present invention relates to an improvement in this technology of producing composite fibers of acrylonitrile polymers and is particularly related to producing the difference in shrinkage behavior needed for crimp formation.

In the production of composite fibers, it is important that the components adhere to each other and not split apart during the expected life of the products made therefrom, which requires that the components be compatible.

It is also important that all the components be spinnable using some common spinning conditions since they must all be spun simultaneously through each spinnerette orifice. It is also important, as noted above, that the components shrink by difierent amounts when subjected to some treatment, such as exposure to heat in a relaxed, free-to-shrink condition. Commercially, this treatment is preferably exposure to steam, hot water, or heated air since the materials used are inexpensive, non-polluting, and easily removed from the fibers.

The most widely used technique is to select similar polymers of difiering chemical composition for each component, as exemplified in Fujita et al. US. Pat. 3,182,106 where the polymers comprise the same monomers but in different proportions, or Calhoun US. Pat. 3,006,028 where the components were a homopolymer and a copolymer of acrylonitrile. Each polymer must be separately made and separately dissolved to form separate spinning solutions which necessarily involves duplication of facilities and increased costs. In order to avoid some of these disadvantages (viz, those associated with requiring a plurality of different polymers), it has been proposed to use one polymer but to prepare a plurality of spinning solutions of different concentrations therefrom, as in Dawson et al. US. Pat. 3,084,993. The amount of differential shrinkage obtainable by this method is very small and only a limited amount of crimpiness is obtainable. This 3 process, moreover, still requires the duplication of dissolving and solution handling with the attendant increased costs. The present invention relates to improving this technology still further so as to achieve high differences in shrinkage while using only a single polymer and only a single spinning solution to substantially eliminate the necessity for duplication of facilities and reduce costs.

In accordance with the present invention, composite fibers of acrylonitrile polymer are prepared wherein each component thereof is the identical polymer and wherein the necessary shrinkage difference results from the inclusion of finely dispersed silica in at least one but less than all the components and the inclusion of a waterinsoluble liquid plasticizer for acrylonitrile polymers in the rest of the components. Preferably, this is accomplished by preparing one acrylonitrile polymer and dissolving it in a solvent to form a spinning solution. Just prior to extrusion, this solution is subdivided into a plurality of streams and finely divided silica is mixed into one or more streams, but not into all streams, and the water-insoluble liquid plasticizer is mixed into the remaining streams, and the separate streams are spun together using any of the apparatus for spinning composite fibers, such as those depicted in the various patents cited above. The methods chosen for mixing the silica and the waterinsoluble liquid plasticizer are not critical as long as the silica and the plasticizer are finely dispersed in the respective acrylonitrile polymer solutions.

The acrylonitrile polymers useful for the practice of this invention should contain at least about 70% polymerized acrylonitrile and up to 30% ethylenically unsaturated comonomers polymerizable therewith. Numerous such comonomers are known, such as those disclosed in U.S. Pats. 2,874,446; 2,948,581; 3,222,118; and the various other patents referred to therein. Any of the usual solvents for acrylonitrile polymers can be used to prepare solutions thereof, such as the organic solvents, e.g. dimethylformamide, dimethylacetamide, ethylene carbonate, and aqueous salt solvents, e.g. those disclosed in U.S. Pats. 2,140,- 921; 2,558,730; and 2,648,647 although other solvents may be used provided they are inert to the silica and the water-insoluble liquid plasticizer to be dispersed therein. The spinning solutions can be spun into fibers using the wet, dry, and air-gap spinning procedures well known in the art. It is only necessary that such procedure include a stretching step to orient the acrylonitrile polymer molecules in the fibers and thereafter a relaxating step to ease the molecular strains to permit shrinkage and crimp development, as is usual in processes for making composite fibers of acrylonitrile polymers.

The silica particles useful for the practice of the present invention are commercially available products which characteristically are of extremely small particle size, e.g., less than about 300 angstrom units; have a large surface area, e.g., greater than about 100 square meters per gram; and contain surface reactive hydroxyl groups. Among such silica products are the fumed silicas, such as Aerosil sold by Degussa Inc. and Cab-O-Sil sold by Cabot Corp., and the colloidal silicas, such as Ludox sold by Du Pont, Nalcoag sold by Nalco Chemical Co., and Nyacol sold by Nyacol Inc. Further descriptions of some of these silicas can be found in Pruett U.S. Pat. 3,156,666 and Precopio et a1. U.S. Pat. 2,888,424 and the various technical bulletins of the aforesaid vendors of these products. In such bulletins, Aerosil fumed silica is described as produced by flame hydrolysis of silicon tetrachloride in the gas phase at 1100 C. and Ludox colloidal silica is described as produced by the teachings of Bechtold et al. U.S. Pat. 2,574,902 and Rule U.S. Pat. 2,577,485. These silica products are widely known, having found numerous applications in diverse industries. I

Any water-insoluble liquid plasticizer for acrylonitrile polymers may be used for the practice of the present invention. Especially preferred are the water-insoluble liquid organic phosphates and phosphites having the formulae:

wherein R R and R are each selected from alkyl of 3 to 18 carbon atoms, alkoxyalkyl of 4 to 18 carbon atoms, phenyl, and lower-alkyl-substituted phenyl, which may contain chlorine and/or bromine substituents thereon. Illustrative of such compounds are tridecyl phosphate, dipropyl-octadecyl phosphite, tricresyl phosphate, tr1- benzyl phosphate, isooctyl-diphenyl phosphite, tris[2,2 bis(propoxymethyl)butyl] phosphate, tris(2,3-dibromopropyl) phosphate, tri[2 bromo 1 (chloromethyDethyl] phosphate, tris(2,3-dichloropropyl)phosphate, tris[2- chloro-l-(chloromethyl)ethyl] phosphite, 2,4,6-tribromophenyl bis(isopropyl) phosphate, tris[2,2-bis(2,3 dibromopropoxymethyl)butyl] phosphate, dicyclohexyl-isopropyl phosphite, etc.

As pointed out above, it is known to prepare composite fibers of acrylonitrile polymer by spinning processes which include the steps of stretching the composite fibers to orient the molecules therein and relaxing the previously stretched composite fibers to ease molecular strains accompanied by shrinkage and crimping of the fibers due to the difference in amounts of shrinkage among the components thereof. In such process, the present invention relies on the addition of silica particles to at least one but less than all the components of the composite fiber and of the water-insoluble liquid plasticizer to the remaining components to produce the shrinkage dilferential needed for crimp development during the relaxing step. Thus, the composite fibers of the present invention preferably have all components of the same acrylonitrile polymer and they are spun from acrylonitrile polymer solutions which preferably are of the same polymer concentration in the same solvent, i.e., they are identical polymer solutions differing solely in the presence of silica particles and water-insoluble liquid plasticizer separately in the various components for crimp formation. However, other additives, such as dyes, etc. may be present provided they do not affect the shrinkage characteristics of the fiber.

It is not known why the inclusion of silica particles into the acrylonitrile polymer matrix reduces the ability of the polymer component to shrink on exposure to elevated temperature, although it is believed that such particles produce a rigidity effect restricting movement of the polymer molecules. It is also not known why the inclusion of the plasticizer into the acrylonitrile polymer matrix increases the ability of the polymer component to shrink on exposure to elevated temperature, although it is believed that such liquid plasticizer enables the polymer molecules to slide past each other more easily by reducing intermolecular friction. In any case, the acrylonitrile polymer components containing such silica particles shrink less and the acrylonitrile polymer components containing such liquid plasticizer shrink more than corresponding acrylonitrile polymer components devoid of such additives at conditions causing shrinkage.

In the composite fibers of this invention, sufficient differential shrinkage to cause self-crimping during relaxation is achieved when about 2.0 to 10.0%, preferably 3.0 to 8.0, of silica particles on weight of polymer is dispersed in one component of the composite fibers and 3 to 30%, preferably 5 to 25% of the liquid plasticizer is dispersed in another component of the composite fibers. The exact amounts are not critical, but depend on the amount of crimpiness desired, the distribution and relative proportions of the polymer components, and the relaxation or shrinkage conditions. In general, it appears that there is about a one percent reduction in shrinkage for every one percent of silica included in the acrylonitrile polymer component containing silica and about a one percent increase in shrinkage for every one percent of liquid plasticizer included in the acrylonitrile polymer component containing plasticizer. Quantities in excess of about silica are normally to be avoided due to excessive thickening of the spinning solution causing problems in extruding such viscous solutions.

This invention will now be illustrated by the following examples depicting preferred embodiments thereof, it being understood that the invention is not limited to such embodiments.

EXAMPLE 1 A large quantity of a spinning solution containing 9.9 percent of a copolymer of 81% acrylonitrile, 10% vinylidene chloride, and 9% methyl methacrylate, 46.0 percent sodium thiocyanate, and 44.1 percent water was prepared and divided into a plurality of portions. A silica masterbatch containing 10.53 percent silica, 42.00 percent sodium thiocyanate, and 47.47 percent water was also prepared.

Portion 1 of this spinning solution was split and flowed through two parallel flow paths, path A receiving about 60% and path B receiving about 40%. Into the spinning solution flowing in path A was continuously mixed at sufficient qu ntity of tris (2,3-dibromopropyl) phosphate to result in the spinning composition A containing 0.95% tris(2,3-dibromopropyl)phosphate well dispersed therein. Into the spinning solution flowing in path B was continuously mixed 2. sufficient quantity of the silica masterbatch to result in spinning composition B containing 0.51% silica well dispersed therein. These two spinning compositions A and B were then flowed through a static mixer to provide slight random mixing of the two spinning compositions. The two randomly mixed spinning compositions were then extruded together through a spinnerette into a cold (about 3 C.) dilute (13.5% salt concentration) aqueous sodium thiocyanate coagulant to form wet gel filaments which were, in sequence, stretched in air at room temperature to 2.5 times their unstretched length, washed wih water to remove residual sodium thiocyanate, stretched another 4 times (to a total of 10 times the un stretched length) in water at 99 C., and dried in a relaxed condition in a humid atmosphere at 127 C. dry bulb and 6 and about 2.7% silica on total weight of fiber). After processing this staple fiber into yarn (2 ply s Philadelphia count) on conventional textile equipment and immersing the yarn in boiling water, the crimpiness was redeveloped, and the yarn had a specific bulk of 7.7 cubic centimeters per gram.

In a control run in which all conditions were the same as above except the tris(2,3-dibromopropyl) phosphate and silica were omitted, no crimp developed during the steam relaxation step and the yarn, after immersion in boiling water, had a specific bulk of only 3.5 cubic centimeters per gram.

EXAMPLES 2-4 Portions 2, 3, and 4 were each split into two parts, each part admixed with tris(2,3-dibromopropyl) phosphate or silica masterbatch, the two parts were slightly random mixed in a static mixer, spun into fibers, and converted to yarn using the same process as in Example 1 except that the concentrations of tris(2,3-di'bromopropyl) phosphate and silica added were varied.

For instance, in Example 2, sufficient tris(2,3-dibromopropyl) phosphate was admixed into the split in path A to result in the spinning composition A containing 1.48% tris(2,3-dibromopropyl) phosphate well dispersed therein and sufiicient silica masterbatch was admixed into the 40% split in path B to result in the spinning composition B containing 0.92% silica well dispersed therein. After spinning, etc., as in Example 1, analysis of the staple fibers indicated that the A component contained about 13.2% tris(2,3-dibromopropyl) phosphate and the B component contained about 9.7% silica (for an overall analysis of about 7.9% phosphate and about 3.9% silica on total weight of fiber). Total shrinkage due to the drying and steam-relaxing steps was 39% of the stretched length and considerable crimpiness developed. After immersing the yarn made from the straightened and mechanically crimped fibers in boiling water, the crimpiness redeveloped and the yarn had a specific bulk of 8.9 cubic centimeters per gram.

In a similar manner, in Examples 3 and 4, other concentrations of these same additives were utilized to produce fibers. The results of these tests, along with the results of the tests of Examples 1, 2, and the control run 69 C. wet bulb for 15 minutes (as taught by Robertson 45 (without additives), are reported in the following table.

TABLE Analysis of fibers, percent Phosphate, Silica 1n Phos- Percent Yarn Compocompo phate in Silica in total bulk Example nent A nent B fiber fiber shrinkage emi /gm.

Control 0 0 0 0 40 8.5 10.3 6.7 6.2 2.7 43.5 7.7 13.2 9.7 7.9 3.9 39.0 8.9 24.7 7.2 14.8 2.9 45.2 10.3 25.8 6.0 15.5 2.4 43.3 9.3

et al. US. Pat. 2,984,912) to collapse the fiber structure. During this drying step, the fibers shrank about 20% of their stretched length, an amount not sufficient to cause crimp development. The dried filaments were then exposed to steam at 125 C. for 60 seconds in a relaxed free-toshrink condition, during which the filaments shrank additionally to a total shrinkage of 43.5% of their stretched length and considerable crimpiness developed. The filaments were then restretched slightly (enough to straighten out the crimpiness) in Water at 88 C. and then quenched in water at 70 C. while under tension to yield straightened filaments. These straightened filaments were then mechanically crimped at 80 C. to give two to six crimps per inch, dried at C., and cut into staple fibers averaging 16.65 denier. Analysis of these fibers indicated that the A component contained about 10.3% tris(2,3-dibromopropyl) phosphate and the B component contained about 6.7% silica (for an overall analysis of about 6.2% phosphate In a similar manner, crimpy composite fibers of acrylonitrile polymer can be prepared using spinnerette assemblies which produce side-by-side or sheath-core composite fibers. Also, other water-insoluble liquid plasticizers can be used in lieu of the specific phosphate illustrated in the foregoing examples without departing from the teachings of this invention.

I claim:

1. In the process of spinning composite fibers of acrylonitrile polymer by simultaneously extruding through each orifice of a spinnerette a plurality of acrylonitrile polymer solutions, which process includes the steps of stretching the fibers and subsequently relaxing the fibers at elevated temperature in a free-to-shrink condition, the improvement comprising preparing a plurality of acrylonitrile polymer spinning solutions of the same polymer and the same polymer concentration and dispersing (a) finely divided silica particles in at least one but less than all said polymer solutions and (b) a waterinsoluble liquid plasticizer for acrylonitrile polymers in the rest of said polymer solutions prior to extrusion, said fibers developing crimp during said relaxing step due to the presence of the finely divided silica and the plasticizer in separate polymer components of the resulting composite fiber.

2. A process as defined in claim 1 wherein said relaxing is by exposure to steam.

3. A process as defined in claim 1 wherein said silica has a particle size of less than about 300 angstrom units, a surface area greater than about 100 square meters per gram, and surface reactive hydroxyl groups.

4. A process as defined in claim 1 wherein 2.0 to 10.0% on weight of polymer of silica is dispersed in each acrylonitrile polymer solution containing same.

5. A process as defined in claim 1 wherein said waterinsoluble liquid plasticizer is a water-insoluble liquid organic phosphate or phosphite having the formula:

wherein R R and R are each selected from the group of moieties consisting of alkyl of 3 to 18 carbon atoms,

alkoxyalkyl of 4 to 18 carbon atoms, phenyl, and loweralkyl-substituted phenyl, and such moieties containing chlorine or bromine substituents thereon.

6. A process as defined in claim 1 wherein 3 to on weight of polymer of plasticizer is dispersed in each acrylonitrile polymer solution containing same.

References Cited UNITED STATES PATENTS JAY H. WOO, Primary Examiner US. Cl. X.R.

26029.6 AN, 29.6 AG, 29.6 MP, 30.6 R, 41 R, 41 C; 264168, 182, 211