CA1146712A - Hollow acrylonitrile polymer fiber - Google Patents

Abstract

27,596 Title: HOLLOW ACRYLONITRILE POLYMER FIBER

ABSTRACT OF THE DISCLOSURE
Acrylonitrile polymer fiber is disclosed in which a continuous uniform hollow extends throughout the fiber length which hollow is surrounded by a solid polymer composition sub-stantially devoid of sheath-core structure, density gradient, and void structure, said fiber being of less than about 50 deniers per filament and having desirable textile properties.

Description

27,59~ 7~

This invention relates to hollow acrylonitrile poly-mer fiber having suitable denier and physical properties for textile applications. r~Ore particularly, this invention relates to such a fiber having a cross-section comprising an inner hol-low area which extends throughout the length of the fiber and a ; solid polymer area surrounding said hollow area and having a uniform structure possessing optical clarity.
Hollow fibers are desirable for a number of reasons.
Such fibers possess high bulk compared to solid fibers of the same denler and are highly desirable in the abrication of wearing apparel wherein they provide improved comfort. They also provide increase moisture adsorption, wicking, improved soil hiding qualities, and improved esthetic qualities such as touch or feel and sparkle or internal reflectance.
-15 Textile fiber of acrylonitrile polymer having hollow - cores therein have been difficult to provide. This is because such polymers when fashioned into fibers by suitable procedures do not retain the hollows induced therein throughout the fiber--making process. Prior to recent developments, acrylonitrile polymer fiber for textile applications could only be success-fully provided commercially by wet-spinning or dry-spinning pro-cedures. Using such procedures, the requirement for a polymer solvent and a liquid or gaseous coagulant rendered any procedure for hollow formation extremely difficult to perform and at best - 25 provided only small amounts of discontinuous voids within the fiber. Using other fiber-forming polymer types involving melt--spinning procedures, the necessity to maintain the nascent ex-trudate hot to effect orientation stretching and at the same time to avoid fusing of the individual sticky filaments during processing complicates processing when hollow fibers are sought.

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Recent developments in the field of acrylontrile polymer fibers have led to a melt-spinning process involving fusion melts. A fusion melt is a combination of an acrylonitrile polymer and preferably water in proportions which form a homogeneous single-phase melt. The fusion melt forms a temper-ature which is above the boiling point of water at atmospheric pressure. As a result, the melt is formed at autogenous or greater pressure to maintain water in the liquid state. The resulting melt forms at a temperature which is below the normal melting point of the polymer and safely below the deter-ioration temperature of the polymer. The melt can be extruded under condi-tions which provide a fibrous material. However, most of the melt-spinning procedures proposed do not provide an acrylonitrile polymer fiber of desirable textile properties and do not lead to the provision for a hollow acrylonitrile polymer of textile denier and properties.
There continues to exist~ therefore, the need for hollow acrylonitrile ~` polymer fibers that are of suitable denier and have desirable properties for use in textile applications. The provision for such fiber would fulfill a long-felt need and constitute a significant advance in the art.
In accordance with the present invention there is provided an acrylo-nitrile polymer fiber having a monolobal cross-sectional shape comprising (1) an inner hollow area extending uniformly throughout the entire fiber length and having a substantially fully opened cross-section and completely sur-rounding said inner hollow area (2) an outer solid polymer area having a uniform structure, said fiber being less than about 50 denier per filament and having suitable physical properties for textile uses and said acrylonitrile being a hydrophilic polymer provided by adding a pre-formed polymer selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, poly-ethylene oxide, polyacrylamide and polyacrylic acid to acrylonitrile and one or more monomers copolymerizable therewith in proportions which provide at least about 50 weight percent acrylonitrile and about 1 to 10 weight percent of hydrophilic moieties in the resulting polymer.

The fiber of the present invention in preferred embodiments is of ~ ,"
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textile denier, i.e., of a denier of less than about 20 per filament and has physical properties admirably suitable for textile applications. Such fiber, has a continuous hollow core extending uniformly throughout the iber length so that maximum benefits associated with hollow fibers can be realized.
Preferably, the hollow core constitutes about one-third or more of the total fiber cross-section. In special embodiments of the fiber of this invention multiple hollow cores may be provided in a single fiber structure.
The hollow fiber of the present invention demonstrates highly improved wicking properties over similar fiber not containing such hollow. This property coupled with the fast-drying properties of hydrophobic fibers in general leads to unexpected utility in such uses as towelling and the like.
The hollow fiber of the present invention may be provided by a melt-spinning procedure using a homogeneous single-phase fusion melt of acrylo-nitrile polymer and water following required processing steps. When these required processing steps are followed, fiber properteis are impaired and the fiber is unsuitable for many textile and other uses.
In carrying out preferred processing to provide the hollow acrylonitrile polymer fiber of the present invention, a homogeneous single-phase fusion melt of a hydrophilic fiber-forming acrylonitrile polymer and water is pre-pared in accordance with conventional procedures. This fusion mel~ is thenextruded through a spinneret assembly which provides a hollow structure such as a spinneret plate having annular orifices or a conventional spin-7~

neret plate modified with pins or suitable inserts to provi~
a fiber of hollow structure. Such extrusion is conducted in such a manner that the extrudate which is in the form of fila-ments issues directly into a steam-pressurized solidification zone maintained under conditions which prevent formation of a sheath-core structure within the solid polymer area and minimize formation of a density gradient and voids therein. ~Jhile t~e nascent extrudate remains within the steam-pressurized solidifi-cation zone, it is subjected to orientation stretching at stretch ratios adequate to provide desirable textile properties in the fiber which results following processing. Such stretching can be ~ccomplished within the steam-pressurized solidification zone because under the conditions maintained sufficient water remains within the extrudate to maintain the extrudate in the plastic state. Stretching may be accomplished in one or more stages while within the solidification zone and can lead to fine denier filaments as well as highly desirable physical properties for textile applications.
The acrylonitrile-water fusion melt when spun through a spinneret directly into a solidifying medium solidifies rapid-ly without forming sticky surfaces and retains with high con-- for~.ity the shape of the spinneret orifices without the need for any special handling such as injection of a secondary fluid to retain the hollow structure. As a result, a variety of fiber shapes and hollow configurations can be employed in producing fiber having excellent conformity and shape-forming orifices - employed including those providing hollow structures.
After the fiber has been solidified in the steam--pressurized solidification zone and stretched as described, the filaments are dried under suitable conditions of temperature and humidity to minimize or prevent void formation within the solid polymer area of the fiber. Af1:er suitable drying as indicated, it is desirable to rela~
the stretched and dTied filaments in steam to obtain a desirable balance of physical properties.
To prepare the preferred melt-spun, hollow acrylontrile polymer fiber of the present invention, a suitable acrylonitrile polymer composition is selected to form the polymer area of the fiber structure. Any acrylonitrile polymer composition having at least about 50 weight percent of acrylontrile units is suitable provided the polymer composition also has associated there-with hydrophilic moieties to provide the transparent nature of the polymerarea. There are a number of techniques by which the hydrophilic moieties can be introduced into the acrylonitrile polymer composition effectively.
One method of introducing hydrophilic units into an acrylonitrile polymer composition is to copolymerize acrylonitrile with a hydrophilic comonomer. Another method is to polymerize the acrylonitrile polymer com-position in the presence of an redox initiator system that introduces acid groups at the polymer chain ends. Yet another method is to polymerize the acrylonitrile polymer composition in the presence of a pre-formed hydro-philic polymer such as polyvinyl alcohol. Still another method is to hydrolyze a small portion of the acrylonitrile units of a pre-formed acrylonitrile polymer to provide hydrophilic acrylic acid and/or acrylamide units. Further, one can modiy a portion of the acrylonitrile units of a pre-formed acrylo-nitrile polymer by suitable reaction to provide hydrophilic groups, such as by reaction with ethylenediamine to provide imidazoline units. These and other methods known to those skilled in the art can be used alone or in com-bination to provide hydrophilic units associated ~, . ..
,~, - 5 -~1~ ~, z with the acrylonitrile polymer composition used to prepare the fiber of the present invention.
An acrylonitxile polymer composition useful to provide the fiber of the present invention may be a single polymer or a blend of compatible polymers so long as the composition provides a minimum of at least about 50 weight percent of acrylonitrile units and hydrophilic moieties associated therewith to achieve the desired transparency. Individual compatible polymers in blends need not contain the specified amounts of acrylonitrile units or hydrophilic moieties so long as the total blend compos-ition provides the required amounts of such materials. By "hydrophilic moieties" as that term is used herein are meant those portions of the acrylonitrile polymer composition that are hydrophilic and include such moieties as sulfonic acid groups, polyvinyl alcohol segments, repeating comonomer units, and the ~, like. By "associated therewith" as that term is used herein and in the appended claims is meant that such hydrophilic units are presént in the acrylonitrile polymer composition in a manner ap-propriate for the particular hydrophilic moieties involved. Thus, sulfonic acid groups may arise as end groups on polymer chains or as a functional group on a comonomer; polyvinyl alcohol moiet-ies may be present as part of a grafted polymer; other hydrophil-ic moieties may arise as repeating units in a copolymer prepared from two or more monomers or as a result of hydrolyzing a suit-able polymer; they may also arise as a result of suitable react-ion of a pre-fonned polymer; they may arise as a compatible poly-mer blend; and such other methods as are known to those skilled in the art. Thus, the term "associated therewith" is intended to include the various manners in which hydrophilic moieties are pre-sent in the acrylonitrile polymer composition since no other term-inology is appropriate to cover all of the manners describea.
The amount of hydrophilic moieties in a given acrylon-itrile polymer composition that achieves the desired transpar-ency will vary widely depending upon many factors. The content of hydrophilic moieties will be influenced by the nature of the hydrophilic groups, the molecular weight of the polymer, the content of acrylonitrile in the polymer, the nature of the poly-mer composition, i.e., copolymer, graft, blend, etc., the pre-sence or absence of more than one type of hydrophilic moieties, - l0 processing conditions and other variables. However, useful con-tents of hydrophilic moieties can readily be found by trial fol-lowing the teachings given herein as a guide.
Individual acrylonitrile polymers useful in preparing the acrylonitrile polymer composition for melt-spinning the fib-er of the present invention do not have to contain the hydrophil-ic moieties or acrylonitrile units, as indicated above, so long as the acrylonitrile polymer composition is suitably constituted to provide these components. With such contents implicit, suit-able acrylonitrile polymers include homopolymers of acrylonitrile and copolymers of acrylonitrile and one or more of the following monomers:
H~DROPHOBIC MONOMERS
- Methyl methacrylate, ethyl acrylate, butyl acrylate, metho~ymethyl acrylate, beta-chloroethyl acrylate, and the cor-responding esters of methacrylic acid and chloro-acrylie aeid;
vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chlor-ide, vinylidene bromide, allyl chloride, l-chloro-l-bromoethyl-ene; methacrylonitrile; methyl vinyl ketone; vinyl formate, vinyl acetate, vinyl propionate, vinyl stearate, vinyl benzoate;
N-vinyl phthalimide, N-vinyl succinimide; methylene malonic ;7~

esters; itaconic esters; N-vinyl carbazole; vinyl furan; alkyl vinyl ethers; diethyl citraconate, diethylmesaconate; styrene, dibromostyrene; vinyl naphthalene; 2-methyl-1-vinylimidazole, 4-methyl-1-vinylimidazole, 5-methyl-1-vinylimidazole; and the like.
HYDROPHILIC MONOMERS
Acrylic acid, methacrylic acid, alphachloroacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, p-methoxyallyl benzene sulfonic acid, acrylamidomethylpropane sulfonic acid, ethylene-a,~-dicarboxylic acids and their salts; acrylamide, methacrylamide, dimethylacryl-amide, isopropylacrylamide; allyl alcohol; 2-vinylpyridine, 4--vinylpyridine, 2-methyl-5-vinylpyridine; vinylpyrrolidone;
vinylpiperidone; 1,2-dihydroxypropylmethacrylate, hydroxyethyl methacrylate; 1-trimethylammonium-2-hydroxypropyl methacrylate methosulfate; and the like.
In preparing acrylonitrile polymers and copolymers it i5 desirable to employ redox systems such as sodium persulfate--sodium bisulfate to initiate and control the polymerization.
Such use results in sulfonic acid end groups on the polymer formed. The proportion of sulfonic acid end groups in the poly-mer will vary with molecular weight of the polymer, higher pro-- portions being present in polymers of low molecular weight.
These sulfonic acid end groups should be taken into account when determining the content of hydrophilic moieties in the acrylonit-rile polymer composition used to provide the fiber o the present invention. Acrylonitrile polymer compositions containing sulfon-ic acid groups arising solely from the use of an appropriate redox system can be effectively employed to provide the fiber of the present invention. When hydrophilic pre-formed polymers lZ
such as polyvinyl ~lcohol, polyvinyl pyrrolidone, polyethylene oxide, poly-acrylamide, polyacrylic acid, and the like are to be used to provide the acrylonitrile polymer composition, it is desirable that such pre-formed polymers be added to the monomer composition to be polymerized to provide the acrylonitrile units. Individual polymers of the composition may range in molecular weight from about 10,000 to 200,000 or more so long as the com-position provides fiber of desirable properties.
Once a desired acrylonitrile polymer composition for forming fiber has been selected, it is next desirable to prepare a single phase homogeneous fusion melt of the composition and water. A single phase fusion melt of acrylonitrile polymer composition and water results when suitable quantities of polymer composition and water are heated at elevated temperature and pressure sufficient to maintain water in liquid state. The amount of water necessary will vary depending upon the polymer composition employed. For a given polymer composition, there will be a range of water contents that will provide the single phase fusion melt at the operating temperature and pressure.
This can readily be determined from a phase diagram. Use of too low a water content or temperature will result in a separate phase of unmelted polymer.
Use of too high a water content will result in a separate phase of polymer-water melt and an added phase of free water. The fusion melt should be obtain-ed at a temperature safely below the deterioration or decomposition tempera-ture of the polymer composition. Sufficient temperature and mixing should be employed to ensure that a homogeneous fusion melt is obtained.
The fusion melt is conveniently obtained in conjunction with spinning using a screw extruder coupled with a pump and spinneret. A suitable procedure for melt extrusion is describ-ed in U. S. Patent 3,991,153, issued November 9, 1976 to G. X.
Klausner et al. Other types of melt-spinning devices may be used such as a piston extruder in conjunction with a spinneret, for example.
The fiber of the present invention may be obtained in a variety of melt-spinning procedures employing the fusion melt of acrylonitrile polymer composition and water. The fusion melt may be extruded through a spinneret into any suitable en-vironment, sabjected to orientation stretching and such other processing options as may be desired. The resulting fiber may also be subjected to such additional processing steps as may be desired.
In carrying out a preferred method for preparing the fiber of the present invention, the homogeneous single phase fusion melt of acrylonitrile polymer composition and water is ex-truded through a spinneret directly into a steam pressurized solidification zone maintained under conditions such that the nascent extrudate is solidified but is maintained in a plastic state so that the nascent extrudate may be subjected to orient-ation stretching while within the solidi~ication zone. As the stretched extrudate emerges from the solidification zone, it enters atmospheric conditions.
~fter the extrudate has emerged from the solidification zone, the extrudate is next subjected to conditioning in an oven maintained at certain conditions of temperature and humidity as reflected by dry and wet bulb temperatures. Generally the dry bulb will be in the range of about 120-180C. and the wet bulb - temperature will be in the range of about 60-100C. The time of treatment may vary widely depending upon the wet and dry bulb 7~;~

temperatures used and generally will vary from about 10 to 15 minutes. This conditioning step is conducted before any uncontrolled or tensionless shrink-age of the extrudate has occurred. This conditioning step may be conducted on the extrudate in afree-to-shrink condition or under tension.
After conducting the conditioning step as described one may conduct additional optional process steps if desired. Subsequent to the conditioning step described immediately above, certain optional processing steps may be carried out to augment the dyeing characteristics. One provision is to sub-ject the conditioned ex*rudate to dry heat at a temperature in the range of about 130-220C. for 1 to 30 minutes, the time decreasing with increasing temperature. A second provision is to subject *he conditioned extrudate to steaming such as in an autoclave.
The invention is more fully illustrated by the Examples which fGllow wherein all parts and percentages are by weight unless otherwise specified.
Figure 1 illustrates the final fiber contained in the invention.
Figure 2 is a photograph of the final fiber with ends submerged in water with dye for tracing.

A conventional spinneret plate having a plurality of orifices of 300 micron diameter was fitted with insert pins to form an annular orifice. Each pin was 1~5 micron in diameter.
An acrylonitrile polymer of the following composition was employed:
Acrylonitrile 85%
Methyl methacrylate 11.9%
Poly(vinyl alcohol) 3%
Acrylamidomethylpropanesulfonic acid 0.1%
The polymer has a kinematic molecular weight 40,000. Kinematic molecular weight (Mk) is determined from the viscosity measure~ent of a 1%
solution of the polymer in 50% sodium thiocyanate at 40C. using the formula: hk = V x 10,500, where V is the ab-solute viscosity in centipoise (after correction viscometer constant).
A mixture of 84.6 parts polymer, 15.4 parts water, and 0.25 parts of a glycol stearate type lubricant was ~ed to an extruder, melted and extruded through the hollow fiber spin-neret described above directly into a steam pressurized solidi-- fication zone maintained at 13 pounds per square inch gauge with saturated steam. The filaments were stretched at a stretch ratio of 9.2 in the first stage and 6.4 in a second stage. The resulting 6.5 d/f fiber was dried at 139C. dry bulb/7~C. wet bulb and steam relaxed at 116C. The final fiber obtained was hollow as shown in Figure 1 and had the following properties.
- - Denier per filament 9.7 Straight Tenacity 2.7 gms/denier -Straight Elongation 21~
Loop Tenacity 2.0 gms/denier Loop Elongation 18~
Figure 2 (photograph) of this hollow fiber with ends submerged in wat~r with dye for tracing shows that water wicks up the ; hollow fiber about 4 inches, while no wicking was observed in the control. The transparency of the fiber is evident from the fact that the color of the dyed water can be seen in the photo-graph (Figure 2).

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An acrylonitrile polymer fiber having a monolobal cross-sectional shape comprising (1) an inner hollow area extending uniformly throughout the entire fiber length and having a substantially fully opened cross-section and completely surrounding said inner hollow area (2) an outer solid polymer area having a uniform structure, said fiber being less than about 50 denier per filament and having suitable physical properties for textile uses and said acrylonitrile being a hydrophilic polymer provided by adding a pre-formed polymer selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, polyacrylamide and polyacrylic acid to acrylonitrile and one or more monomers copolymerizable therewith in proportions which provide at least about 50 weight percent acrylonitrile and about 1 to 10 weight percent of hydrophilic moieties in the resulting polymer.

2. The fiber of Claim 1 wherein said hollow area constitutes about one-third or more of the total fiber cross-section.

3. The fiber of Claim 1 wherein said denier is less than about 20 per filament.

4. The fiber of Claim 1 wherein said acrylonitrile polymer is a graft of acrylonitrile, methyl methacrylate and acrylamido-methylpropane sulfonic acid.

5. The fiber of Claim 1 wherein said denier is less than about 10 per filament.