CA1102944A - Formation of polymeric fibers by a seeding technique - Google Patents

Abstract

ABSTRACT
Polymeric fibers are formed from solution by the influence of polymeric seeding materials under circumstances which do not otherwise yield polymeric fibers.

Description

RELATED AP LICATION
In Canadian application Serial No. 277,864, filed May 6, 1977, by L. Brian Keller and Robert K~ Jenkins, new compositions of matter resulting from a novel fiber formation process were disclosed. Attempts to utilize the technology of the above applicatlon to produce polymer fibers from many soluble polymers disclosed by the present invention failed.
The present invention describes a method for extending the processing techniques of the prior application to new classes of polymeric fibers.

BACKGROUND OF THE INVEM~ION
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1. Field of the Invention Thls invention relates to the preparation of polymeric fibers in general and to the formation of fibers from solu~ion in particular.

2. Prior Art The formation of fibers from polymeric materials by spinning from a melt or from a highly viscous solution is old. These methods involve the initial formation of the fiber by a mechanical step such as extrusion through a spinnerette or drawing a fine continuous thread from the viscous melt. In the case of formation from the molten material the fibers are cooled and subseauently stretched and heat treated to develop desired mechanical pxoperties. In fibers spun from highly concentrated solvent solutlons the solvent is removed by evaporation or extraction following the spinning step. They are then mechanlcally stretched and heat treated in the same manner as fibers formed from the meltO

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In recent years, the formation of fibers by stirring very dilute solutions of certain polymers has been described in the scientific literature, Pennings, A. J., Vander ~lack, et al. (Pol~mere, 99 (1969)). Thls procedure results in the formation of linear fibers attached to the stirrer. The fibers are non-uniformly distributed around the stirrer and are spirally arranged. The formation of similar fibers from stirred solutions has also been reported by A. Keller (Physics Today, May 1970, page ~2). In addition, a crystalline material of fibrous shape having what is described as a "shish-kebab" structure has been formed by irradiating a dilute solution of polyethylene in p-xylene with ultrasonics at 0.1 - 4 mW/cm rrom 85 to 190 Kilo HZ at a temperature of between 82 and ~8C. The concentration of polyethylene in the solvent ranged rom 0.05 to 0.5~ by weight and the fibers formed were sparse and very short (Blackadder and Schleinetz, Nature 200, 778, 1953).
Applicants herein disclose a process for generating unique masses o~ fibers rom solutions of certain polymers by agitating the solutions at sonic frequencies. (Canadian application 277,864). The fiber masses so formed consist of coharent, interconnected three dimensional arrayed networks o very fine ibers. The method of forming fiber ~asses by sonic agitation of a cooling polymer solution was found to be useful with linear organic polymers, having a regularly repeated chain structure and a degree of crystallinity as determined by x-ray di~fraction. The class of polymers described as polyalkenes are particularly amenable to fiber formation by the sonic agitation procedure. In general, isotactic polypropylene most readily formed fibers under these -- 3 ~

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conditions and mixtures of isotactic-polypropylene and other poly-alkenes form fiber masses more readlly than the poly-alkenes alone. Non-crystalline polymers do not readily form fibers from solutions by the nrocess disclosed ln application Serial No. 277,864.
The ability to form dense fibrous masses from solution is highly desirable, particularly if the solute is a curable polymer or a curable polymer may be infiltrated into the mass ater it is formed. This capabilit~ would facilitate the fabrication of superior solid encapsulants for complex geometry electrical devices.
Applicants know of no prior art processes for preparing fibers, fiber masses and fiber reinforced composites wherein the fibers are formed from solution in a manner which facilitates the fabrication of self-reinforced insulating elements within intricate electrical components. -T~E INVENTION
Summary In seeking to provide a method for prepari.ng reinforcing fibers for use in composite material compositions serving as insulation in intricate electrical components, applicants have invented a process for forming a variety of polymeric fibers from solution. This process may be used to induce the formation of fikers from solutions of linear polymers which are essentially atactic and not highly crystal-line.
The improved process for precipitating fibers from a polymeric solution, comprises: providing a solution of a non-crystalline polymer in a heated solvent; adding a linear : 30 isotactic crystalllne polyalkene to said solution thereby .~

forming a hot mixed polymer solution; and subjecting said mixed solution to mechanical or sonic vibration, while simultaneously lowering the temperature of said mi~ed solution to precipitate polymeric fibers there~rom. Preferably said non-crystalline polymer is a linear organic polymer, such as an acrylonitrile-butadiene-styrene terpolymer or a tetra-fluoroethylene-hexafluoropropylene-vinylidene terpolymer.
Also preferably said crystalline polyalkene is polypropylene or polyethylene.

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In our previous wor~ we observed (Application Serial No. 277,864) that ~ibers and fiber masses can be produced by sonic agitation of more concentrated polymer solutions while cooling. Furthermore, we observed that useful composites can be produced by forming the fibers and fiber masses from solution in a curable polymer or by secondary impregnation of the fibers and fiber masses with a curable resin. Fibers and riber masses were prepared ~rom polyethylene and from a variety of polyalkene polymers providing that the polymers possessed a high degree of crystallinity. Composites prepared from these fiber masses were shown to exhibit good mechanical properties, thermal resistanca and dimensional stability on aging.
All of the previous work however, was limited to the class of polymers de~ined as linear polyal~enes whlch have uniform symmetrical structures and are highly crystalline.
Only one exception was noted in our previous work. Nylon 6, a noncrystalline atactic polymer, was observed to form ~ibers in combination with isotactic, highly crystalline polypropylene.
Th.is behavior was attributed to the pronounced tendency o~
nylons to ~orm fibers because of the strong hydrogen bonding be-tween the molecules of this c].ass of polymers.

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We have discovered a new method of growing fibers and fibrous masses from polymeric material that employs a seeding concept. Utilizing our method it is possible to prepare fibers and fiber masses by stirring and other means of agitation from polymers that will not form fibers from solution by any known technique. The fiber masses and composites possess significant advantages over comparable prior art products.
Fiber forming materials which are useful in this invention are linear, organic polymers~ The seed materials are high molecular weight organic polymers, having-a regularly repeated chain structure and a high degree of crystallinity as determined by ~-ray diffraction. The crystalllne polymer, isotactic polypropylene, is particularly useful as a seeding polymer. ~e have successfully used our seeding invention to produce fibers and fiber masses consisting essentially of poly-(acrylonitrile butadiene styrene~; a terpolymer of ethylene, propylene and acrylic acid3; isotactic 4-methyl-l-pentene and several other polymeric materials. Generally, the seed polymer used in the above fiber mass formations was isotactic poly-propylene of highmolecular weight ~average viscosity of ~00~,0003; however, other seeding materials such as polyethylene and polymers ~aken from the group of isotactic, crystalline polyalkenes will also function as seeding polymers.
A solution of the seed polymer and of the polymer which dses not normally form fibers by this method is formed.
The solution will preferably cGntain about 2% to 20~ by weight of 1 ~he fiber forming and seed material, the upper limit being 2 dic~ated by the limit of solubility of the fiber formed.

3 The ratio of seed polymer to fiber forming polymer may vary

4 from 1% to 90~ oP the weight polym~rs in the solution.
The choice of solvents will depend upon various factors 6 such as the nature of the solute and the final product to be 7 obtained from the process. When nne wants to isolate the 8 fiber mass, then the solvents generally are in the xylene 9 and toluene class of alkylbenzenes.
In general, it is necessary to heat the solvent in 11 order to dissolve an adequate amount of the fiber forming 12 and seed material therein. Temperatures ranging from 110 1~ to 140~C are adequate. The solution is then allowed to 14 cool slowly while it is simultaneously subjected to a high stirring rate which in turn creates an intense velocity 16 gradient between the stirring rod and container or to some 17 other form of vigorous agitation, either mechanically or 18 vibrationally inducedl At some temperature range durin~
19 the cooling and agitation, dependent upon the concentration, type of polymers, and solvPnts, an abundance of fibers will .
21 appear.

22 Fibers produced by stirring are usually attached to 23 and spirally arranged around the stirrer. In the event that 24 the cooling polymer solution is ~ubjected to agitation by vlbration in the sonic range, dense interconnected fibrous 26~ networks are formed. Ihese networks we have generally 27 ~ ~referred to as fiber masse Other methods of agi~ation 28 also produce fibers, ~or instance the submersion of an : :
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1 object in a cooling polymer solution while the object is 2 shaken, vibrated, or subjected to a reciprocating motion 3 of frequencies in the sonic range will cause fibers to 4 be formed upon and attach to the object.
If the fiber mass is the desired product, the solvent ~ may be removed by routine methods, the precise method being 7 dictated by the nature of the solvent. For instance, a 8 volatile solvent may be removed by simple evaporation. A
~ relatively nonvolatile solvent can be washed out with a volatile liquid, the traces of which can then he evaporated.
11 The resultant fibers or fibrous mass may then be impregnated 12 with a curable resin to form a composite material having 13 excellent physical, chemical and thermal resistance 14 characteristics.
' 15 Our fibers and fiber masses have a ~ariety of prac-16 tical uses. They may be used in the formation of papers, 17 cloth, felts~ mats~ nonwoven fabrics, cordage and the l1ke.
18 In addition, the masses may be broken up to provide indi-19 vidual fibers or fiber bundles which can also be used to form paper, felts, and slmilar products. They are useful 21 in the formation of fiber-reinforced molded or cas~-products 22 While it is possible to cause fibers to form from 23 solutions having as little as ~% o~ the seeding polymer in 24 solution with the target polymer, we found that seeding polymer concentrations of from 25 to 35% by weight to yield 26 the best resul~s insofar as our particular requirements for 27 fiber ma~se~ were concernedO

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1 Our studies further indicate that the concentrations 2 of seeding material needed is dependent upon its molecul~r 3 weight distribution. It is apparent that a small fraction 4 of the higher molecular weight components of the seeding polymer initiate the ~ormation of fibers, which in turn cause 6 lower molecular weiqht components to come out as fibers along 7 with fibers from the target polymer. l~his pinciple tends 8 to suggest a seeding polymer selected from a very narrow 9 high-molecular weight range to minimize the amount of seeding material required to initiate the formation of the 11 desired polymeric mass.
12 Followlng are examples of this invention when applied 13 to fiber forming polymers which either do not form, or form 14 only with difficulty, fibers from solution by previous methods. These polymers however do meet ~he previous 16 criteria of isotacticity and crystallinity.
17 Example I.
18 0~70g of isotactic poly(4-methylpentene-1) with 0.30g 19 of isotactic polypropylene was placed into 15 ml. of styrene.
I~he mixture was heated to 130 - 140 C to effect dissolution 21 of the polymer~. The solution was csoled while under high-22 speed stirring prodacing an abundance of fibers with a blue 23 cast.
24 ~ Example II.
; 0~70g of isotactic poly~4-methylpentene-1~, 0.15g of 26 isotactic polypropylene and O.lSg of~isotactic polybutene 27 ~ were dissolved ln i5 ml. o~ styrene at 140 C. ~he solution ~28 ~ was slowly cooled under vigorou~ stirring thus producing ~a l~rge~3mount of loo~ fibers.

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Example III.
0.70g of isotactic polystyrene, lot ~911-3, and 0.30g of isotactic polypropylene were disolved into 15 ml. of styrene inhibited with benzoquinone at about 140C. The solution was cooled with good stirring to produce fibers.
Example IV.
To 30 ml. of styrene inhibited with benzoquinone was added 1.4g of isotactic 4-methyl-1-pentene and 0.60g of polypropylene. The mixture was dissolved at 135C then slowly cooled with good stirring. A large amount of fibrous mat was obtained, washed in acetone and dried.
The fibers formed on the stirring rod and in the soluent may be dispersed in a liquid using a high speed mixer or blender and separated by filtration.
The same systems as described in the examples may also be prepared as fiber masses by subjecting the cooling solution of polymers to low frequency vibrations.
~hile the examples above disclose our invention as it is applyied to the formation of isotactic poly(4 methyl-pentene-l) and isotactic polys~yrene fibers, our polymeric seeding technique may be applied to form fibers from atactic, noncrystalline polymers as well. From our studies it can be concluded that a great number of soluble linear polymers can - be casued to form fibers from a solution in which a seeding polymer has been added.
The determining factors in the selection of a seeding polymer appear to be a high degree of crystallinity, iso-tacticit~ or regular symmetrical structure and solubility in the same solvents as the flber former. Following are , .

1 examples of our invention applied to noncrystalline atactic polymers.
3 Example V.
4 To 40 ml. of xylene was added 0.28g of high molecular weight, isotactic polypropylene and 2.52g of a terpolymer 6 consisting of acrylonitrile, butadiene and styrene. The 7 mixture was heated to about 125C to dissolve both polymers 8 then slowly cooled with rapid stirring to cause the formation - 9 of layers of fiber mats. The fiber mats were washed in methyl alcohol and dried.
11 Example VI.
12 To 40 ml. of styrene with 0.45g benzoquinone to 500 ml.
13 of styrene added as an inhibitor~ was added 3.8g of XPA-l 14 (a copolymer of propylene and acrylic acid) and 0.29 of poly-propylene as the polymer seed. The mixt~re was heated to 16 140~C to dissolve the polymers then slowly cooled under rapid 17 stirring to about 30C. The fiber mats were washed in acetone 18 and dried.
19 Example VII.
2~ Two grams of ABS (acrylonitric butadiene, styrene ter-21 polymer) resin and 2g of polypropylene were added to 40 mld 22 ~ of xylene. The mixture was heated to 120C to efect dissolu-~3 ~ tion, then with stirring slow1y`cooled to room temperature.
2~ The resulting fiber masses were washed with isopropyl a~cohol ahd dried.
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26 ~ Example VIII.
~7 ~ 50/50 w/w blend o highly crystalline polyvinylidene 28 1uoride and tetrafluorethy:lene hexafluoropropylene vinylidene ~,~,1,/// //_ , ,, . .

1 fluoride terpolymer was dissolved in a solvent system to a 2 10% w/vol concentration. The solvent system consisted of 3 a 57~ 2 butanone, 15% acetone, 25~ methyl isobutyl ketone, 4 2% cyclohexanone, and 1~ diacetone alcohol mixture. A small amount non solvent~ water, was slowly introduced to the 6 polymer solutions while subjecting them to vigorous agitation 7 at ambient temperature. This resulted in the formation of 8 homogeneous fiber masses.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved process for precipitating fibers from a polymeric solution, comprising:
providing a solution of a non-crystalline polymer in a heated solvent;
adding a linear isotactic crystalline polyalkene to said solution thereby forming a hot mixed polymer solution;
and subjecting said mixed solution to mechanical or sonic vibration, while simultaneously lowering the temperature of said mixed solution to precipitate polymeric fibers thereform.

2. A process according to claim 1, wherein said non-crystalline polymer is a linear organic polymer.

3. A process according to claim 1, wherein said crystalline polyalkene is polypropylene or polyethylene.

4. A process according to claim 1, wherein said non-crystalline polymer is an acrylonitrile-butadiene-styrene terpolymer or a tetrafluoroethylene-hexafluoropropylene-vinylidene terpolymer.