CA1284858C

CA1284858C - Nonlinear carbonaceuous fiber having a spring-like structural configuration and methods of manufacture

Info

Publication number: CA1284858C
Application number: CA000506941A
Authority: CA
Inventors: Francis Patrick Mccullough, Jr.; David Michael Hall
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1985-04-18
Filing date: 1986-04-17
Publication date: 1991-06-18
Anticipated expiration: 2008-06-18
Also published as: JPH0327122A; BR8606634A; AU590879B2; DE3686504D1; EP0199567B1; DE3686504T2; EP0199567A3; JPH0327121A; JPH0670286B2; EP0199567A2; AU5635986A; KR890000129B1; JPH0327123A; JPS62500600A; WO1986006110A1; JPH0663137B2; KR880700109A; JPH0663138B2

Abstract

ABSTRACT

The present invention resides in a partially carbonized or substantially completely carbonized nonlinear resilient fiber having a spring-like structural configuration and a reversible deflection of greater than 1.2:1 and to a process of making the fiber.
In the process, the fiber is prepared from an acrylic precursor material which is stabilized and then heat treated to a temperature sufficient to impart a spring-like structural configuration on the fiber. Optionally, the precursor fiber is stabilized, collected into a fiber tow, knitted or woven into a cloth and heat treated. The cloth can then be deknitted and carded, garnetted or otherwise mechanically disassembled to produce a resilient web-like fluff or wool-like material having a considerable loft due to the spring-like structural configuration of the fibers. Electrical conductivity can be imparted to the fibers by carbonization of the fibers at a temperature of greater than 1000°C and up to 3000°C.

Description

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A NONLINEAR CARBONACEOUS FIBER HAVING A SPRING-LIKE
STRUCTURAL CONFIGURATION AND METHODS OF MANUFACTURE

The invention resides in a carbonaceous resilient fiber or fiber assembly derived from a stabilized polymeric precursor material having imparted thereto a spring-like structural configuration capable of reversible deflection of greater than about 1.2 times the length of the fiber when in a relaxed conditionO
The carbonaceous fiber of the present invention is provided with a substantially permanent, nonlinear~
resilient, elongatable, spring-like structural configuration, e.g. of a substantially coil-like, sinusoidal or other multi-curvilinear configuration having no sharp or acute angular bends in the fiber.
The spring-like structural configuration and the resilient, elongatable characteristics of the fiber allows for a dimensional change of the fiber from a relaxed condition (i.e. spring-like configuration) to an elongated, stretched, and substantially linear state, or any degree there-in-between, in which the fiber is under tension. When placed under tension~ the fiber can be extended to at least 1.2 times~ typically from 2 to 4 times, the length of the fiber in its relaxed, nondeflected, spring-like configuration. The 33,595B-F -1-~ .

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spring-like fiber can thus be deflected (elongated or stre-tched) to a substantially linear shape or configuration. If the modulus of elasticity of the fiber per se is not approached or exceeded, that is to say the fiber is not put under tension beyond that necessary to straighten the fiber to a substantially linear shape, the fiber is capable of returning from the linear to its relaxed spring-like shape over many cycles of stress elongation and relaxation without either breaking or substantially altering the dimensions or physical structure of the fiber.
The prior art has generally taught the manufacture of filaments from pitch based (petroleum and/or coal tar) compositions by the conventional techni~ue of melt spinning the composition into continuous filaments which can then be stabilized by oxidation. Such filaments are taught to be useful per se. Alternatively~ the continuous filament may be chopped, or stretch-broken into what the art refers to a a "staple" fiber. Such "staple" fiber can be converted into a yarn by drafting, drawing and twisting (referred to as spinning in the industry). The continuous filaments can also be made into a tow formed from a plurality of continuous monofilaments. The resulting yarn or threads are used per se or may be woven into cloth-like articles and used as such~ Alternatively, a woven article may be carbonized to produce a graphite or graphite-like cloth. In addition, a tow per se, may be carbonized, without weaving the tow into a cloth~ and thereafter used as reinforcement material for synthetic resinous materlals e.g. "pre--preg", and the like.
In a somewhat similar manner it has been taught that polyacrylonitrile (PAN) can be wet spun into 33,595B-F -2-filaments; the filaments assembled into a filament tow;
the filaments or tow stabilized by oxidation; the filaments or two made into staple by chopping or stretch breaking; the staple spun into yarn; the yarn knitted or woven into a cloth or fabric and, if desired, the resulting fabric carbonized at a temperature of greater than 1400C. These materials, in their pre-carbonized woven state, have been used as a noncombustible reinforcing material for metallized fire fighting suits.
In their unwoven carboni~ed form, these materials have also been used as a reinforcement material for synthetic resinous materials such as golf club shafts, and the like.
In preparing uncarbonized conventional polymeric textile yarns for knitting, weaving or other textile manufacture it is the usual practice in the industry to pinch crimp a fiber tow and thus sharply crimp-set the individual fibers of the tow (placing sharp or acute angular bends into the fiber). Such textile treatment has the same effect if used on a stabilized polymeric precursor yarn, i.e. severe and sharp angular crimps are imparted to the yarn causing entanglement among the individual fibers of the yarn and thus assisting in maintaining or fixing the short staple fibers in the yarn as well as imparting bulk properties to the yarn. However, when the procedure for the manufacture of ordinary textile yarn is followed and a yarn made from a polymeric precursor material is crimped and then carbonized, usually at a temperature above about 1000C and, more practically, at a temperature of 1400C and above, the resulting carbonized yarn becomes very brittle. That is to say, the yarn cannot be harshly handled or sharply creased, e.g. knitted or 33,595B-F -3-woven unless the knitting or weaving is done with great care and under highly controlled processing conditions.
By the same token, such a knitted or woven yarn cannot be readily deknitted, garnetted, or carded without breaking the fibers in the yarn into small segments. As a result of such brittleness, a knitted fabric cannot be deknitted without special care and such a deknitted yarn cannot thereafter be carded to convert the fibers in the yarn into a wool-like fluffy material without causing severe destruction, i.e. breakage, of the fibers. The resulting short and broken fibers do not have sufficient length or crimp to produce a well entangled fluff.
The prior art also generally discloses carbonized filaments having a high tensile strength or a high surface area. Such filaments are of a highly "graphitic" nature and necessitate the utilization of high temperatures to obtain a high degree of carbonization. However, the filaments produced by such a high temperature treatment are very brittle and incapable of standing up to stress such as a repeated bending of the filaments, particularly when they have been subjected to a temperature above about 1000C, and more so when they have been subjected to a temperature of above about 1400C. Exemplary of a high temperature treatment of filaments derived from stabilized mesophase pitch can be found in U.S. Patent No. 4,005,183 where the oxidation stabilized (at a temperature of from 250C
to 400C) fibers are made into a yarn having a low (below normal absorptive carbon) surface area and a Young's modulus within the range of from 1 to 55 million psi (7 GPa to 380 GPa).
Another technique for making a fabric panel is described in U.S. Patent No~ 4,341,830 in which a tow 33,595B-F -4-L~

of acrylic filaments is oxidized under tension, at a temperature of from 200C to 300C, crimped in a stuffer box (thus imparting a pinch type crimp), made into staple fibers, spun into a yarn which is then knitted into a cloth panel and heat treated, i.e. carbonized, in an inert atmosphere at a temperature of 1400C. The so carbonized cloth panels are assembled into a stack and the stack placed into a carbon vapor furnace for deposition of carbon onto and into the stack. This treatment is carried out by passing a carbonaceous gas, i.e. methane, through the stack while inductively heatiny the stack to a temperature of 2000C to cause carbon to be deposited onto and into the stack and thus produce a carbonaceous body having a matrix of the knitted panels. ~owever, the yarn made by this process has been found, by Comparative Example A, to be very brittle and cannot be subjected to repeated acute angular stress bending, such as would occur if the cloth panel were deknitted and carded, without severe breakage of the fibers.

GB-A-1190269 (corresponding to FR-A-1539755) discloses carbonizing a woven cloth of oxidized PAN or other polymeric fiber filament yarn. In a woven cloth the fibers are essentially linear and do not have a spring-like configuration (as defined above). There is no reference to disassembling the carbonized cloth into fibers except for extraction of fibers to test their physical properties.
U.S. Patent No. 4t423,675 discloses a carbon spring obtained by carboni~ing a length of organic linear material in the form of a coiled spring.
Specified organic linear materials include pitches and PAN. The material usually is extruded to a diameter of 33,595B-F -5-~ 3~

at least 100 micrometers and it appears to be essential that the coil is maintained under tension whilst being carbonized.
JP-A-44-2512 discloses the carbonation of Ishimeuchi or Admishiroushi woven cord or cloth formed from organic fiber yarn and subsequent removal of the warp fiber yarn to leave a resilient article. The resilience in said article arises from the arrangement of the constituent fiber yarns and not from the resilience of the fibers themselves. The fiber yarns have essentially linear portions between sharp return angle bends and hence the fibers do not have a spring-like configuration (as defined above~. There is no reference to disassembling the resilient article into fibers.
JP-A-53-98423 discloses the formation of carbon fiber elements for use in incandescent lamps by carbonizing a coil of polymer fibers and subsequently graphitizing the set fiber coil. The coil is maintained under tension during carbonization and said carbonization is conducted at a temperature of at least 150~C. The coil can be formed of a monofilament or a plurality, e.g. 400 to 1003, of monofilaments twisted together or formed into a cord.
U.S. Patent No. 4,193,252 (corresponding to 3P-A-55-40885) discloses a method of producing carbon or graphite yarn from a fabric of knitted precursor yarn by carbonization, firing and graphitization of the yarn.
The fabric can be deknitted after carbonization or firing and the deknitted yarn subjected to the subsequent heating step(s). Reference is made to use of twisted multi-ply yarn of the deknitted fibers obtained 33,595B-F -6-85~3 from the fired or graphitized fabric being of use as packing cecause of its resilience. The only exemplified precursor material is rayon and there is no reference to the carbonization of monofilaments or tows.
The present invention particularly resides in a partially carbonized or substantially completely carbonized nonlinear fiber derived from a stabilized precursor material, said fiber having a spring-like structural configuration and a reversible deflection ratio of greater than 1.2:1.
The invention also resides in a mechanical fiber spring derived from a stabilized precursor material, said fiber spring comprising a partially carbonized or substantially completely carbonized fiber having the ability to repeatedly deflect under load, either by elongation or compression of the spring structure and having the ability to recover its initial shape configuration when unloaded, said fiber spring having a dia~eter of from 4 to 20 micrometers and a reversible deflection ratio of greater than 1.2:1.
~ he invention further resides in a wool-lik,e fluff comprising an entangled mass of a multiplicity of substantially continuous nonlinear fibers, as herein-before defined.
Additionally, the invention resides in a method of forming a partially carbonized or substantially completely carbonized fiber, with reversible deflection, from a stabilized precursor material, comprising the steps of imparting a spring-like shape to the stabilized fiber, heating the fiber having said spring-like shape in a relaxed state under non-oxidizing conditions to 33,595B-F -7-~8~

impart a temporary setting of a spring-like structural configuration to the fiber, and heating the fiber having said spring-like shape in a relaxed state to impart a permanent setting of a spring-like structural configuration to the fiber.
The invention further resides in a method of forming a partially carbonized or substantially completely carbonized fiber having a spring-like structural configuration from a stabilized precursor fiber, assembling a multiplicity of the precursor fibers into a fiber tow, imparting a spring-like structural configuration to the stabilized fiber tow by knitting the fiber tow into a cloth, heating the cloth in a non-oxidizing atmosphere to a temperature of from 150C to550C to impart a temporary setting to the fibers in the cloth, deknitting the cloth, and heating the deknitted fibers to a temperature of from 550C to 1550C to impart a permanent setting to the spring-like configuration of the fibers , said carbonaceous fibers having a diameter of from 4 to 20 micrometers and a reversible deflection ratio of greater than l.2:l.
The invention additionally resides in a method of forming a wool-like fluff from a fibrous stabilized precursor material, comprising the steps of assembling a multiplicity of the stabilized fibers into a ~iber tow, imparting a spring-like structural configuration to the fiber tow by knitting the fiber tow into a cloth, heating the cloth in a non-oxidizing atmosphere to a temperature of from 150C to less than 550C to lmpart a temporary setting to the fibers in the cloth, deknitting the cloth, and mechanically separating the fiber tows in 33,595B-F -8-s~

the cloth to form said wool-like fluff of an entangled mass of fibers.
Definitions The term "fiber" or "filament" interchangeably refers to a fine threadlike body or structure of a natural or synthetic material in the conventional usage.
Included herein are filaments made by melt spinning a pitch based composition such as petroleum or coal tar, or fibers which are made by wet spinning a synthetic resinous material such as polyacrylonitrile.
The term "fiber assembly" as used herein refers to a multiplicity of filaments commonly referred to in the textile industry as a tow. Fiber assemblies are made of common polymeric textile fibers or filaments, but are also applicable to carbonaceous fibers or filaments which have been stabilized and treated in accordance with the following teaching and examples.
The term "spring-like", or "spring-like structure", or "spring-like structural configuration"
are interchangeably used herein to designate a fiber or tow that is physically deformed from a substantially linear configuration into a coil-like, sinusoidal, or other multi-curvilinear form or configuration having no acute angular bends.
The term "tow" herein refers to an assembly of 3 a plurality of continuous filaments in which the number of filaments are identified by the designation nK
wherein n is a numerical value in increments of lO00 filaments.

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--1 o_ The term "staple" refers to noncontinuous fibers which may be "spun" yarnsO
The term "stabilized" herein applies to fibers or tows which have been oxidized or otherwise stabilized against thermoplasticity to prevent them from fusing during heat setting and carbonization, at a specific temperature, typically less than about 250C for PAN
fibers, provided it is understood that in some instances the fibers are oxidized by chemical oxidants at lower temperature5.
The term "yarn" herein applies to a continuous strand of twisted fibers. The term "spun yarn" refers to a continuous strand of staple fibers which have been drated, drawn and twisted into a yarn.
The term "carding" herein refers to a procedure in which fibers are combed or brushed with a toothed apparatus, e.g. a wire brush, to effect at least a partial alignment of the staple fibers into an entangled web or sliver.
The term "garnetted" herein refers to a process for reducing ~arious textile waste materials to ~iber by passing them through a machine called a garnett, which is ~imilar to a card.
The term "knitting' herein includes single Jersey knit, Rib knit, Pearl knit, Interlock knit, 3 Double knit, and similar methods of knitting a fiber, yarn or tow into a cloth.
The term "reversible deflection" or "working deflection" is used herein as it applied to a helical or sinusoidal compression spring to mean the extent, 33,595B-F -10-5~
$~693-3798 expressed as a ratio of extendecl to free spring length to which a spring can repeateclly be extended and, on release of the extending force, return to its original (i.e. free) leng~h. Particular reference is made to the publication, "Mechanical Design - Theory and Practice," MacMillan Publ. Co., 1975, pp 719 to 748;
particularly Section 14-2, pages 721-2~.
"Hooke's law" herein refers to the stress applied to stretch or compress a body which is proportional to the strain or alternation in length so provided, as long as the limit of elasticity is not exceeded.
Polymeric precursor starting materials which have the capability of formin~ the spring-like structural configuration carbonaceous fiber of the invention are selected from starting materials such as pitch (petroleum or coal tar), polyacetylene, polyacrylonitrile (PANOX or GRAFIL), polyphenylene, polyvinylidene chloride (PVDC), and the like. GRAFIL and PANOX are Trade Marks.
Preferred precursor materials are preparad by melt spinning or wet spinning in a manner to yield a mono-filament or multi-filament assembly. The filaments are stabilized and then converted into a tow, or a woven cloth or knitted cloth by any of a number of commercially available techniques.
In accordance with the present lnvention a unique article is prepared from such a polymeric precursor material which is made into a carbonaceous fiber or two of fibers by stabilizing the fiber or tow and then providing it with a spring-like structural configuration, imparting ~o the ~iber or tow flexible, resilient, elongatable and deflectable characteristics, without ,, 3~5~
6~693-379 altering the spring-like conf:iyuration of the fiber over many cycles of elongation and contraction. Fibers made from PAN are generally oxidation stabilized at a temperature o~ from 200 C to 250C and typically have a nominal diameter of from 10 to 20 micrometers. Fibers made from mesophase pitches are oxidation stabilized at a temperature of from 250C to 400C, preferabl~ at a temperature of from 300C to 390C, as described in U.S. Patent No. 4,005,183. Fibers made from PVDC are stabilizecl by dehydrochlorination in which the fibers lose their thermoplastic nature and begin to take on a thermoset-like behavior. It will be understood that fibers having a somewhat larger diameter of, for example, 30 micrometers may be employed where stiffer fiber~ are desired, depending on the particular end use to which such heavier and stiffer fibers are to be applied.
A multiplicity of continuous fibers are associated into a tow which is then stabilized by oxidation in conventional manner. The stabilized tow is thereafter, and in accordance with the present invention, formed into a coil-like structural configuration as, for example, by winding the tow on a cylindrical rod or mandrel, or is formed into a sinusoidal form or other multi-curvilinear form by knitting the tow into a fabric or cIoth (recognizing that other fabric formlng and coll formlng methods can be employed). It ls convenient to form the sinusoidal structure on a standard textlle knittlng machine (e.g. flat bed knitting machine, or a tubular knittiny machine) or in a rounded tooth gear-box that will not ~ 5 impart any sharp or acute angular bends to the fibers.
The coil-like or sinusoidally shaped fiber, tow or the knitted cloth is thereafter heat treated in a relaxed state at a temperature of from 150C to 1550C. At a temperature of above about 250C, the fiber, tow or cloth is heat treated in an inert atmosphere. If the desired end product requires subsequent mechanical treatment, i.e., carding or deknitting of the fabric, it is preferable to subject the fiber, tow or cloth to a temperature below about 550C in an inert atmosphere.
At a temperature of from 150C to 550C, the fibers are provided with a temporary set and have not yet acquired the high degree of brittleness associated with "graphite" fibers. However~ when the fibers are initially treated in the upper range of temperatures of from 550C to 1550C, the fibers are, ab initio, provided with a permanent set. Such permanent set is accompanied by some degree of brittleness which can lead to breakage of some fibers during subsequent treatment of the fibers.
It is especially critical that, if a spring-like configuration is imparted to the fiber or fiber tow by a rounded gear tooth crimp or by wrapping around a rod or mandrel, the fiber not be heated to a temperature above about 275C, while under tension. Above this temperature, the fiber begins to lose weight and shrink in coil~ diameter and the tension resulting from such shrinkage and weight loss causes non-annealable stress cracks and weak points in the fiber.
It is, of course, to be understood that the fiber or tow may be initially heat treated at the higher temperature range up to 1550C so long as the heat 33,595B-F -13-~ 2~ 5 treatment is conducted while the fiber is in a relaxed state ~spring-like configuration) and under an inert, non-oxidizing atmosphere. As a result of the higher temperature treatment, a permanent set spring-like structural configuration is imparted to the fiber. The resulting fibers or tow having such spring-like structural configuration may be used per se, or in the case of a knitted cloth, may be deknitted to form a sinusoidal or other multi-curvilinear tow. In either event the tow or the cloth per se may then be further subjected to a carding or garnetting operation or any of a number of other methods of mechanical treatment known in the art to create an entangled wool-like fluffy material in which the fibers are separated into an entangled mass of fibers and in which the individual fibers retain their spring-like configuration.
For certain applications, it is preferred that the fibers of the inventlon have a density of less than 2.5 gm/cm3 and/or a Young's modulus of from 7 to 3B0 GPa.
The fibers, tow or the knitted cloth or the wool-like fluff produced by a heat treatment at a temperature of no higher than about 550C, in a relaxed state (which has placed a temporary set spring-like configuration into the fibers, to~ or thread) may then be further heat treated in a relaxed state and under a non-oxidizing atmosphere to a temperature of from 550C
3 to 1500C to impart a permanent set, spring-like structural configuration to the fiber. At a temperature above 1550C and up to about 3000Cv various lower degrees of electrical resistivity are imparted to the fibers, such resistivity being preferably less than about 101 ohm-cm. In the case o~ PAN fibers, the 33,595B-F -14-B5~

diameter of the fibers is reduced when treated at a higher temperature up to about 1550C. Although such higher temperature treatment results in a gradually increasing brittleness, the fibers still retain their spring-like configuration. The precursor materials are of a nature believed to lose their non-carbon moieties upon heating and form a conjugated bond structure within the carbon to carbon backbones which are believed to convert to an aromatic, fused, ring-like form.
With careful handling and with improved handling techniques, brittle fibers produced at the higher temperatures of above 1000C may still be useful as, for example, a structural reinfo~cement material for various synthetic resinous materials, as a filler material for rendering synthetic resinous materials antistatic, as electrical conductors (e.g. automobile ignition systems), as a thermal insulating material, or the like.
The stabilized fibers or tow, when heat-set into the desired spring-like structural configuration, e.g. by knitting, and thereafter heating in a relaxed state at a temperature of from 550C to 1550~C retain their re~ilient and reversible, deflectable characteristics in accordance with ~ooke's law. If the tow has been knitted and heat treated in a relaxed state at a temperature between 550C and 1000C to "perm-set"
the spring-like configuration in the tow, it may then be 3 deknitted, carded, garnetted or otherwise mechanically treated to convert the deknitted tow to an entangled wool-like fluffy material which still retains a resilience similar to that found in wool.

33,595B-F -15-, ,.

A predetermined length of fiber or tow made into a spring-like structural configuration in accordance with the above described manner will exhibit a reversible deflection in excess of 1.2 times, generally greater than twice, of its relaxed, nonelongated, spring-like configuration. Stated another way, a fiber or tow which has been provided with a permanently set spring-like configuration can be stretched or elongated to a length of at least l.2 times of its coiled, i.e. contracted, relaxed spring-like structural configuration length. By controlling the structural configuration, e.g. by controlling the knitting parameters such as the number of loops per unit length or the number of turns on a rod or mandrel, it is of course understood that a greater extension or elongation of the spring-like fiber or tow is possible.
The tightness or looseness of the nonlinear, coil or curl in the fiber, e.g. the loops per centimeter in a knitted cloth, therefor governs the extent of the 2Q elongation of the spring-like fiber or tow. Thusf the reversible deflection could be much greater than twice the length of a fiber or tow when in a relaxed state, spring-like configuration.
In a preferred embodiment, an assembly, ~.g. a bundle of fibers is obtained, by spinning a polymeric precursor material into a fiber, stabilizing the fiber, assembling a multiplicity of monofilaments or fibers into a tow, and knitting the tow into a cloth. After knitting, the fibers in the cloth are "set", i.e.
temporarily formed into a coil-like or sinusoidal structure, by treating the knitted cloth at a temperature of from 150C to 550C. Preferably ,the fibers in the knitted cloth are formed into a 33,595B-F -16-permanently set spring like structure a a temperature of from 550C to 1550C and, most preferablyr at a temperature of less than 1000C, under an inert atmosphere and in a relaxed condition. The fibers in the knitted cloth may then be carbonized at a temperature in excess of 1000C to impart other desirable properties into the fibers, as noted hereinabove.
Likewise, if a wool-like fluff is desired, the fiber tow having the spring-like configuration, or even the knitted fabric, may be carded, garnetted, or otherwise mechanically treated either before or after treatment at a temperature of less than 1550C, preferably less than 1000C, and most preferably at a temperature below about 650C, when preparing a wool-like, fluffy material. If a higher electrical conductivity in a fiber is desired, the perm set (550C
to lO00C) fiber, tow or cloth can be further heat treated to a temperature above 1000C, e.g. up to 300C.
As previously noted, fibers treated at a temperature above l550C become extremely brittle and do not readily lend themselves to a deknitting, carding or garnetting treatment. Accordingly, such carding and/or garnetting treatment should be accomplished prior to heat treatment to temperatures up to 1550C for continuous fiber or fiber tows.
Carbonaceous fibers made from polymeric 3 precursor materials normally have a surface area of from 0.5 to lÇ00 m2/gm, preferably less than 15 m2/gm when produced according to the procedures set forth above.
However~ it is known that such fibers can have imparted to them a surface area of greater than this by rapidly heating the fibers to a high temperature thereby 33,595B-F -17-converting the non-carbon moieties to gases which, on leaving the fiber, disrupt the surface. Other techniques known in the art for producing high surface area, high porosity fibers include oxidation of the fiber surface. Such high porosity fibers can be prepared from the materials of the present invention by the same techniques after the spring-like structural configuration has been imparted into the fibers.
It is also to be understood that after formation of the spring-like structural configuration into the fiber, the continuous fibers or tows may be chopped into discrete lengths and made into nonwoven products employing present day techniques for preparing such nonwoven products.
Exemplary of the products which can be produced by the technique of the present invention are set forth in the following examples:
Example l An oxidation (at a temperature of about 250C) stabilized polyacrylonitrile PANOX (R.K. Textiles) continuous 3K or 6K tow (i.e. 3000 or ~000 fibers per tow) having nominal single fiber diameters of 12 micrometers, was knitted on a flat bed knitting machine into a cloth having from 3 to 4 loops per centimeter.
Portion~ of this cloth were heat set at the temperatures set forth in Table I over a 6 hour period, under an inert atmosphere of nitrogen. When the cloth was deknitted, it produced a tow which had an elongation or reversible deflection ratio of yreater than 2:l. The deknitted tow was cut into various length of from 5 to 25 cm, and fed into a Platts Shirley (Trade Mark) 33,595B-F -18-_19_ Analyzer. The fibers of the tow were separated by a carding treatment into a wool-like fluff, that is to say, the resulting product resembled an entangled wool-like mass or fluff in which the fibers had a high interstitial spacing and a high degree of interlocking as a result of the coiled and spring-like configuration of the fibers. The fiber lengths of each such treatment were measured and the results of these measurements set forth in Table I.

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Example 2 A fabric was knitted from a 3K or 6K PANOX
(R.K. Textiles) continuous stabilized filament tow on a Singer flat bed knitting machine and heat treated at the temperatures set forth in Table II and under an inert atmosphere of nitrogen. The fabric was then deknitted and the tow having a spring-like structural configuration fed directly into a carding machine. The resulting wool-like mass was collected onto a rotating drum and had sufficient integrity to enable it to be easily handled. The length of the fibers ranged from 2 to 15 cm. The wool-like mass treated at a temperature of 950C was highly conductive and had a resistance of less than 75 ohms at any probe length taken at widely separated distances up to 60 cm in the wool-like mass.

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Example 3 A 3K PANOX stabilized tow was knitted on a Singer flat bed knitting machine at a rate of 4 stitches/cm and was then heat treated at a temperature of 950C, under an inert atmosphere of nitrogen. The cloth was deknitted and the tow (which had a coil elongation or reversible deflection ratio of greater than 2:1) cut into 7.5 cm lengths. The cut yarn was then carded on a Platt Miniature Carding machine to produce wool-like fluff having fibers ranging from 3.5 to 6.5 cm in length with an average length of about 5 cm. The wool-like fluff had a high electrical conductivity over any length of up to 60 cm tested.

Example 4 In a similar manner to Example 3 a portion from the same knitted cloth was heat treated at a temperature of 1550C and under an inert atmosphere of nitrogen.
The cloth itself and the deknitted tow had a very high electrical conductivity. On carding 15 cm lengths of cut tow, a fluff was obtained which had fibers of lengths of from 2.5 to 9.5 cm with average lengths of 5 cm. Thus, carding of a deknitted, continuous filament to~, fabric which had been subjected to a temperature of above 1000C is still capable of producing a wool~ e fluffy product.
Comparative Example A
A staple 2 ply singles 10's stabilized polyacrylonitrile PANOX yarn was knitted into a tubular sock at a rate of 4 loops per cm and thereafter heat treated at a temperature of 1550C under an inert atmosphere of nitrogen. The yarn was then cut into 10 33,595B-F -23-348r,~3 cm lengths. The cut yarn was then carded in a carding machine. The resulting product was collected with difficulty. Only short fibers having a length of from 0.5 to 1.25 cm were obtained along with a high level of dust. The difficulty of fiber recovery resulted from the high degree of twist and fiber entanglement which is typically found in spun yarns. Similar result~ were obtained when this example was repeated, starting with a similar spun yarn sample of GRAFIL-01 obtained from Hysol-Grafil Ltd., Coventry, England.
Example 5 A series of runs were made to determine the effect various heat treatment temperatures had on the fibers. A significant property was the specific resistivity of the fibers. To determine such property, numerous samples of an oxidation stabilized polyacrylonitrile yarn having a density of from 1.35 to 1.38 g/cm3 was assembled into 3K and 6K tows. The tows (identified as PANOX and manufactured by R.K. Textiles of Heaton-Norris, Stockport~ England), were knitted into a plain jersey flat cloth having from 3 to 4 stitches per cm, respectively. The cloth was thereafter heat treated at various temperatures under an oxygen free nitrogen pad in an incremental heat control quartz tube furnace. The temperature of the furnace was gradually increased from room temperature to about 550C over a three hour period with the higher temperatures being 3 achieved by 50C increments every 10-15 minutes. The material was held at the desired temperature for about 1 hour, the furnace opened and allowed to cool while purging with nitrogen. Representative of the furnace temperatures at the above preset incremental temperature 33,595B-F -24--3~
-~25-schedule is that for a 6K yarn and shown in ~able III
following:
TABLE I I I
Time Temp. C

0~20 300 0935 ~20 2~ 1035 650 10~5 700 The specific resistivity of the fibers was calculated from measurements made on each sample using a measured average of 5i~ measurements, one made from fibers removed at each corner of the sample and one made from fibers removed from each edge, approximately at the middle of the sample. The results are set forth in Table IV following:

33,595B-F -25-TABLE IV
Log Flnal Specific Temp. in C % Wt. Loss Resistivity 500 - ~.849 600 2.~10 700 - _ 750 37 -1.21 850 38 -2.02 goo 42 -2.54 ~50 ~5 -2.~4 1000 48 -3.026 1800 51 -3.295 The carbonized and permanently et fibers of the invention, when treated at temperatures sufficiently high to render the fibers electrically conductive and yet sufficiently low where the fibers still exhibit resilient, flexible, and nonbrittle characteristics, are particularly suitable for blending with standard carpet fibers or yarn to produce a yarn having static dissipation properties. Such a carpet/yarn blend may incorporate at least 0.25 weight percent carbonized fibers in the carpet yarn. The weight ratio of synthetic carpet fibers to carbonized fibers is preferably greater than 100:1 to 200:1~ A carpet employing the carbonized fibers of the invention exhibited static discharge properties to 0 percent of an applied electrostatic charge in less than 1 second.

33,595B-F -26-I

:

E~ample 6 Monsanto 1879 nylon (trilobal) staple was blended with 0.5 percent by weight of a conductive fiber prepared in accordance with the present invention. The conductive fiber was prepared by heating an oxidatively stabilized polyacrylonitrile multifilament fiber tow which had been knitted into a cloth, heat treated at about 1500C, deknitted and cut into staple approximately 18 cm in length. The blended staple was carded and the resulting sliver was pin drafted three times, recombination ratios were lO:l, 3:1, and 5:1, respectively. The resulting drafted sliver was spun into a single ply yarn with an average twist of about 4.75. The majority of the carbonaceous fiber was broken into lengths much smaller than the original 18 cm lengths, resulting in a large loss of carbonaceous fiber from that originally included in the singles spinning process. The resulting carbonaceous fiber containing singles yarn was plied with a nylon yarn made in the same fashion but containing no carbonaceous fiber. The 3.00/2 ply yarn which was heat set on a Suessen (Trade Mark) heat setting apparatus was thereafter tufted into a 1/8 inch (3 mm) gauge, 27.03 on (765 gm), 9.5 mm pile height carpet (a cut loop form) with approximately 3 stitches per cm. The ratio of carbonaceous fiber to yarn containing no carbonaceous yarn in the tufting operation was 1:5, respectively. A portiun of the carpet was backed with a commercial nonconductive latex carpet backing. The resulting carpet was tested for static di~charge properties by charging the carpet to 5000 volts while in an atmosphere having a relative humidity of less than 20 percent. The static charge was dissipated to 0 percent of original charge in less than 33,595B-F -27-,, ~28-one second, and some of the samples discharged in less than 1/2 second. The standard or the industry is a discharge to 0 percent in 2 seconds or less.
This example illustrates that temperatures above about 1000C can be employed in heat-setting the spring-like structural configuration into the ~arbonaceous fiber tow, but that at temperatures above 1000C much embrittlement occurs and the fibers resulting were inefficiently used, being lost as short fibers and not incorporated into the yarn when drafted with normal carpet staple to prepare singles.
Example 7 In another example lO0 grams of the same precursor acrylonitrile fiber tow as described in Example 6 was used. However, the precursor fiber was heat treated after knitting at a temperature of 950C.
All other aspects of handling the carbonaceous material were the same. The carbonized fiber was blended with 45 kg of the Monsanto 1879 nylon yarn as in Example 6. The resulting yarn contained 0.02 percent carbonized fibers which were substantially evenly distributed throughout the yarn. The yarn was tufted to prepare a carpet in a similar manner to Example 6. Thus, each tufted end has the carbonized fibers. Results were similar to the results obtained in Example 6.
Knitted yarn or fiber tows which have been heat treated to a temperature above 1000C, and thus been rendered electrically conductive, have also found special utility in the manufacture of electrodes for a non-aqueous secondary energy storage device such as described in Canadian Patent No. 1232941 issued on 33,595B-F -28-February 16, 1988, entitled "Energy Storage Device" by F. P. McCullough, Jr. and A. F. Beale, Jr~
ExamPle 8 In another experiment, tows made by deknitting a flat stock cloth in which the tow was a stabilized polyacrylonitrile precursor of the indicated filament count which had been heat-set at the indicated temperatures prior to deknitting. Tow lengths were measured for resilient deflection by adding known weights to the tow portion and the intermediate and the final deformations as well as the final nonresilient elongation deflection measured. The results are set forth in Table V.

33,595B-F -29-8~
~30-TABLE V

Sample Description: a b c d e f g h Heat Treat.
in C.: 650 650 650650 170 300 5251550 950 ~ .
Relaxed Length (mm) 106 92 122 107 137 145109 63 77 Weight Added (gm) DEFLECTION (mm) O O O O O O O O O O
0.275 16 33 25 31 38 55 51 22 29 0.901 54 101 75 71 69 111 13157 81 1.526 83 140 87 98 66 116 167~2 108 2.10799 163 116 105 66 115187 94 119 2.468 110 172 128 115 61 116 196104 126 2.943 119 186 133 119 60 118 201114 132 Stretched:; 216 256 208 187 98 157249 185 276 Relaxed~ ' 0 6 1 0 49 25 14 0 0 33,595B-F -30-, : , ~1 i .

~3 .~~

Sample (a) Panox 6K tow with 0.4 twists/cm as plain jersey with 3-4 picks/cm.
~b) Panox 3K -tow with no twist, plain jersey knit with 4-5 picks/cm.
(c) Grafil-O1, 6K tow with no twist knitted as Interlock with 3 picks/cm.
(d) Grafil-Ol knitted as interlock with 3 picks/cm.
(e) Panox 6K tow with 0.4 twists/cm knitted as plain jersey with 3-4 picks/cm.
(f) Panox 6K tow wi-th 0.4 twists/cm knitted as plain jersey with 3-4 picks/cm.
(g) Panox 6K tow with 0.4 twists/cm, knitted as plain jersey with 3-4 picks/cm.

5 (h & i) PANOX 3K tow with no twist, plain jersey knit with 4-5 picks/cm.
* Fully stretched to structure length ** All load removed coil returns to relaxed state 33,595B-F -31-~4 ~5 Comparative Example B
To illustrate the effect of tension on the fibers during setting of the spring-like configuration, a 6K tow of PANOX continuous fibers was roll-wrapped onto an 8 mm quartz rod. The wound tow was heat treated according to the schedule as set forth in Example 5, Table III to a final temperature of 300C while holding the ends of the wrapped tow secure. The heat treatment set a spring-like configuration into the tow. However, the fibers were very stiff and the tow was removed from the rod with difficulty. Many of the fibers broke on removal. This tow did not have the same resilience as tows which had been heat set in a relaxed knitted configuration. If the same procedure is employed but the spring-like tow is heated to a temperature of 350C, much greater breakage occurs even before removal.
The latter procedure was repeated and the heat treated material (350C~ after being carefully removed from the rod was heated while in a relaxed state slowly to a temperature of about 650C to determine whether any annealing would occur. None did. The resultant coil was brittle and had no resiliency.
However, if the wrapped coiled tow was removed from the rod prior to reaching 275C and a smaller diameter rod inserted to maintain the integrity of the spring-like shaper heating in this "relaxed" state resulted in a spring-like tow having substantially the same properties as the aforedescribed deknitted tows.

33,595B-F -32-

Claims

1. A partially carbonized or substantially completely carbonized nonlinear fiber derived from a stabilized precursor material, said fiber having a diameter of from 4 to 20 micrometers, a spring-like structural configuration and a reversible deflection ratio of greater than 1.2:1.

2. The fiber of Claim 1, wherein said carbonaceous fiber has a diameter of from 4 to 20 micrometers and a reversible deflection ratio is greater than 2:1.

3. The fiber of Claim 1 or 2, wherein said fiber has a specific electrical resistivity of less than 1010 ohm-cm.

4. The fiber of Claim 1, wherein said fiber has a density of less than 2.5 gm/cm3, and a Young's modulus of from 7 GPa to 380 GPa.

5. The fiber of Claim 1, wherein said fiber has a surface area of from 0.5 to 1600, m2/gm.

6. The fiber of Claim 5, wherein said fiber has a surface area of from 0.5 to 15 m2/gm.

33,595B-F -33-

7. The fiber of Claim 1, wherein said carbonaceous precursor material is a polymer or copolymer of polyacrylonitrile

8. The fiber of Claim 1, wherein the log specific resistivity of said carbonized fiber is greater than -2.84.

9. A mechanical fiber spring derived from a stabilized precursor material, said fiber spring comprising a partially carbonized or substantially completely carbonized fiber having the ability to repeatedly deflect under load, either by elongation or compression of the spring structure and having the ability to recover its initial shape configuration when unloaded, said fiber spring having a diameter of from 4 to 20 micrometers and a reversible deflection ratio of greater than 1.2:1.

10. The fiber spring of Claim 9, wherein said precursor material is a polymer or copolymer of polyacrylonitrile.

11. A wool-like fluff comprising an entangled mass of a multiplicity of partially carbonized or substantially completely carbonized fibers as claimed in Claim 1.

12. The wool-like fluff of Claim 11, having a resistance of less than 75 ohms at a probe distance of about 60 cm when measured across the wool-like fluff.

13. The wool-like fluff of Claim 11 or 12, wherein said polymeric precursor material is a polymer or copolymer of polyacrylonitrile.

33,595B-F -34-

14. A method of forming a partially carbonized or substantially completely carbonized fiber, with reversible deflection, from a stabilized precursor material, comprising the steps of imparting a spring-like shape to the stabilized fiber, heating the fiber having said spring-like shape in a relaxed state under non-oxidizing conditions to impart a temporary setting of a spring-like structural configuration to the fiber, and heating the fiber having said spring-like shape in a relaxed state to impart a permanent setting of a spring-like structural configuration to the fiber.

15. The method of Claim 14, wherein said stabilized fiber is heated to a temperature of from 150°C to 550°C to impart said temporary setting of a spring-like configuration to the fiber.

16. The method of Claim 14, wherein said stabilized fiber is heated to a temperature of from 550°C to 1550°C to impart said permanent setting of a spring-like configuration to the fiber.

17. The method of Claim 14, including the step of assembling a multiplicity of stabilized fibers into a fiber tow, imparting said spring-like structural configuration to the fiber tow, and heating the fiber tow in said relaxed condition to a temperature of from 550°C to 1550°C to impart said permanent setting to the fiber tow.

18. The method of Claim 16 or 17, including the step of heating the permanently set fiber in a non-oxidizing atmosphere at a temperature of up to 3000°C to render the fiber electrically conductive.

33,595B-F -35-

19. The method of Claim 17, including the step of imparting said spring-like configuration to the stabilized fiber tow by winding the tow around a cylindrical rod or mandrel, heating the wound fiber tow to a temperature of from 150°C to less than 300°C in a non-oxidizing atmosphere, unwinding the fiber tow from the cylindrical rod or mandrel, and then heating the fiber tow, in said relaxed condition, and in an inert atmosphere, to a temperature of from 550°C to 1550°C to form a partially carbonized or substantially completely carbonized fiber tow having said reversible deflection.

20. The method of Claim 17, including the step of imparting said spring-like configuration to the stabilized fiber tow by knitting the tow into a cloth, heating the cloth to a temperature of from 150°C to 550°C to impart said temporary setting to the fibers in the cloth, deknitting the cloth, and heating the fiber tows from the deknitted cloth to a temperature of from 550°C to 1550°C to impart a permanent setting spring-like configuration to the fiber tows.

21. The method of Claim 17, including the step of imparting said spring-like configuration to the stabilized fiber tow by knitting the tow into a cloth, heating the cloth to a temperature of from 150°C to 550°C, deknitting the cloth, and mechanically treating the deknitted fiber tow to form a wool-like fluff.

22. The method of Claim 21, including the step of heating the wool-like fluff to a temperature of greater than 1000°C to render the fibers in the fluff electrically conductive.

33,595B-F -36-

23. The method of Claim 21, including the steps of deknitting the cloth, heating the fiber tow to a temperature of greater than 1000°C to render the fibers in the tow electrically conductive, and incorporating the electrically conductive fibers into a synthetic resinous material.

24. The method of Claim 14, wherein said precursor material is an acrylic fiber.

25. The method of Claim 24, wherein said fiber is a polymer or copolymer of polyacrylonitrile and has a density of less than 2.5 gm/cm3 and a Young's modulus of from 7 GPa to 380 GPa.

26. The method of Claim 14, wherein said carbonaceous fiber has a diameter of from 4 to 20 micrometers and a surface area of from 0.5 to 1600, m2/gm.

27. A method of forming a partially carbonized or substantially completely carbonized fiber having a spring-like structural configuration from a stabilized precursor fiber, assembling a multiplicity of the precursor fibers into a fiber tow, imparting a spring-like structural configuration to the stabilized fiber tow by knitting the fiber tow into a cloth, heating the cloth in a non-oxidizing atmosphere to a temperature of from 150°C to 550°C to impart a temporary setting to the fibers in the cloth, deknitting the cloth, and heating the deknitted fibers to a temperature of from 550°C to 1550°C to impart a permanent setting to the spring-like configuration of the fibers , said 33,595B-F -37-carbonaceous fibers having a diameter of from 4 to 20 micrometers and a reversible deflection ratio of greater than 1.2:1.

28. The method of Claim 27, including the step of further heating the deknitted fibers to a temperature of up to 3000°C to render the fibers electrically conductive.

29. The method of Claim 27 or 28, wherein said fiber is an acrylic.

30. The method of Claim 27, wherein said acrylic fiber is a polymer or copolymer of poly-acrylonitrile and has a density of less than 2.5 gm/cm3 and a Young's modulus of from 7 GPa to 380 GPa.

31. The method of Claim 27, wherein said fiber has a specific electrical resistivity of less than 1010 ohm-cm.

32. The method of any one of Claims 27 to 31, wherein said fiber has a surface area of from 0.5 to 1600, m2/gm.

33. A method of forming a wool-like fluff from a fibrous stabilized precursor material, comprising the steps of assembling a multiplicity of the stabilized fibers into a fiber tow, imparting a spring-like structural configuration to the fiber tow by knitting the fiber tow into a cloth, heating the cloth in a non-oxidizing atmosphere to a temperature of from 150°C to less than 550°C to impart a temporary setting to the fibers in the cloth, deknitting the cloth, and 33,595B-F -38-mechanically separating the fiber tows in the cloth to form said wool-like fluff of an entangled mass of fibers.

34. The method of Claim 33, wherein said fibers have a diameter of from 4 to 20 micrometers and a reversible deflection ratio of greater than 1.2:1.

35. The method of Claim 33, including the step of heating the wool-like fluff to a temperature of up to 3000°C to impart electrical conductivity to the wool-like fluff.

36. The method of Claim 33 or 35, including the step of incorporating the wool-like fluff into a polymeric material.

33,595B-F -39-