CA1156409A - Method of producing carbon fiber and product thereof - Google Patents
Method of producing carbon fiber and product thereofInfo
- Publication number
- CA1156409A CA1156409A CA000376727A CA376727A CA1156409A CA 1156409 A CA1156409 A CA 1156409A CA 000376727 A CA000376727 A CA 000376727A CA 376727 A CA376727 A CA 376727A CA 1156409 A CA1156409 A CA 1156409A
- Authority
- CA
- Canada
- Prior art keywords
- fibers
- fiber
- acid
- process according
- oxidation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
- D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
- D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
- D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
- D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
Abstract
ABSTRACT OF THE DISCLOSURE
A novel process is provided for the formation of improved fibrous materials (primarily of acrylonitrile units) with increased modulus of elasticity and strength as well as decreased diameter. Preferably, the material is acrylonitrile, typically copolymerized with a minor amount of an acrylic monomer such as methyl acrylate. Oxidation of the fiber is effected at an elevated temperature in the presence of a car-boxylic acid, other than formic acid, or its anhydride within the fiber. It is believed that the acid and/or its anhydride which is formed at the oxidizing temperature serves as a plasticizer and reduces the fiber yield stress and increases fiber plasticity so that the fibers may be drawn by as much as 300% or more in the presence of the acid and/or its anhydride during oxidation, thereby providing the desired improvement in increased elasticity and strength.
A novel process is provided for the formation of improved fibrous materials (primarily of acrylonitrile units) with increased modulus of elasticity and strength as well as decreased diameter. Preferably, the material is acrylonitrile, typically copolymerized with a minor amount of an acrylic monomer such as methyl acrylate. Oxidation of the fiber is effected at an elevated temperature in the presence of a car-boxylic acid, other than formic acid, or its anhydride within the fiber. It is believed that the acid and/or its anhydride which is formed at the oxidizing temperature serves as a plasticizer and reduces the fiber yield stress and increases fiber plasticity so that the fibers may be drawn by as much as 300% or more in the presence of the acid and/or its anhydride during oxidation, thereby providing the desired improvement in increased elasticity and strength.
Description
1 15f~9 1 The present invention relates to polyacrylonitrile (PAN)
2 fibers and partic~larly improved oxidi~ed PAN fibers and the
3 carbonized and graphitiæed forms thereof.
4 Polyacrylonitrile (-C~2CM(CN)-) constitutes a major com-ponent of many industrial texti]e fihers. Oxidized PAN fiber 6 is potentially useful to form heat protective fabrics as a 7 substitute for asbestos. Carbonized and graphitiæed polyacry-8 lonitrile (PAN) fibers form composites with other materials, 9 particularly where high strength-to-density and high modulus-to-density ratios are desired. However, such applications are 11 limited by the ultimate strength, elasticity and diameter of 12 the carbonized and graphitized PAN fibers. Thus, it is not 13 surprising that many attempts have been made to increase 14 strength and elasticity and reduce the diameter of PAN fibers.
Particularly, the smaller the diameter of the fiber, the 16 greater is the ratio of surface area of the fiber to either 17 weight or volume. The greater ratio thus provides increased 18 fiber-to-matrix interface area, distributing the loading on 19 the composite over a greater area so as to improve interlami-nar shear strength markedly for composite materials utilizing 21 such smaller diameter fibers. Additionally, smaller diameter 22 fibers of improved strength and elasticity are considerably 23 more flexible than larger diameter fibers of similar strength 24 and elasticity, permitting formation of desirably thin woven fabrics or even braided and knitted fabrics, as composite pre-26 cursors.
27 Present methods for the production of PAN-based carbon 2a ~ fiber~ cal or the spinning of the PAN, followed by oxidation .
~ 11564~.'3 1 ¦ and carbonization of the resulting P~N fibeLs. ~rhe acrylo-2 ¦ nitrile monomer can be made by several known methods including 3 ¦ direct catalytic adc3ition of hydroyen cyanide to acetylene or 4 ¦ the addition of HCN to eth~lene oxide to give ethylene cyano-¦ hydrin, followed by dehydration. Polymerization is usually 6 ¦ carried out in an aqueous solution with the polymer precipi-7 ¦ tating from the system as a fine white powderO
8 ¦ Pure polyacrylonitrile is difficult to spin because it is 9 ¦ not sufficlently soluble in many organic solvents and is not 10 ¦ readily dyed. Consequently, polymers other than a pure PAN
11 ¦ homopolymer are often produced. Thus, a "PAN" fiber may 12 ¦ actually be an acrylic polymer formed primarily of recurring 13 ¦ acrylonitrile units copolymer~zed with a minor proportion of 14 ¦ methyl methacrylate, vinyl pyridine, vinyl chloride and the 15 ¦ like. Th'ese copolymers exhlbit properties substantially simi-16 ¦ lar to an acrylonitrile homopolymer~ By convention if the 17 ¦ fiber does not contain more than about 15 percent foreign 18 ¦ material it is refered to as polyacrylonitr'ile, and if more 19 ¦ than 15% then as modlfied acrylonitrile. Examples of such 20 ¦ copolymers include PAN fibers produced under trade names such 21 ¦ as Orlon* (E.I. DuPont de Nemours~, Courtelle SAF* (Courtaulds 22 ¦ Ltd.) and Acrilan (Chemstrand)~
23 ¦ The conversion o the PAN to fibers may be accomplished by 24 either dry or wet spinning. In the latter a salt solution of the polymer is extruded through a spinneret into a liquid which 26 can coagulate the PAN. In the dry spinning process a filament 27 is formed by the evaporation of a volatile solvent from a PAN
28 solution. In either case the filaments are subsequently *~trade mark 1 11564(~3 1 ¦ stretched to several times their original lenyth a~ a sliyhtl~
2 ¦ elevated temperature, for example 100C, so as to dra-" out and 3 ¦ align the m~in polymer chains and increase ln-~rchair-~dhesion. '~ur" U.S.
4 ¦ Patent No 3,729,549 to Gump et al i.ssued April 24, 1973 indicates that the ¦ fibers are sometimes oriented by hot drawing over a heated 6 ¦ shoe at a draw ratio of about 3:1 to about 7:1. In one 7 ¦ instance stretching PAN fibers some fourteen times reportedly 8 ¦ produced a fiber with a Young's modulus and strength of 2.7 x 9 ¦ 106 psi and 130 x 103 psi, respectivelyO
10 ¦ The denier of the resulting PAN fibers, such as those 11 usea as precursors for oxidation and carbonization, generally 12 measures from 1.3 to 3. The spinning and production of PAN
13 fibers with a denier of less than 1.3 as such precursors has 14 proven impractical, since such fibers have been heretofore too fragilP for process;ng.
16 To effect conversion of the PAN fibers, the latter are 17 heated to about 220C while exposed to oxygen or oxygen-lB containing gases such as air, nitrous oxide and sulphur 19 dioxide. The heating encourages the formation of a ladder structure~ while some of the CH2 groups are oxidized and HCN
21 is evolved. This may be ideall~ summarized as~
22 ~ O
24 \ ~ CH~ ~ CH2\ ~ \ ~ C ~ ~CH2~ ~ C ~ ~CH2 CH CH ~H + 2 ~ - CH CH CH CH
27 CN CN CN to ~C ~ ~C ~ ~C ~ CN
_ : ~
11S610~) 1 ¦ Some references in the prior a~k indicate that P~N fibers 2 ¦ should be prevented from shrirlkiny or drawn slightly during 3 ¦ oxidation in order ko restrain the P~N fibers from reverting 4 ¦ to their weak unstretched state. ~lowever, U.S~ Patent ~o.
~ 4,100,004, issued ~o Moss et al., indicates that some fibers 6 ¦ (not identified as to source) may generally be stretched by at 7 ~ least 50%, though no experimental values greater than 50% are 8 ¦ revealed and stretching of the fibers is generally limited to 9 ¦ resulting carbonized fiber diameters of 6 microns or more.
¦ Ihe ma~m amount o~ stretching indicated by ~le prior art is a~proximately 11 ¦ 95%, i.e. slightl~ less than double. H~ever, even a slight amount of stretch 12 ¦ ing during oxidation is generally avoided. In fact, general 13 ¦ industrial practice is to allow the fibers to shrink slightly 14 ¦ during oxidation in order to avoid any damage to the fibers at 15 ¦ this stage of the process.
16 ¦ The PAN fibers may be further oxidized at higher tem-17 1 peratures up to about 300C~ Thereafter, to effect 18 ¦ carbonization, the oxidized PAN fibers are heated to tem-19 ¦ peratures of 300 to 1400C in a nonoxidizing atmosphere, such 20 ¦ as-nitrogen, argon, helium or hydrogen. During this stage HCN
21 and other products from the decomposition reaction of PAN are 22 also released as gases. This release is accompanied by the 23 build-up in the fiber of ribbons consisting largely o~ carbon 24 atoms arranged in aromatic ring structures.
The strength and modulus of these carboni~ed fibers 26 increases rapidly up to about 1400C. However, while further 27 heating beyond about 1400C continues to increase the elastic 28 modulus, it reduces tensile strength, apparently because the ,~ _~w . ,/~
1 ~ ss~a~
s-tructure of the carhoni.~ed fibers hecomes rflo:re r~p~es~rl~at:i~fA
of true graphite. Conse~luent:Ly, cornrnerc-;al fiber-; are usually offered in a carbonlzed form with low mo~ulus and high strength or in graphitized forrn w:i-th high rnodulus and 10W
s-trength. For e~.ample, :in one case, heating P~N fibers from about 1400C to about 2400C reported:Ly resul-ted in a decrease in strength from approximately 3.1 GN/m2 (4.~8 x 10 psi) to 2~2 GN/m2 (3.2 x 105 psi), but an increase in the modulus from approximately 230 GN/m (33~4 x 106 psi~ to 500 GN/m (72.5 x 106 psi).
From the foreyoing it can be seen that restrictions on the size of precursor fiber employed and the amount to which the fibers can be stre-tched during oxidation, place l.imits on the strength and elasticity as well as the diameter of the resulting oxidized, carbonized or graphitized fibers produced.
~dditionally, in view of the relatively high temperatures involved, high inputs of energy are required to obtain an oxidized PA~, carbon or graphitized fiber of a given modulus and elasticity.
In one aspect the invention provides in a method of oxidizing fibers of an acrylic polymer comprising recurring acrvlonitrile units, wherein the fibers are oxidized in an oxidizing atmosphere heated to a temperature range between about 180C to about 300C preparatory to carbonization of the fibers, and dur.i.ng oxidation the fibers are drawn under tension, : the improvement comprising the steps of permeating the polymer with a carboxylic acid capable of forming its anhydride when heated to within the temperature range, and drawin~ the permeated fibers under tension during oxidation of the fibers in the atmosphere within the temperature range, the carhoxylic acid being present initial].y in -the polymer in an amount sufficient to permit improved drawing of the fiber to at least double
Particularly, the smaller the diameter of the fiber, the 16 greater is the ratio of surface area of the fiber to either 17 weight or volume. The greater ratio thus provides increased 18 fiber-to-matrix interface area, distributing the loading on 19 the composite over a greater area so as to improve interlami-nar shear strength markedly for composite materials utilizing 21 such smaller diameter fibers. Additionally, smaller diameter 22 fibers of improved strength and elasticity are considerably 23 more flexible than larger diameter fibers of similar strength 24 and elasticity, permitting formation of desirably thin woven fabrics or even braided and knitted fabrics, as composite pre-26 cursors.
27 Present methods for the production of PAN-based carbon 2a ~ fiber~ cal or the spinning of the PAN, followed by oxidation .
~ 11564~.'3 1 ¦ and carbonization of the resulting P~N fibeLs. ~rhe acrylo-2 ¦ nitrile monomer can be made by several known methods including 3 ¦ direct catalytic adc3ition of hydroyen cyanide to acetylene or 4 ¦ the addition of HCN to eth~lene oxide to give ethylene cyano-¦ hydrin, followed by dehydration. Polymerization is usually 6 ¦ carried out in an aqueous solution with the polymer precipi-7 ¦ tating from the system as a fine white powderO
8 ¦ Pure polyacrylonitrile is difficult to spin because it is 9 ¦ not sufficlently soluble in many organic solvents and is not 10 ¦ readily dyed. Consequently, polymers other than a pure PAN
11 ¦ homopolymer are often produced. Thus, a "PAN" fiber may 12 ¦ actually be an acrylic polymer formed primarily of recurring 13 ¦ acrylonitrile units copolymer~zed with a minor proportion of 14 ¦ methyl methacrylate, vinyl pyridine, vinyl chloride and the 15 ¦ like. Th'ese copolymers exhlbit properties substantially simi-16 ¦ lar to an acrylonitrile homopolymer~ By convention if the 17 ¦ fiber does not contain more than about 15 percent foreign 18 ¦ material it is refered to as polyacrylonitr'ile, and if more 19 ¦ than 15% then as modlfied acrylonitrile. Examples of such 20 ¦ copolymers include PAN fibers produced under trade names such 21 ¦ as Orlon* (E.I. DuPont de Nemours~, Courtelle SAF* (Courtaulds 22 ¦ Ltd.) and Acrilan (Chemstrand)~
23 ¦ The conversion o the PAN to fibers may be accomplished by 24 either dry or wet spinning. In the latter a salt solution of the polymer is extruded through a spinneret into a liquid which 26 can coagulate the PAN. In the dry spinning process a filament 27 is formed by the evaporation of a volatile solvent from a PAN
28 solution. In either case the filaments are subsequently *~trade mark 1 11564(~3 1 ¦ stretched to several times their original lenyth a~ a sliyhtl~
2 ¦ elevated temperature, for example 100C, so as to dra-" out and 3 ¦ align the m~in polymer chains and increase ln-~rchair-~dhesion. '~ur" U.S.
4 ¦ Patent No 3,729,549 to Gump et al i.ssued April 24, 1973 indicates that the ¦ fibers are sometimes oriented by hot drawing over a heated 6 ¦ shoe at a draw ratio of about 3:1 to about 7:1. In one 7 ¦ instance stretching PAN fibers some fourteen times reportedly 8 ¦ produced a fiber with a Young's modulus and strength of 2.7 x 9 ¦ 106 psi and 130 x 103 psi, respectivelyO
10 ¦ The denier of the resulting PAN fibers, such as those 11 usea as precursors for oxidation and carbonization, generally 12 measures from 1.3 to 3. The spinning and production of PAN
13 fibers with a denier of less than 1.3 as such precursors has 14 proven impractical, since such fibers have been heretofore too fragilP for process;ng.
16 To effect conversion of the PAN fibers, the latter are 17 heated to about 220C while exposed to oxygen or oxygen-lB containing gases such as air, nitrous oxide and sulphur 19 dioxide. The heating encourages the formation of a ladder structure~ while some of the CH2 groups are oxidized and HCN
21 is evolved. This may be ideall~ summarized as~
22 ~ O
24 \ ~ CH~ ~ CH2\ ~ \ ~ C ~ ~CH2~ ~ C ~ ~CH2 CH CH ~H + 2 ~ - CH CH CH CH
27 CN CN CN to ~C ~ ~C ~ ~C ~ CN
_ : ~
11S610~) 1 ¦ Some references in the prior a~k indicate that P~N fibers 2 ¦ should be prevented from shrirlkiny or drawn slightly during 3 ¦ oxidation in order ko restrain the P~N fibers from reverting 4 ¦ to their weak unstretched state. ~lowever, U.S~ Patent ~o.
~ 4,100,004, issued ~o Moss et al., indicates that some fibers 6 ¦ (not identified as to source) may generally be stretched by at 7 ~ least 50%, though no experimental values greater than 50% are 8 ¦ revealed and stretching of the fibers is generally limited to 9 ¦ resulting carbonized fiber diameters of 6 microns or more.
¦ Ihe ma~m amount o~ stretching indicated by ~le prior art is a~proximately 11 ¦ 95%, i.e. slightl~ less than double. H~ever, even a slight amount of stretch 12 ¦ ing during oxidation is generally avoided. In fact, general 13 ¦ industrial practice is to allow the fibers to shrink slightly 14 ¦ during oxidation in order to avoid any damage to the fibers at 15 ¦ this stage of the process.
16 ¦ The PAN fibers may be further oxidized at higher tem-17 1 peratures up to about 300C~ Thereafter, to effect 18 ¦ carbonization, the oxidized PAN fibers are heated to tem-19 ¦ peratures of 300 to 1400C in a nonoxidizing atmosphere, such 20 ¦ as-nitrogen, argon, helium or hydrogen. During this stage HCN
21 and other products from the decomposition reaction of PAN are 22 also released as gases. This release is accompanied by the 23 build-up in the fiber of ribbons consisting largely o~ carbon 24 atoms arranged in aromatic ring structures.
The strength and modulus of these carboni~ed fibers 26 increases rapidly up to about 1400C. However, while further 27 heating beyond about 1400C continues to increase the elastic 28 modulus, it reduces tensile strength, apparently because the ,~ _~w . ,/~
1 ~ ss~a~
s-tructure of the carhoni.~ed fibers hecomes rflo:re r~p~es~rl~at:i~fA
of true graphite. Conse~luent:Ly, cornrnerc-;al fiber-; are usually offered in a carbonlzed form with low mo~ulus and high strength or in graphitized forrn w:i-th high rnodulus and 10W
s-trength. For e~.ample, :in one case, heating P~N fibers from about 1400C to about 2400C reported:Ly resul-ted in a decrease in strength from approximately 3.1 GN/m2 (4.~8 x 10 psi) to 2~2 GN/m2 (3.2 x 105 psi), but an increase in the modulus from approximately 230 GN/m (33~4 x 106 psi~ to 500 GN/m (72.5 x 106 psi).
From the foreyoing it can be seen that restrictions on the size of precursor fiber employed and the amount to which the fibers can be stre-tched during oxidation, place l.imits on the strength and elasticity as well as the diameter of the resulting oxidized, carbonized or graphitized fibers produced.
~dditionally, in view of the relatively high temperatures involved, high inputs of energy are required to obtain an oxidized PA~, carbon or graphitized fiber of a given modulus and elasticity.
In one aspect the invention provides in a method of oxidizing fibers of an acrylic polymer comprising recurring acrvlonitrile units, wherein the fibers are oxidized in an oxidizing atmosphere heated to a temperature range between about 180C to about 300C preparatory to carbonization of the fibers, and dur.i.ng oxidation the fibers are drawn under tension, : the improvement comprising the steps of permeating the polymer with a carboxylic acid capable of forming its anhydride when heated to within the temperature range, and drawin~ the permeated fibers under tension during oxidation of the fibers in the atmosphere within the temperature range, the carhoxylic acid being present initial].y in -the polymer in an amount sufficient to permit improved drawing of the fiber to at least double
-5-cb/!
'~', ~ 1 56~9 the oriy:inal f:it)er ]encJt:h, and to an avera(3e fiber diatrleter of less than 10 m:icrons.
The inventiorl also provides novel fiher.c,.
The invention i~ basically accomplishecl by mixing the acrylic polymer with a carboxyl:ic acid 50 tha-t the po:Ly-mer fiber is perrneated therewith, the acid being one which, upon heating the fiber to an oxidiziny ternperature, ,1" ,j'` cb/l i,,~) ~6~
1 will form the anhyc]ride correspondin~ ~o that acid (and it is 2 postulated that the anhydride will equilihrate within the 3 fiber with the acid); oxidizing the treated fibers in an 4 oxidizing atmosphere; and stretching the fibers during the oxidation process. The acid and/or its anhydride appears to
'~', ~ 1 56~9 the oriy:inal f:it)er ]encJt:h, and to an avera(3e fiber diatrleter of less than 10 m:icrons.
The inventiorl also provides novel fiher.c,.
The invention i~ basically accomplishecl by mixing the acrylic polymer with a carboxyl:ic acid 50 tha-t the po:Ly-mer fiber is perrneated therewith, the acid being one which, upon heating the fiber to an oxidiziny ternperature, ,1" ,j'` cb/l i,,~) ~6~
1 will form the anhyc]ride correspondin~ ~o that acid (and it is 2 postulated that the anhydride will equilihrate within the 3 fiber with the acid); oxidizing the treated fibers in an 4 oxidizing atmosphere; and stretching the fibers during the oxidation process. The acid and/or its anhydride appears to
6 act as a plasticizer and reduces the fiber yield stress and
7 increases fiber plasticity such that during oxidation the
8 treated fibers may be drawn by at least 40~ and as much as
9 300~ or more than similar but untreated fibers. The acid should be present in the fiber during oxidation, in a quantity 11 sufficient to improve the stretchability the noted amount.
12 The relative amount of acid used depends then upon such fac-13 tors as the nature of the acid, the choice of the particular 14 fiber as to constituents and diameter, the length of time allowed to permit the acid to permeate the fiber to some 16 desired extent, etc~ and can easily be determined empirically 17 for each set of parameters.
18 ~ther objects of the invention will in part be obvious and 19 will in part appear hereinafter. The invention accordingly comprises the processes involving the several steps and the 21 relation and order of one or more of such steps with respect 22 to each of the others, and the products possessing the 23 features, properties and relation of elements which are 24 exemplified in the following detailed disclosure and the scope of the application all of which will be indicated in the claims.
26 For a fuller understanding of the nature and objects of 27 the present invention, reference should be had to the 28 ~ following ailed desc~ ~tion taken in connection with the ~ 1~S6~
1 ¦ accompanying drawing wherein:
2 ¦ Fig. 1 is a sch~!atic of the apparatus used to carry out ¦ one embodiment of the present invention; and 4 ¦ Fig. 2 is a representation of a typical temperature gra-¦ dient of an oxidation furnace employed in one embodiment of 6 ¦ the instant invention.
7 Referring now to Fig. 1, PAN fibers in the form of a 8 multifilament sheet, tow or web, 20, are pulled from fiber 9 supply spool, 22, by constant speed devicel 24, which comprises a pair of electric drive rollers, 25 and 260 11 Tensioning device 28 of known type, typically comprising three 12 rollers, 29, 30, and 31, in conjunction with take-up device 32 13 is intended to place the mul~ifilament sheet, tow or web in 14 sufficient uniform tension to draw the PAN fibers to the extent desired during oxidation~ In this regard it is pre-16 ferable to stretch the PAN fibers during the Qxidation process, 17 more than the prior art and up to as much as quadruple the 18 stretchabili~y of the untreated fibers, since the greater the ]9 stretching accomplished, the more one will achieve the pur-poses of the invention to produce higher strength and modulus 21 fibers.
Z2 The fiber tow 20, is then transferred under tension 23 through an oxidation chamber such as multizone gradient fur-24 nace 34, so as to provide a proper residence time, as discussed below. Upon leaving furnace 34 the oxidized and 26 stretched PAN fiber of tow 20 is taken up on known constant 27 speed take-up device 32, before being passed to a carbonizing 28 zone for further treatment.
1 ~1S6~9 1 ¦ During subsequent carbonization by well-known techinque~, 2 ¦ the oxidized P~N fibers are heated in a nonoxidizing ato-3 ¦ mosphere, such as nitrogen, argon, helium or hydrogen to tem~
4 ¦ peratures of about 300 to 1400C. The strength and modulus of ¦ the oxidized fibers increases rapidly during this stage as 6 ¦ carbon dioxide, water, carbon monoxide, HCN, NH3, and other 7 1 products are released and aromatic ring structures of carbon 8 ¦ are formed. The carbonized fibers may then be further heated 9 ¦ and graphitiæed under an inert gas at temperatures up to 3000
12 The relative amount of acid used depends then upon such fac-13 tors as the nature of the acid, the choice of the particular 14 fiber as to constituents and diameter, the length of time allowed to permit the acid to permeate the fiber to some 16 desired extent, etc~ and can easily be determined empirically 17 for each set of parameters.
18 ~ther objects of the invention will in part be obvious and 19 will in part appear hereinafter. The invention accordingly comprises the processes involving the several steps and the 21 relation and order of one or more of such steps with respect 22 to each of the others, and the products possessing the 23 features, properties and relation of elements which are 24 exemplified in the following detailed disclosure and the scope of the application all of which will be indicated in the claims.
26 For a fuller understanding of the nature and objects of 27 the present invention, reference should be had to the 28 ~ following ailed desc~ ~tion taken in connection with the ~ 1~S6~
1 ¦ accompanying drawing wherein:
2 ¦ Fig. 1 is a sch~!atic of the apparatus used to carry out ¦ one embodiment of the present invention; and 4 ¦ Fig. 2 is a representation of a typical temperature gra-¦ dient of an oxidation furnace employed in one embodiment of 6 ¦ the instant invention.
7 Referring now to Fig. 1, PAN fibers in the form of a 8 multifilament sheet, tow or web, 20, are pulled from fiber 9 supply spool, 22, by constant speed devicel 24, which comprises a pair of electric drive rollers, 25 and 260 11 Tensioning device 28 of known type, typically comprising three 12 rollers, 29, 30, and 31, in conjunction with take-up device 32 13 is intended to place the mul~ifilament sheet, tow or web in 14 sufficient uniform tension to draw the PAN fibers to the extent desired during oxidation~ In this regard it is pre-16 ferable to stretch the PAN fibers during the Qxidation process, 17 more than the prior art and up to as much as quadruple the 18 stretchabili~y of the untreated fibers, since the greater the ]9 stretching accomplished, the more one will achieve the pur-poses of the invention to produce higher strength and modulus 21 fibers.
Z2 The fiber tow 20, is then transferred under tension 23 through an oxidation chamber such as multizone gradient fur-24 nace 34, so as to provide a proper residence time, as discussed below. Upon leaving furnace 34 the oxidized and 26 stretched PAN fiber of tow 20 is taken up on known constant 27 speed take-up device 32, before being passed to a carbonizing 28 zone for further treatment.
1 ~1S6~9 1 ¦ During subsequent carbonization by well-known techinque~, 2 ¦ the oxidized P~N fibers are heated in a nonoxidizing ato-3 ¦ mosphere, such as nitrogen, argon, helium or hydrogen to tem~
4 ¦ peratures of about 300 to 1400C. The strength and modulus of ¦ the oxidized fibers increases rapidly during this stage as 6 ¦ carbon dioxide, water, carbon monoxide, HCN, NH3, and other 7 1 products are released and aromatic ring structures of carbon 8 ¦ are formed. The carbonized fibers may then be further heated 9 ¦ and graphitiæed under an inert gas at temperatures up to 3000
10 ¦ C. Both carbonization and graphitization may be carried out
11 in one or more stages, during which the fibers are generally
12 placed under some tension. Further details of such treatment
13 are not believed to be required herein, since such are well
14 known in the prior art as illustrated by Mos.s et al. in U.S.
Patent No. 4,100,004 and Gump et al in U.S. Patent No.
16 3,729,549.
17 Multizone gradient furnace 34 comprises a number of 18 heating zones preferably ranging in temperature from a low of 19 about 200C to a high of about 260C, but varying from as much as 180C at the entrance to 300C at the exit of the furnace.
21 A typical temperature gradient is depicted in Eigure 2 in 22 terms of temperature of the furnace atmosphere at a given 23 distance from the furnace entrance. Of course, a series of 24 separate furnaces with one or more heating zones may be employed to establish a series of temperature stages.
26 Likewise, a single heating zone furnace held at a particular 27 temperature may also be appropriate depending upon the ulti-28 ~ mate prope es desired in the fiber product.
_g_ 1 115~409 1 ¦ An oxygenation medium comprising oxygen and oxygen con-2 ¦ taining yases such as air, nitrous oxide and sulphur dioxide 3 ¦ is supplied to furnace 34 by line 36. Although only 4 ¦ shown as supplied at the inlet of furnace 34, the oxygenation ¦ medium may be injected into the furnace at various points 6 ¦ along the path of the fibers as they are oxidized.
7 ¦ Pressure relief and recirculation of the oxidation reac-8 ¦ tion and thermal decomposition products of PAN as well as any 9 ¦ unreacted gases can be achieved by venting furnace 34 through 10 ¦ line 38, although it may be desirable to permit the gases in 11 ¦ the furnace to remain relatively stagnant to encourage the 12 ¦ postulated equilibrium between the vaporized acld and its 13 anyhydride in the fiber. A main component of these decom-14 position products is HCN, particularly during oxidation of the fibers. However, other components include CO, CO2, H20, NH3, 16 as well as a number of intermediate hydrocarbons and nitriles, 17 including acetonitrile and acrylonitrile.
18 In accordance with the present invention, a carboxylic 19 acid which, at the temperatures used to oxidize the fiber, will substantially vaporize and convert to the corresponding 21 anhydride with which the acid can be in material equilibrium 22 at least in the fiber in part, is mixed with the PAN fiber.
23 Inasmuch as such temperatures are in the range of about 180 to 24 300C, it is apparent that formic acid is excluded insamuch as it decomposes at such temperatures and does not form an an-26 hydride. Other carboxylic acids may not vaporize at such tem-27 peratures or may not thermally form their anhydride in suffi-28 cient amounts to maintain a substantially balanced equilibrium ~ 115~0~
1 ¦ i.e. the reaction goes virtually to completion in one direc-2 ¦ tion or the other. Thus, both mono and polycarboxylic acids 3 ¦ are useful. Typically, such diverse carboxylic acids as ace-I tic acid and itaconic acid are acceptable for purposes of the invention~ Mixing of the fiber and acid can occur in the ori-6 ginal manufacturing process for the fiber, or the fiber can 7 be permeated or impregnated with the carboxylic acid by imbi-8 bition in an appropriate solution of the acid. The imbibition 9 time to impregnate the fiber depends upon the composition of the fiber, particularly the na~ure of the interstitial voids 11 provided by the introduction of copolymers and other materials 12 into the original fiber. Typically, imbibition times of from 13 one minute to several hours can be used, but the longer imbi-14 bition times seem to provide the better results.
The plasticizing action of the carboxylic acid and/or its 16 anhydride is believed to facilitate molec~lar motion in the 17 PAN fibers. In any event, some acids may be less readily 18 absorbed in the PAN fiber than others, depending upon the 19 steric aspects of the acid and the molecular structure of the particular fiber. Thus, care must be taken to insure proper 21 mixture of fiber polymer and concentration of the acid, both 22 in amount and in time as the case may be, to allow absorption 23 of the latter into the acrylic fibers. ~lomopolymer acrylo-24 nitrile exhibits little if any permeation by carboxylic acids25 from a soaking bath, even over extended periods of time, so 26 the desired acid should be incorporated into the fiber pre-27 ferably at the time of spinning.
~8 In acc ance with the present invention, fiber residence .. . .. ..
1 1~56~1~'3 1 ¦time in the furnace should generally not be less than 2 minu-2 ¦tes, and is preferab~y in the range from 2 minutes to 120 3 ¦minutes, since the plasticizing effect is not lmmediate.
4 ¦ Consequently, oxidizing the fibers slowly is favored~
¦ In this regard the acrylic polymer which is utilized in 6 ¦ the present process is formed either entirely of recurring 7 ¦ acrylonitrile units, or of recurring acrylonitrile units copo-~ ¦ lymerized with a minor proportion of one or more vinyl 9 ¦ units to produce a copolymer exhibiting properties substan-10 ¦ tially similar to an acrylonitrile homopolymer, particularly 11 ¦ with regard to the time needed to undergo oxidation. As to 12 the temperature used in the oxidation process, while acrylo-13 nitrile homopolymers can be used in the present process, other 14 PAN copolymer fibers which oxidize over a wide temperature range are preferred.
16 In the prior art, the acrylic fibers were stretched, if at 17 all, during oxidation by approximately not more than 95%
18 their original length. In contrast the treatment of the 19 fibers with carboxylic acid in accordance with the present inventiont allows the treated acrylic fibers to be stretched 21 during oxidation, as much as 300~ or more compared to the 22 untreated fiber, thus increasing the ultimate strength and 23 modulus of the resulting carbon fibers by as much as 40% and 24 50% or more, respectively. The increase in the strength and e]asticity of the oxidized acrylic fibers is believed to occur 26 because improved extension of the fibers causes greater chain 27 orientation than has been heretofore possible.
28 A9 rea ly appreciated by those skilled i- the art, these 115~4~
1 improved properties are obtained at llttle or no increase in 2 cost, since the plasticizing effect may be obtained by simple 3 addition of inexpenslve carboxylic acids to the fiber. Addition-4 ally, overall energy requirements to produce a given strength or modulus of oxidized or carbonized PAN fiber are reduced, 6 since the fibers obtain greater strength and elasticity at an 7 earlier stage of the process, thus reducing the number of sta-8 ges and the extent of heating required. Concomitant equipment 9 savings are likewise obvious to those skilled in the art.
Use of the carboxylic acid and/or its anhydride at the 11 oxidizing temperatures as a plasticizing rnedium also allows 12 smaller size fiber precursors to be processed and smaller 13 diameter oxldized PAN and carbon fibers to be produced than 14 previously possible. Prior art processes required precursor fibers of at least approximately 1.3 denier, or greater, and 16 produced oxidized PAN fibers of 12 microns or larger in 17 diameter and carbon fibers of 6 microns or more in diameter.
18 In contrast, the present invention allows the processing of 19 fiber precursors of 1.2 denier or less and the production of oxidized PAN fibers as small as 3 microns in diameter as well 21 as carbon fibers of as small as 2 microns in diameter with 22 little or no increase in process requirements.
23 The following examples ~urther illustrate the invention 24 and the advantages resulting therefrom. These examples are presented solely for illustration, such that the invention 26 sho~ld not be construed as being limited to the particular 27 conditions set forth in the examples.
.~
. . . Il 1 11S6~09 1 ¦ EXAMPLE I
2 ~
3 ¦ E. I. DuPon~ Or~on* brand ~iber is a cornrnercially available 4 ¦PAN fiber with copolymer units interspersed throughout the ¦ fiber structure. On information and belief, the composition 6 ¦of the fiber is 94~ polyacrylonitrile and 6% methyl acrylate.
7 ¦ A thermal gradient from 220 to 240C was established in fur-8 ¦ nace 34 in several steps. Pure oxygen served as the oxygena-9 I tion medium supplied through line 36. The drawn and oxidized 10 ¦ PAN fiber, untreated with any acid, exhibited a maximum draw 11 ¦ ratio of 1.27, corresponding to a 27~ elongationO
13 ¦ EXAMPLE II
Example I was repeated, but prior to oxidizing the PAN
16 iber, the latter was soaked for one minute in a 8.3% itaconic 17 acid solution in a dip tank, then put throuyh squeeze rolls to 18 express excess fluid, and placed into the oxidiæing chamber.
19 On drawing the fiber during oxidation to a maximum temperature of 255C, a maximum draw ratio of 1.44 was obtained, an im-21 provement of .20 in the draw ratio.
24 _ Example II was repeated but the fiber was after soaking, 26 additionally pretreated in air saturated with 8.5% itaconic 27 acid solution at 190C for four hours beore oxidation. In 28 this instance, a maximum draw ratio of 1.56 was obtained.
ll b/ e mark 1 S 6'1 0 s~
I ~1 EXAMPLE IV
3 ¦ Courtauld's S~F Courtelle*~ib~r (hereinafter referrred to 4 ¦ as SPF ) is a commerciall~ availab~e PAN fiher with copolymer 5 ¦ units interspersed throughout the ~iber structure. This fiber ¦ is believed to differ from the DuPont Orlon* brand of acrylic 7 ¦ fiber used in Example I in that, on information and belief, the 8 ¦ composition of the Courtelle* fiber is 93% polyacrylonitrile, 9 ¦ 6% methyl acry]ate and 1~ itaconic acid. An SAF* 3000 fiber 10¦ tow o~ 1.2 d'tex of this Courtelle* fiber was drawn in three 11¦ stages to 300% during oxidation with a residence time of about 12¦ 1 hour. A thermal graaient from 220C to 260C was establish-13¦ ed in furnace 34 in three steps of 10 to 20 degrees each ~i.e.
14~ 220-230, 230-240, 240-260). Pure oxygen served as the oxyge-
Patent No. 4,100,004 and Gump et al in U.S. Patent No.
16 3,729,549.
17 Multizone gradient furnace 34 comprises a number of 18 heating zones preferably ranging in temperature from a low of 19 about 200C to a high of about 260C, but varying from as much as 180C at the entrance to 300C at the exit of the furnace.
21 A typical temperature gradient is depicted in Eigure 2 in 22 terms of temperature of the furnace atmosphere at a given 23 distance from the furnace entrance. Of course, a series of 24 separate furnaces with one or more heating zones may be employed to establish a series of temperature stages.
26 Likewise, a single heating zone furnace held at a particular 27 temperature may also be appropriate depending upon the ulti-28 ~ mate prope es desired in the fiber product.
_g_ 1 115~409 1 ¦ An oxygenation medium comprising oxygen and oxygen con-2 ¦ taining yases such as air, nitrous oxide and sulphur dioxide 3 ¦ is supplied to furnace 34 by line 36. Although only 4 ¦ shown as supplied at the inlet of furnace 34, the oxygenation ¦ medium may be injected into the furnace at various points 6 ¦ along the path of the fibers as they are oxidized.
7 ¦ Pressure relief and recirculation of the oxidation reac-8 ¦ tion and thermal decomposition products of PAN as well as any 9 ¦ unreacted gases can be achieved by venting furnace 34 through 10 ¦ line 38, although it may be desirable to permit the gases in 11 ¦ the furnace to remain relatively stagnant to encourage the 12 ¦ postulated equilibrium between the vaporized acld and its 13 anyhydride in the fiber. A main component of these decom-14 position products is HCN, particularly during oxidation of the fibers. However, other components include CO, CO2, H20, NH3, 16 as well as a number of intermediate hydrocarbons and nitriles, 17 including acetonitrile and acrylonitrile.
18 In accordance with the present invention, a carboxylic 19 acid which, at the temperatures used to oxidize the fiber, will substantially vaporize and convert to the corresponding 21 anhydride with which the acid can be in material equilibrium 22 at least in the fiber in part, is mixed with the PAN fiber.
23 Inasmuch as such temperatures are in the range of about 180 to 24 300C, it is apparent that formic acid is excluded insamuch as it decomposes at such temperatures and does not form an an-26 hydride. Other carboxylic acids may not vaporize at such tem-27 peratures or may not thermally form their anhydride in suffi-28 cient amounts to maintain a substantially balanced equilibrium ~ 115~0~
1 ¦ i.e. the reaction goes virtually to completion in one direc-2 ¦ tion or the other. Thus, both mono and polycarboxylic acids 3 ¦ are useful. Typically, such diverse carboxylic acids as ace-I tic acid and itaconic acid are acceptable for purposes of the invention~ Mixing of the fiber and acid can occur in the ori-6 ginal manufacturing process for the fiber, or the fiber can 7 be permeated or impregnated with the carboxylic acid by imbi-8 bition in an appropriate solution of the acid. The imbibition 9 time to impregnate the fiber depends upon the composition of the fiber, particularly the na~ure of the interstitial voids 11 provided by the introduction of copolymers and other materials 12 into the original fiber. Typically, imbibition times of from 13 one minute to several hours can be used, but the longer imbi-14 bition times seem to provide the better results.
The plasticizing action of the carboxylic acid and/or its 16 anhydride is believed to facilitate molec~lar motion in the 17 PAN fibers. In any event, some acids may be less readily 18 absorbed in the PAN fiber than others, depending upon the 19 steric aspects of the acid and the molecular structure of the particular fiber. Thus, care must be taken to insure proper 21 mixture of fiber polymer and concentration of the acid, both 22 in amount and in time as the case may be, to allow absorption 23 of the latter into the acrylic fibers. ~lomopolymer acrylo-24 nitrile exhibits little if any permeation by carboxylic acids25 from a soaking bath, even over extended periods of time, so 26 the desired acid should be incorporated into the fiber pre-27 ferably at the time of spinning.
~8 In acc ance with the present invention, fiber residence .. . .. ..
1 1~56~1~'3 1 ¦time in the furnace should generally not be less than 2 minu-2 ¦tes, and is preferab~y in the range from 2 minutes to 120 3 ¦minutes, since the plasticizing effect is not lmmediate.
4 ¦ Consequently, oxidizing the fibers slowly is favored~
¦ In this regard the acrylic polymer which is utilized in 6 ¦ the present process is formed either entirely of recurring 7 ¦ acrylonitrile units, or of recurring acrylonitrile units copo-~ ¦ lymerized with a minor proportion of one or more vinyl 9 ¦ units to produce a copolymer exhibiting properties substan-10 ¦ tially similar to an acrylonitrile homopolymer, particularly 11 ¦ with regard to the time needed to undergo oxidation. As to 12 the temperature used in the oxidation process, while acrylo-13 nitrile homopolymers can be used in the present process, other 14 PAN copolymer fibers which oxidize over a wide temperature range are preferred.
16 In the prior art, the acrylic fibers were stretched, if at 17 all, during oxidation by approximately not more than 95%
18 their original length. In contrast the treatment of the 19 fibers with carboxylic acid in accordance with the present inventiont allows the treated acrylic fibers to be stretched 21 during oxidation, as much as 300~ or more compared to the 22 untreated fiber, thus increasing the ultimate strength and 23 modulus of the resulting carbon fibers by as much as 40% and 24 50% or more, respectively. The increase in the strength and e]asticity of the oxidized acrylic fibers is believed to occur 26 because improved extension of the fibers causes greater chain 27 orientation than has been heretofore possible.
28 A9 rea ly appreciated by those skilled i- the art, these 115~4~
1 improved properties are obtained at llttle or no increase in 2 cost, since the plasticizing effect may be obtained by simple 3 addition of inexpenslve carboxylic acids to the fiber. Addition-4 ally, overall energy requirements to produce a given strength or modulus of oxidized or carbonized PAN fiber are reduced, 6 since the fibers obtain greater strength and elasticity at an 7 earlier stage of the process, thus reducing the number of sta-8 ges and the extent of heating required. Concomitant equipment 9 savings are likewise obvious to those skilled in the art.
Use of the carboxylic acid and/or its anhydride at the 11 oxidizing temperatures as a plasticizing rnedium also allows 12 smaller size fiber precursors to be processed and smaller 13 diameter oxldized PAN and carbon fibers to be produced than 14 previously possible. Prior art processes required precursor fibers of at least approximately 1.3 denier, or greater, and 16 produced oxidized PAN fibers of 12 microns or larger in 17 diameter and carbon fibers of 6 microns or more in diameter.
18 In contrast, the present invention allows the processing of 19 fiber precursors of 1.2 denier or less and the production of oxidized PAN fibers as small as 3 microns in diameter as well 21 as carbon fibers of as small as 2 microns in diameter with 22 little or no increase in process requirements.
23 The following examples ~urther illustrate the invention 24 and the advantages resulting therefrom. These examples are presented solely for illustration, such that the invention 26 sho~ld not be construed as being limited to the particular 27 conditions set forth in the examples.
.~
. . . Il 1 11S6~09 1 ¦ EXAMPLE I
2 ~
3 ¦ E. I. DuPon~ Or~on* brand ~iber is a cornrnercially available 4 ¦PAN fiber with copolymer units interspersed throughout the ¦ fiber structure. On information and belief, the composition 6 ¦of the fiber is 94~ polyacrylonitrile and 6% methyl acrylate.
7 ¦ A thermal gradient from 220 to 240C was established in fur-8 ¦ nace 34 in several steps. Pure oxygen served as the oxygena-9 I tion medium supplied through line 36. The drawn and oxidized 10 ¦ PAN fiber, untreated with any acid, exhibited a maximum draw 11 ¦ ratio of 1.27, corresponding to a 27~ elongationO
13 ¦ EXAMPLE II
Example I was repeated, but prior to oxidizing the PAN
16 iber, the latter was soaked for one minute in a 8.3% itaconic 17 acid solution in a dip tank, then put throuyh squeeze rolls to 18 express excess fluid, and placed into the oxidiæing chamber.
19 On drawing the fiber during oxidation to a maximum temperature of 255C, a maximum draw ratio of 1.44 was obtained, an im-21 provement of .20 in the draw ratio.
24 _ Example II was repeated but the fiber was after soaking, 26 additionally pretreated in air saturated with 8.5% itaconic 27 acid solution at 190C for four hours beore oxidation. In 28 this instance, a maximum draw ratio of 1.56 was obtained.
ll b/ e mark 1 S 6'1 0 s~
I ~1 EXAMPLE IV
3 ¦ Courtauld's S~F Courtelle*~ib~r (hereinafter referrred to 4 ¦ as SPF ) is a commerciall~ availab~e PAN fiher with copolymer 5 ¦ units interspersed throughout the ~iber structure. This fiber ¦ is believed to differ from the DuPont Orlon* brand of acrylic 7 ¦ fiber used in Example I in that, on information and belief, the 8 ¦ composition of the Courtelle* fiber is 93% polyacrylonitrile, 9 ¦ 6% methyl acry]ate and 1~ itaconic acid. An SAF* 3000 fiber 10¦ tow o~ 1.2 d'tex of this Courtelle* fiber was drawn in three 11¦ stages to 300% during oxidation with a residence time of about 12¦ 1 hour. A thermal graaient from 220C to 260C was establish-13¦ ed in furnace 34 in three steps of 10 to 20 degrees each ~i.e.
14~ 220-230, 230-240, 240-260). Pure oxygen served as the oxyge-
15¦ nativn medium supplied through line 36. The maximum draw ratio
16¦ was 3.08 resulting in a 208% elongation at the end of the
17¦ first oxidation stage (max. temp. 243C)~ a considerable
18¦ improvement over the similar DuPont fiber in which no car-
19 boxylic acid was present prior to treatment~
Four tows of the stretched fiber were collimated to make 21 one 12,000 fiber tow during the last step of the oxidation 22 process. The drawn and oxidized PAN fiber was then carbonized 23 continuously between 300 and 900C under nitrogen and there-24 after graphitized under nitrogen at 1400C and at 2300C in two steps. The graphite fiber diameter was found to be 26 approximately 3 microns and a tensile strength of 46 x 104 psi 27 and tensilé modulus of 64 x 106 psi were observed. This 28 represents a 31~ increase in tensile strength and a 30%
, -15-* trade mark 1 increase in the modulus, since a yraphitized fiber prepared 2 under identical conditions, but without drawing and use o a 3 plasticizing medium during oxidation, had a diameter o 4 approximately 7 microns with a tensile strength of 35 x 104 psi and a tensile modulus of 50 x lU5 psi.
9 Example IV was repeated, but prior to oxidizing the PAN
fiber, the latter was soaked for one minute in a 6% itaconic 11 acid solution in a dip tank, then put through squee~e rolls to 12 express excess fluid, and placed into the oxidizing chamber.
13 On drawing the iber during oxidation, a draw ratio o 3.61 14 was obtained.
1 Example V was repeated three times but in each case the 1 PAN fiber was soaked in a only water. Upon drawing the fiber 2 during oxidat;onl respective draw ratios of 3.03, 3.03 and 2 3.17 were observed, in excellent agreement with the results of 2 Example IV.
2 Example V was repeated using 10% acetic acid solution as 2 the dip. On fiber drawing the observed maximum draw ratio was 2 3.60.
!
liS~;409 1 ¦ EXAMPLE VIII
2 l 3 ¦ Example V was repeated using a 1~ acetic acid solution as 4 ¦ the dip. A draw ratio of 3.37 was obtained upon drawing the 5 ¦ fiber.
7 Although the invention has been described with preferred 8 embodiments, it is to be understood that variations and modi-9 fications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to 11 be considered within the purview and scope of the following 12 claims.
. . . il . .
Four tows of the stretched fiber were collimated to make 21 one 12,000 fiber tow during the last step of the oxidation 22 process. The drawn and oxidized PAN fiber was then carbonized 23 continuously between 300 and 900C under nitrogen and there-24 after graphitized under nitrogen at 1400C and at 2300C in two steps. The graphite fiber diameter was found to be 26 approximately 3 microns and a tensile strength of 46 x 104 psi 27 and tensilé modulus of 64 x 106 psi were observed. This 28 represents a 31~ increase in tensile strength and a 30%
, -15-* trade mark 1 increase in the modulus, since a yraphitized fiber prepared 2 under identical conditions, but without drawing and use o a 3 plasticizing medium during oxidation, had a diameter o 4 approximately 7 microns with a tensile strength of 35 x 104 psi and a tensile modulus of 50 x lU5 psi.
9 Example IV was repeated, but prior to oxidizing the PAN
fiber, the latter was soaked for one minute in a 6% itaconic 11 acid solution in a dip tank, then put through squee~e rolls to 12 express excess fluid, and placed into the oxidizing chamber.
13 On drawing the iber during oxidation, a draw ratio o 3.61 14 was obtained.
1 Example V was repeated three times but in each case the 1 PAN fiber was soaked in a only water. Upon drawing the fiber 2 during oxidat;onl respective draw ratios of 3.03, 3.03 and 2 3.17 were observed, in excellent agreement with the results of 2 Example IV.
2 Example V was repeated using 10% acetic acid solution as 2 the dip. On fiber drawing the observed maximum draw ratio was 2 3.60.
!
liS~;409 1 ¦ EXAMPLE VIII
2 l 3 ¦ Example V was repeated using a 1~ acetic acid solution as 4 ¦ the dip. A draw ratio of 3.37 was obtained upon drawing the 5 ¦ fiber.
7 Although the invention has been described with preferred 8 embodiments, it is to be understood that variations and modi-9 fications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to 11 be considered within the purview and scope of the following 12 claims.
. . . il . .
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of oxidizing fibers of an acrylic polymer comprising recurring acrylonitrile units, wherein said fibers are oxidized in an oxidizing atmosphere heated to a temperature range between about 180°C to about 300°C
preparatory to carbonization of said fibers, and during oxidation said fibers are drawn under tension, the improve-ment comprising the steps of permeating said polymer with a carboxylic acid capable of forming its anhydride when heated to within said temperature range, and drawing said permeated fibers under tension during oxidation of said fibers in said atmosphere within said temperature range, said carboxylic acid being present initially in said polymer in an amount sufficient to permit improved drawing of the fiber to at least double the original fiber length, and to an average fiber diameter of less than 10 microns.
preparatory to carbonization of said fibers, and during oxidation said fibers are drawn under tension, the improve-ment comprising the steps of permeating said polymer with a carboxylic acid capable of forming its anhydride when heated to within said temperature range, and drawing said permeated fibers under tension during oxidation of said fibers in said atmosphere within said temperature range, said carboxylic acid being present initially in said polymer in an amount sufficient to permit improved drawing of the fiber to at least double the original fiber length, and to an average fiber diameter of less than 10 microns.
2. A process according to claim 1 wherein said polymer is acrylonitrile homopolymer.
3. A process according to claim 1 wherein said polymer is an acrylonitrile polymer containing at least about 85 mole percent of acrylonitrile units copolymerized with at least another material.
4. A process according to claim 1 wherein said acid is a monocarboxylic acid.
5. A process according to claim 1 wherein said acid is a dicarboxylic acid.
6. A process according to claim 1 wherein said acid is selected from the group consisting of acetic and itaconic acids.
7. A process according to claim 1 wherein said fiber is maintained in said atmosphere for a period of between about 2 to 120 minutes.
8. A process according to claim 1 including the step of establishing a temperature gradient along said fibers from about 220°C to about 260°C during said oxidation.
9. A process according to claim 1 wherein said drawing of the fibers is in excess of double the original length of said fibers.
10. A process according to claim 1 including the step of treating the fiber with said acid in a soaking bath before disposing said fibers within said oxygen-containing atmosphere.
11. A process according to claim 1 wherein said acid is incorporated in said fibers during or prior to the original formation of the latter.
12. An oxidized fiber produced from a polyacrylonitrile precursor permeated with a carboxylic acid prior to oxidation, said fiber having been drawn under tension during oxidation to an elongation of more than double the original length of the fiber and to an average diameter of less than 10 microns.
13. A graphitized fiber produced from polyacrylonitrile precursor fiber and having a tensile strength of approximately 52 x 104 psi, a modulus of approximatelv 76 x 106 psi and a diameter of about 4.5 microns or less.
14. A graphitized fiber produced from polyacrylonitrile precursor fiber and having a tensile strength of approximately 42 x 104, a modulus of approximately 64 x 106 psi and a diameter of about 4.5 microns or less.
15. A process of producing a carbonized fiber which, during oxidation, is drawn beyond the prior limit of elongation of about 95%, said process comprising the steps of:
a. supplying an oxygen-containing atmosphere to a multizone gradient furnace;
b. heating said furnace so as to maintain a temperature gradient in said atmosphere from about 220°C
at the inlet of said furnace to about 260°C at the outlet thereof;
c. permeating a multifilament tow of fibers formed of a polyacrylonitrile copolymer which contains about 85 mole percent acrylonitrile units and about 15 mole percent methyl acrylate, with sufficient carboxylic acid to permit subsequent drawing of said fibers during oxidation to at least double its original length;
d. passing the multifilament permeated tow of fibers through said atmosphere along said temperature gradient in said furnace, with a residence time of between about 2 and 120 minutes;
e. tensioning said multifilament permeated tow of fibers during passage through said atmosphere along said temperature gradient so as to draw the fibers to at least double its original length; and f. thereafter passing the multifilament tow through a second multizone gradient furnace with a temperature gradient of about 300°C at the inlet thereof to about 800°C at the outlet thereof.
a. supplying an oxygen-containing atmosphere to a multizone gradient furnace;
b. heating said furnace so as to maintain a temperature gradient in said atmosphere from about 220°C
at the inlet of said furnace to about 260°C at the outlet thereof;
c. permeating a multifilament tow of fibers formed of a polyacrylonitrile copolymer which contains about 85 mole percent acrylonitrile units and about 15 mole percent methyl acrylate, with sufficient carboxylic acid to permit subsequent drawing of said fibers during oxidation to at least double its original length;
d. passing the multifilament permeated tow of fibers through said atmosphere along said temperature gradient in said furnace, with a residence time of between about 2 and 120 minutes;
e. tensioning said multifilament permeated tow of fibers during passage through said atmosphere along said temperature gradient so as to draw the fibers to at least double its original length; and f. thereafter passing the multifilament tow through a second multizone gradient furnace with a temperature gradient of about 300°C at the inlet thereof to about 800°C at the outlet thereof.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US19312080A | 1980-10-02 | 1980-10-02 | |
| US06/193,120 | 1980-10-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1156409A true CA1156409A (en) | 1983-11-08 |
Family
ID=22712348
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376727A Expired CA1156409A (en) | 1980-10-02 | 1981-05-01 | Method of producing carbon fiber and product thereof |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5766122A (en) |
| CA (1) | CA1156409A (en) |
| DE (1) | DE3138893A1 (en) |
| FR (1) | FR2491504B1 (en) |
| GB (1) | GB2084975B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4507272A (en) * | 1983-05-09 | 1985-03-26 | Hitco | Method of purifying partially carbonized pan material prior to carbonization |
| HU196271B (en) * | 1983-12-05 | 1988-11-28 | Dow Chemical Co | Electrode for secondary electric energy storing device and secondary electric energy storing device |
| JPS60137811A (en) * | 1983-12-22 | 1985-07-22 | Toho Rayon Co Ltd | Active carbon fiber for cleaning water |
| EP0154175A3 (en) * | 1984-03-07 | 1989-05-03 | American Cyanamid Company | Rapid stabilization process for carbon fiber precursors |
| JPS61152826A (en) * | 1984-12-24 | 1986-07-11 | Mitsubishi Rayon Co Ltd | High-elasticity carbon fiber and its production |
| US4776995A (en) * | 1985-03-22 | 1988-10-11 | Fiber Materials, Inc. | Method of making a structure |
| CN108431310A (en) | 2015-12-31 | 2018-08-21 | Ut-巴特勒有限公司 | The method for producing carbon fiber from multipurpose commercial fibres |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3708326A (en) * | 1971-01-25 | 1973-01-02 | Celanese Corp | Stabilization of acrylic fibers and films |
| JPS5029530B2 (en) * | 1971-08-11 | 1975-09-23 | ||
| JPS5221425A (en) * | 1975-08-11 | 1977-02-18 | Asahi Chem Ind Co Ltd | Process for manufacturing carbon fibers |
| US4100004A (en) * | 1976-05-11 | 1978-07-11 | Securicum S.A. | Method of making carbon fibers and resin-impregnated carbon fibers |
-
1981
- 1981-05-01 CA CA000376727A patent/CA1156409A/en not_active Expired
- 1981-05-08 GB GB8114160A patent/GB2084975B/en not_active Expired
- 1981-07-13 JP JP10918981A patent/JPS5766122A/en active Granted
- 1981-09-30 DE DE19813138893 patent/DE3138893A1/en active Granted
- 1981-09-30 FR FR8118495A patent/FR2491504B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3138893C2 (en) | 1992-03-19 |
| GB2084975A (en) | 1982-04-21 |
| GB2084975B (en) | 1985-08-21 |
| FR2491504A1 (en) | 1982-04-09 |
| JPH0229766B2 (en) | 1990-07-02 |
| DE3138893A1 (en) | 1982-06-24 |
| FR2491504B1 (en) | 1985-08-23 |
| JPS5766122A (en) | 1982-04-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1095206A (en) | Process for producing carbon fibers | |
| US3539295A (en) | Thermal stabilization and carbonization of acrylic fibrous materials | |
| US4671950A (en) | High-strength carbonaceous fiber | |
| US10961642B2 (en) | Method of producing carbon fibers from multipurpose commercial fibers | |
| US4080417A (en) | Process for producing carbon fibers having excellent properties | |
| JPS6052208B2 (en) | Carbon fiber tow manufacturing method | |
| US3775520A (en) | Carbonization/graphitization of poly-acrylonitrile fibers containing residual spinning solvent | |
| WO2000005440A1 (en) | Acrylonitril-based precursor fiber for carbon fiber and method for production thereof | |
| US20150118142A1 (en) | Formation of carbon nanotube-enhanced fibers and carbon nanotube-enahnced hybrid structures | |
| US3723607A (en) | Surface modification of carbon fibers | |
| US4526770A (en) | Method of producing carbon fiber and product thereof | |
| US4536448A (en) | Preoxidized fiber and process for producing the same | |
| KR870000533B1 (en) | Carbon fiber's making method | |
| CA1156409A (en) | Method of producing carbon fiber and product thereof | |
| US4002426A (en) | Production of stabilized non-burning acrylic fibers and films | |
| US5066433A (en) | Method of manufacturing carbon fiber using preliminary stretch | |
| EP0147005A2 (en) | Oxidation of pitch fibers | |
| US3723150A (en) | Surface modification of carbon fibers | |
| US3592595A (en) | Stabilization and carbonization of acrylic fibrous material | |
| US3954950A (en) | Production of high tenacity graphitic fibrous materials | |
| US3708326A (en) | Stabilization of acrylic fibers and films | |
| US4452601A (en) | Process for the thermal stabilization of acrylic fibers and films | |
| JPH02242920A (en) | Carbon fiber containing composite metal | |
| US3820951A (en) | Process for the thermal stabilization of polyacrylonitrile fibers andfilms | |
| US3900556A (en) | Process for the continuous carbonization and graphitization of a stabilized acrylic fibrous material |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |