CA1040370A - Process for producing carbon fibers having excellent physical properties - Google Patents
Process for producing carbon fibers having excellent physical propertiesInfo
- Publication number
- CA1040370A CA1040370A CA219,386A CA219386A CA1040370A CA 1040370 A CA1040370 A CA 1040370A CA 219386 A CA219386 A CA 219386A CA 1040370 A CA1040370 A CA 1040370A
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- Canada
- Prior art keywords
- fibers
- mol
- acrylonitrile
- acid
- acrylonitrile copolymer
- Prior art date
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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 carbon fibers having excellent physical properties, very high tensile strengths and high moduli of elasticity are prepared from acrylonitrile copolymer fibers, produced by copolymerizing at least 80 mol % acrylonitrile with an unsaturated monomer containing a carboxyl group in which 0.1 to 15% of the terminal hydrogens have been replaced with an alkali metal cation or ammonium ion, by heating said fibers in a first thermal stabilization stage, further heating said fibers in a second, carbonizing stage and, if desired, further heating said fibers in a third, graphitizing stage.
Description
104~370 This invention relates to an improved process for pro-ducing carbon fibers (including graphite fiber~) from acryloni-trilic fibers and more particularly to a process for industrially advantageously producing carbon fibers having a very high tensile strength and modulus of elasticity, w~-thin a short firing or heating time, by heating acrylonitrile copolymer fibers, wherein a ~pecific amount of carboxyl groups contained in the copolymer has been converted to the form of a salt (i.e. -COOX wherein X
is an alkali metal cation or ammonium ion).
It is known that carbon fibers useful as reinforcing materials, exothermic elements and heat-resistant materials are obtained by heating acrylonitrilic fibers to 200 to 400C. in an oxidizing atmosphere 80 as to cyclize or peroxidize the acrylonitrile fibers and then heating them to a high temperature (usually above 800C.) in a non-oxidizing atmosphere.
However, the first step of heating the acrylonitrilic fibers in an oxidizing atmosphere to form a cyclized structure of the polynaphtyridine ring in the fibers, or the so-called thermal stabilization step, is a very important step influencing the physical properties of the resulting ~arbon fibers which are the final products. It has been considered that this first step re~uires a long heating period and therefore efficiency of the production of the carbon fibers has heretofore been low.
When the thermal-stabilization step is conducted at a high temperature, or when the fibers are heated at a very fast rate of rise of temperature, such guick reactions as intermole-cular cross-linking and intramolecular cyclization occur at temperatures near the exothermic transition point of the fibers, resulting in a local heat regeneration, with nonuniform reac-.,~' ~ ' ' .
^: . , . . , , . ; ;
.
104~370 tions that cause the formation of a pitch or tarry substance,resulting from the fusion of the fibers into one another, and adversely affecting the physical properties of the carbon fibers.
various methods have been suggested to promo~e such cyclizing reactions in order to obtain thermally stabilized fibers within a short time. These include methods wherein a special comonomer component is introduced into the fiber forming polymer, or wherein a special or detrimental chemical treatment is employed, or wherein a complicated thermal-stabilization treatment is used. These methods have not always contributed to the improvement of the economy and industrial productivity of carbon fibers. Among these, the method wherein acrylonitrile copolymer fibers, prepared by copolymerizing acrylonitrile with an unsaturated monomer containing a carboxyl group, are used as precursors is advantageous in respect of the reduction of the firing or heat treatment time because, when such comonomer component is introduced, the exothermic ~ransition point of the fibers will be reduced and, when heated, the fibers will become easily condensed and cyclized. HOwever, the resulting carbon fibers do not have a quality suitable for the desired uses.
We have found that, when acrylonitrile copolymer fibers, in which a specific amount of carboxyl groups are contained in the fiber-forming polymer in the form of a sa~t represented by -COOX (wherein X is an alkali metal cation or ammonium ion), are used as precursors and are fired or heated, the firing (or heating) time can be remarkably reduced, and carbon fibers 104~370 of a very high strength and modulus of elasticity can be industrially produced.
Therefore the principal object of the present invention is to industrially advantageously obtain carbon fibers having excellent physical properties.
Another object of the present invention is to obtain carbon fibers of a high strength and high modulus of elasticity within a short heating time.
Another object of the present invention is to obtain carbon fibers with excellent properties (including high flexi-bility) by using acrylonitrile copolymer fiber~ containing carboxyl groups, and a specific amount of their salts, a~ pre-cursors 80 that a quick and uniform thermal-stabilization can be effected without fusion of the fibers into one another.
Other object~ of the present invention will become apparent from the following description.
The above mentioned objects of the present invention can be attained by firing or heating acrylonitrile copolymer fibers made of an acrylonitrile copolymer, prepared by copoly-merizing acrylonitrile with 0.3 to 6 mol % of an unsaturatedmonomer containing a carboxyl group and in which 0.1 to 15% of the terminal hydrogens of said carboxyl group~ are replaced with an alkali metal cation or ammonium ion, and then by carbonizing and/or graphitizing the said acrylonitrile copolymer fibers in the usual manner.
Thu~ the novel and important feature of the present invention is in the use, as precursors, of acrylonitrile co-polymer fibers in which both carboxyl groups (-COOH) and their salt form (-COOX) are contained, wherein the content of said _ 3 _ ' , ' 104~370 salt (--COOX) is 0.1 to 15 mol ~, or preferably 0.5 to 10 mol ~, of the total amount of the carboxyl groups (-COOH) and salts (-COOX). The cyclizing reaction or cross-linking reaction caused in the thermal-stabilization step is thus accelerated and made to proceed more uniformly. Therefore the thermal-stabilization step can be conducted at a high temperature, or a quick temperature elevating operation may be adopted, with the result that the heating or firing time can be shortened, the formation of impurities such as pitch and tarry substance in the firing or heating process may be prevented, and there-fore carbon fibers having a remarkably improved strength and modulus of elasticity, uniform in quality and having excellent physical properties can be produced.
The acrylonitrile copolymer fiber3 to be used in the pre~ent invention are those produced by conventional spinning proces~es ~uch as, for example, a wet-spinning process, a dry-spinning process or a dry/wet-spinning process, from an acrylonitrile copolymer containing at least 80 mol %, or preferably more than 90 mol %, of acrylonitrile and copolymer-ized with 0.3 to 6 mol ~ or preferably 0.5 to 3 mol % of an unsaturated monomer containing a carboxyl group. When the cont-ent of the copolymerized unsaturated monomer containing carboxyl group is le~s than 0.3 mol %, the desired effects of this invention i.e. shortening of the heat treatment time and improvement of the physical properties of the resulting carbon fibers, will not be readily attainable. When the content exceeds 6 mol %, it will be difficult to produce fibers having suitable physical properties for use as precursors for the , ~
:~, production of carbon fibers, and further no ~ufficient improvement in the physical properties in the resulting carbon fibers is seen.
Examples of carboxyl group-containing unsaturated monomers suitable for copolymerization with acrylonitrile, are acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, ,; isocrotonic acid, itaconic acid, maleic acid, mesaconic acid, citraconic acid and their water-soluble salts (alkali metal salts and ammonium salts). Acrylonitrile copolymer fibers, containing a specific amount of carboxyl groups and their salts, to be used in the present invention may be produced by forming fibers from a copolymer obtained by copolymerizing acrylonitrile with a mixture of the above mentioned unsaturated caxboxylic acid and unsaturated carboxylic acid salt at proper proportions.
If de~ired, 0 to 14 mol ~ of any other unsaturated monomer can be copolymerized with the acrylonitrile and carboxyl group-containing unsaturated monomer. Examples of such other unsaturated monomers are such well known ethylenically unsat-urated compounds as alkyl alcohol, methallyl alcohol ~-hydroxy-propyl acrylonitrile, methacrylonitrile, a-methyleneglutaro-nitrile, isopropenyl acetate, acrylamide, dimethylaminoethyl methacrylate, vinylpyridine, vinylpyrrolidone, methyl acrylate, methyl methacrylate, vinyl acetate, acryl chloride, ~odium methallylsulfonate and potassium p-styrenesulfonate.
Further, the acrylonitrile copolymer may be produced by such well known polymerization systems as solution polymeri-zation systems, bulk polymerization systems, emulsion polymeri-zation systems or suspension polymerization systems. Suitable ~ 5 --~.. , . , . . . ~ .
-` 104~370, solvents for producing acrylonitrile copolymer fibers from such copolymers are organic solvents such as dimethylformamide, dimethylacetamide and dimethyl sulfoxide and inorganic solvents such as aqueous solutions of nitric acid, zinc chloride and thiocyanate.
The copolymer may be spun into fibers in ordinary and well known manners.
Any suitable method may be used for obtaining the specific predetermined amount of carboxyl salts (-COOX) desired in the acrylonitrile copolymer fibers. For example, when using an acrylonitrile copolymer copolymerized with an unsaturated carboxylic acid, there may be employed a method wherein said copolymer or the fiber obtained from said copolymer is treated with an aqueous solution containing an alkali metal cation or an ammonium ion. When an acrylonitrile copolymer copolymerized with an alkali metal salt or ammonium salt of an unsaturated carboxylic acid is used there may be employed a method wherein said copolymer or the fiber obtained from said copolymer i8 treated with an acid aqueous solution. It is also possible, as already mentioned, to employ a method wherein the ratio of carboxyl groups and salts thereof in the fiber i8 adjusted by properly mixing the unsaturated carboxylic acid and the unsaturated carboxylic acid salt for the copolymerization with acrylonitrile. Regardless of the method used, any acrylonitrile copolymer fibers in which 0.1 to 15% of terminal hydrogens of carboxyl groups (-COOH) in the fibers is replaced with an alkali metal cation or ammonium ion may be used in this invention. A preferred process for producing the fibers to be used in the present invention is the process wherein gel fibers, ~040370 in a water-swollen state, obtained ~y spinning an acrylonitrile copolymer copol~merized with an unsaturated carboxylic acid are treated with an aqueous solution containing an alkali metal cation or ammonium iGn so that a part of the carboxyl group (-COOH) in said fibers is converted to the salt form (-COOX).
In this case, the treating condition may vary noticeably depending upon the kind of the solventbD be used to form the fibers, the kind of the cation and the oriented state of the gel fibers. In any event, it is necessary that the acrylonitrile copolymer fibers to be used in the present invention should be those wherein 0.1 to 15 mol %, or preferably 0.5 to 10 mol %, of the carboxyl groups contained in said fibers is in the form of a salt (-COOX).
In producing carbon fibers from the thus obtained ; acrylonitrile copolymer fibers containing carboxyl groups (-COOH) and salts thereof (-C~OX) at specific or predetermined proportions there can be employed any known conventional processes. However, it is generally preferred to employ a firing or heating process which comprises a primary firing step (so-called thermal stabilization step) wherein the fibers are heated to between 150 and 400C. in an oxidizing atmosphere to effect the cyclization ta cyclized structure of a polynaphtyridine ring is formed in the fiber) and a secondary firing step wherein the fibers are then heated at a high temperature (usually above 800C.) in a non-oxidizing atmosphere or under a reduced pressure 80 as to be carbonized, or carbonized and graphitized.
For the thermal-stabilization step air is preferred as the atmosphere, but there can be used other processes wherein the fibers are thermally stabilized in the presence of sulfur dioxide .... . . .
,: . . . . .
or nitrogen monoxide gas, or under the radiation of rays. The carbonization is conducted generally at a temperature of from ~oO to 2000c. In order to further graphitize the carbon fiber~
thus obtained, the fibers are heated generally to a temperature of from 2000 to 3500C. The carbonizing or graphitizing is preferably carried out in an atmosphere of nitrogen, hydrogen, helium or argon. Further, for the production of carbon fibers of a higher strength and higher modulus of elasticity, it is preferred to conduct the heating under tension. It is particularly effective to apply tension at the time of conducting the thermal-stabilization and also at the time of carbonizing or graphitizing the fibers. The carbonization or graphitization may be carried out under a reduced or increased pressure.
According to the present invention, it is possible to ; produce carbon fibers having excellent strength and modulus of elasticity, and these carbon fibers can be used, for example, as reinforcing materials, heating elements and heat-resistant materials.
The invention will be further explained by means of the following Examples, in which the percentages and parts are by weight unless otherwise specified.
Exam~le 1 Twelve parts of an acrylonitrile copolymer consisting of 98 mol % acrylonitrile and 2 mol % methacrylic acid and obtained by an aqueous suspension polymerization process using (NH4)2S20g/
Na2S03 as a redox catalyst were dissolved in 88 parts of a 46%
aqueous solution of sodium thiocyanate to prepare a spinning solution. The spinning solution was extruded into a ' ' ' ' ' ~6~4~370 coagulating bath consisting of a 12% aqueous solution of sodium-thiocyanate, at -3c. and adjusted to pH 4 by H2SO4, through a spinnerette of 50 orifices (orifice diameter 0.06 mm.). The content of Na2SO4 in the coagulating bath was varied. Then the obtained gel fibers were well washed with water, then stretched 5 times their original length in boiling water, and further ~ stre~
stretched twice their length in superheated steam, and were then dried to obtain acrylonitrile copolymer fibers of a strength of 6.2 g./d. and Young's modulus of 89 g./d.
The thus obtained various acrylonitrile copolymer fibers resulting from different Na2S04 concentrations in the coagulating bath were respectively heated to obtain four kinds of carbon fibers. The fibers were heated by continuously elevating the temperature for 20 minutes from 200C. to 300C. in an air atmosphere with an electric furnace to obtain thermal-stabilized fibers. These thermally stabilized fibers were then carbonized by continuously elevating the temperature for lO0 minutes to 1200C. in a nitrogen gas atmosphere.
The strengths and moduli of elasticity of the four kind~
of carbon fiber~ thus obtained were measured. The results are shown in Table l. As is apparent from Table 1, according to the present invention, the strength and the modulus of elasticity of carbon fibers can be remarkably improved.
on the other hand, when fibers made from an acrylonitrile copolymer copolymerized with 2 mol % methyl acrylate were heated in the same manner as mentioned above, the fibers noticeably fused together and the carbon fibers so obtained were so brittle that their physical properties could not be measured.
~,.. . .. .. .. .. .. . . .
., .- . :,, ., . - -: .. , .: ~ ; , , ~040370 Table 1 Acrylonitrile copolymer fibers carbon fibers Na2S04 con- Modulus of No. centration Na con- strength* elasticity in coagulat- version (kg,/mm2) (tons/mm2) ing bath rate (%) (mol o/O) 1 0 9.7 258 24
is an alkali metal cation or ammonium ion).
It is known that carbon fibers useful as reinforcing materials, exothermic elements and heat-resistant materials are obtained by heating acrylonitrilic fibers to 200 to 400C. in an oxidizing atmosphere 80 as to cyclize or peroxidize the acrylonitrile fibers and then heating them to a high temperature (usually above 800C.) in a non-oxidizing atmosphere.
However, the first step of heating the acrylonitrilic fibers in an oxidizing atmosphere to form a cyclized structure of the polynaphtyridine ring in the fibers, or the so-called thermal stabilization step, is a very important step influencing the physical properties of the resulting ~arbon fibers which are the final products. It has been considered that this first step re~uires a long heating period and therefore efficiency of the production of the carbon fibers has heretofore been low.
When the thermal-stabilization step is conducted at a high temperature, or when the fibers are heated at a very fast rate of rise of temperature, such guick reactions as intermole-cular cross-linking and intramolecular cyclization occur at temperatures near the exothermic transition point of the fibers, resulting in a local heat regeneration, with nonuniform reac-.,~' ~ ' ' .
^: . , . . , , . ; ;
.
104~370 tions that cause the formation of a pitch or tarry substance,resulting from the fusion of the fibers into one another, and adversely affecting the physical properties of the carbon fibers.
various methods have been suggested to promo~e such cyclizing reactions in order to obtain thermally stabilized fibers within a short time. These include methods wherein a special comonomer component is introduced into the fiber forming polymer, or wherein a special or detrimental chemical treatment is employed, or wherein a complicated thermal-stabilization treatment is used. These methods have not always contributed to the improvement of the economy and industrial productivity of carbon fibers. Among these, the method wherein acrylonitrile copolymer fibers, prepared by copolymerizing acrylonitrile with an unsaturated monomer containing a carboxyl group, are used as precursors is advantageous in respect of the reduction of the firing or heat treatment time because, when such comonomer component is introduced, the exothermic ~ransition point of the fibers will be reduced and, when heated, the fibers will become easily condensed and cyclized. HOwever, the resulting carbon fibers do not have a quality suitable for the desired uses.
We have found that, when acrylonitrile copolymer fibers, in which a specific amount of carboxyl groups are contained in the fiber-forming polymer in the form of a sa~t represented by -COOX (wherein X is an alkali metal cation or ammonium ion), are used as precursors and are fired or heated, the firing (or heating) time can be remarkably reduced, and carbon fibers 104~370 of a very high strength and modulus of elasticity can be industrially produced.
Therefore the principal object of the present invention is to industrially advantageously obtain carbon fibers having excellent physical properties.
Another object of the present invention is to obtain carbon fibers of a high strength and high modulus of elasticity within a short heating time.
Another object of the present invention is to obtain carbon fibers with excellent properties (including high flexi-bility) by using acrylonitrile copolymer fiber~ containing carboxyl groups, and a specific amount of their salts, a~ pre-cursors 80 that a quick and uniform thermal-stabilization can be effected without fusion of the fibers into one another.
Other object~ of the present invention will become apparent from the following description.
The above mentioned objects of the present invention can be attained by firing or heating acrylonitrile copolymer fibers made of an acrylonitrile copolymer, prepared by copoly-merizing acrylonitrile with 0.3 to 6 mol % of an unsaturatedmonomer containing a carboxyl group and in which 0.1 to 15% of the terminal hydrogens of said carboxyl group~ are replaced with an alkali metal cation or ammonium ion, and then by carbonizing and/or graphitizing the said acrylonitrile copolymer fibers in the usual manner.
Thu~ the novel and important feature of the present invention is in the use, as precursors, of acrylonitrile co-polymer fibers in which both carboxyl groups (-COOH) and their salt form (-COOX) are contained, wherein the content of said _ 3 _ ' , ' 104~370 salt (--COOX) is 0.1 to 15 mol ~, or preferably 0.5 to 10 mol ~, of the total amount of the carboxyl groups (-COOH) and salts (-COOX). The cyclizing reaction or cross-linking reaction caused in the thermal-stabilization step is thus accelerated and made to proceed more uniformly. Therefore the thermal-stabilization step can be conducted at a high temperature, or a quick temperature elevating operation may be adopted, with the result that the heating or firing time can be shortened, the formation of impurities such as pitch and tarry substance in the firing or heating process may be prevented, and there-fore carbon fibers having a remarkably improved strength and modulus of elasticity, uniform in quality and having excellent physical properties can be produced.
The acrylonitrile copolymer fiber3 to be used in the pre~ent invention are those produced by conventional spinning proces~es ~uch as, for example, a wet-spinning process, a dry-spinning process or a dry/wet-spinning process, from an acrylonitrile copolymer containing at least 80 mol %, or preferably more than 90 mol %, of acrylonitrile and copolymer-ized with 0.3 to 6 mol ~ or preferably 0.5 to 3 mol % of an unsaturated monomer containing a carboxyl group. When the cont-ent of the copolymerized unsaturated monomer containing carboxyl group is le~s than 0.3 mol %, the desired effects of this invention i.e. shortening of the heat treatment time and improvement of the physical properties of the resulting carbon fibers, will not be readily attainable. When the content exceeds 6 mol %, it will be difficult to produce fibers having suitable physical properties for use as precursors for the , ~
:~, production of carbon fibers, and further no ~ufficient improvement in the physical properties in the resulting carbon fibers is seen.
Examples of carboxyl group-containing unsaturated monomers suitable for copolymerization with acrylonitrile, are acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, ,; isocrotonic acid, itaconic acid, maleic acid, mesaconic acid, citraconic acid and their water-soluble salts (alkali metal salts and ammonium salts). Acrylonitrile copolymer fibers, containing a specific amount of carboxyl groups and their salts, to be used in the present invention may be produced by forming fibers from a copolymer obtained by copolymerizing acrylonitrile with a mixture of the above mentioned unsaturated caxboxylic acid and unsaturated carboxylic acid salt at proper proportions.
If de~ired, 0 to 14 mol ~ of any other unsaturated monomer can be copolymerized with the acrylonitrile and carboxyl group-containing unsaturated monomer. Examples of such other unsaturated monomers are such well known ethylenically unsat-urated compounds as alkyl alcohol, methallyl alcohol ~-hydroxy-propyl acrylonitrile, methacrylonitrile, a-methyleneglutaro-nitrile, isopropenyl acetate, acrylamide, dimethylaminoethyl methacrylate, vinylpyridine, vinylpyrrolidone, methyl acrylate, methyl methacrylate, vinyl acetate, acryl chloride, ~odium methallylsulfonate and potassium p-styrenesulfonate.
Further, the acrylonitrile copolymer may be produced by such well known polymerization systems as solution polymeri-zation systems, bulk polymerization systems, emulsion polymeri-zation systems or suspension polymerization systems. Suitable ~ 5 --~.. , . , . . . ~ .
-` 104~370, solvents for producing acrylonitrile copolymer fibers from such copolymers are organic solvents such as dimethylformamide, dimethylacetamide and dimethyl sulfoxide and inorganic solvents such as aqueous solutions of nitric acid, zinc chloride and thiocyanate.
The copolymer may be spun into fibers in ordinary and well known manners.
Any suitable method may be used for obtaining the specific predetermined amount of carboxyl salts (-COOX) desired in the acrylonitrile copolymer fibers. For example, when using an acrylonitrile copolymer copolymerized with an unsaturated carboxylic acid, there may be employed a method wherein said copolymer or the fiber obtained from said copolymer is treated with an aqueous solution containing an alkali metal cation or an ammonium ion. When an acrylonitrile copolymer copolymerized with an alkali metal salt or ammonium salt of an unsaturated carboxylic acid is used there may be employed a method wherein said copolymer or the fiber obtained from said copolymer i8 treated with an acid aqueous solution. It is also possible, as already mentioned, to employ a method wherein the ratio of carboxyl groups and salts thereof in the fiber i8 adjusted by properly mixing the unsaturated carboxylic acid and the unsaturated carboxylic acid salt for the copolymerization with acrylonitrile. Regardless of the method used, any acrylonitrile copolymer fibers in which 0.1 to 15% of terminal hydrogens of carboxyl groups (-COOH) in the fibers is replaced with an alkali metal cation or ammonium ion may be used in this invention. A preferred process for producing the fibers to be used in the present invention is the process wherein gel fibers, ~040370 in a water-swollen state, obtained ~y spinning an acrylonitrile copolymer copol~merized with an unsaturated carboxylic acid are treated with an aqueous solution containing an alkali metal cation or ammonium iGn so that a part of the carboxyl group (-COOH) in said fibers is converted to the salt form (-COOX).
In this case, the treating condition may vary noticeably depending upon the kind of the solventbD be used to form the fibers, the kind of the cation and the oriented state of the gel fibers. In any event, it is necessary that the acrylonitrile copolymer fibers to be used in the present invention should be those wherein 0.1 to 15 mol %, or preferably 0.5 to 10 mol %, of the carboxyl groups contained in said fibers is in the form of a salt (-COOX).
In producing carbon fibers from the thus obtained ; acrylonitrile copolymer fibers containing carboxyl groups (-COOH) and salts thereof (-C~OX) at specific or predetermined proportions there can be employed any known conventional processes. However, it is generally preferred to employ a firing or heating process which comprises a primary firing step (so-called thermal stabilization step) wherein the fibers are heated to between 150 and 400C. in an oxidizing atmosphere to effect the cyclization ta cyclized structure of a polynaphtyridine ring is formed in the fiber) and a secondary firing step wherein the fibers are then heated at a high temperature (usually above 800C.) in a non-oxidizing atmosphere or under a reduced pressure 80 as to be carbonized, or carbonized and graphitized.
For the thermal-stabilization step air is preferred as the atmosphere, but there can be used other processes wherein the fibers are thermally stabilized in the presence of sulfur dioxide .... . . .
,: . . . . .
or nitrogen monoxide gas, or under the radiation of rays. The carbonization is conducted generally at a temperature of from ~oO to 2000c. In order to further graphitize the carbon fiber~
thus obtained, the fibers are heated generally to a temperature of from 2000 to 3500C. The carbonizing or graphitizing is preferably carried out in an atmosphere of nitrogen, hydrogen, helium or argon. Further, for the production of carbon fibers of a higher strength and higher modulus of elasticity, it is preferred to conduct the heating under tension. It is particularly effective to apply tension at the time of conducting the thermal-stabilization and also at the time of carbonizing or graphitizing the fibers. The carbonization or graphitization may be carried out under a reduced or increased pressure.
According to the present invention, it is possible to ; produce carbon fibers having excellent strength and modulus of elasticity, and these carbon fibers can be used, for example, as reinforcing materials, heating elements and heat-resistant materials.
The invention will be further explained by means of the following Examples, in which the percentages and parts are by weight unless otherwise specified.
Exam~le 1 Twelve parts of an acrylonitrile copolymer consisting of 98 mol % acrylonitrile and 2 mol % methacrylic acid and obtained by an aqueous suspension polymerization process using (NH4)2S20g/
Na2S03 as a redox catalyst were dissolved in 88 parts of a 46%
aqueous solution of sodium thiocyanate to prepare a spinning solution. The spinning solution was extruded into a ' ' ' ' ' ~6~4~370 coagulating bath consisting of a 12% aqueous solution of sodium-thiocyanate, at -3c. and adjusted to pH 4 by H2SO4, through a spinnerette of 50 orifices (orifice diameter 0.06 mm.). The content of Na2SO4 in the coagulating bath was varied. Then the obtained gel fibers were well washed with water, then stretched 5 times their original length in boiling water, and further ~ stre~
stretched twice their length in superheated steam, and were then dried to obtain acrylonitrile copolymer fibers of a strength of 6.2 g./d. and Young's modulus of 89 g./d.
The thus obtained various acrylonitrile copolymer fibers resulting from different Na2S04 concentrations in the coagulating bath were respectively heated to obtain four kinds of carbon fibers. The fibers were heated by continuously elevating the temperature for 20 minutes from 200C. to 300C. in an air atmosphere with an electric furnace to obtain thermal-stabilized fibers. These thermally stabilized fibers were then carbonized by continuously elevating the temperature for lO0 minutes to 1200C. in a nitrogen gas atmosphere.
The strengths and moduli of elasticity of the four kind~
of carbon fiber~ thus obtained were measured. The results are shown in Table l. As is apparent from Table 1, according to the present invention, the strength and the modulus of elasticity of carbon fibers can be remarkably improved.
on the other hand, when fibers made from an acrylonitrile copolymer copolymerized with 2 mol % methyl acrylate were heated in the same manner as mentioned above, the fibers noticeably fused together and the carbon fibers so obtained were so brittle that their physical properties could not be measured.
~,.. . .. .. .. .. .. . . .
., .- . :,, ., . - -: .. , .: ~ ; , , ~040370 Table 1 Acrylonitrile copolymer fibers carbon fibers Na2S04 con- Modulus of No. centration Na con- strength* elasticity in coagulat- version (kg,/mm2) (tons/mm2) ing bath rate (%) (mol o/O) 1 0 9.7 258 24
2 0.1 14.1 237 22
3 1.0 40.1 183 14
4 5.0 56.5 166 13 * The rate of the conversion of the carboxyl groups (-COOH) in the fibers to the salt form (-COONa).
Example 2 A spinning solution obtained by dissolving 12 parts of an acrylonitrile copolymer consisting of 97 mol % acrylonitrile, 2 mol % acrylic acid and 1 mol % methyl acrylate in 88 parts of a 46% aqueous solution of sodium thiocyanate was extruded into a 12% aqueous solution of sodium thiocyanate at -3C.
through a spinnerette. The thus obtained gel fibers were then well washed with water and were then treated with an aqueous solution of hydrochloric acid of various concentrations. The thus treated gel fibers were then stretched and dried in the same manner as that of Example 1 to obtain acrylonitrile co-polymer fibers of a strength of 6.1 g./d. and Young's modulus of 87 g./d.
The thus obtained various fibers (different in the Na con-version rate of the carboxyl group terminal hydrogen) were fired or heated under the same conditions as in Example 1 to obtain four kinds of carbon fibers. The physical properties of 10~ 70 such carbon fibers are shown in Table 2. It is apparent therefrom that the physical properties of carbon fibers can be remarkably improved by converting a certain amount of carboxyl groups in acrylonitrile copolymer fibers to their salt form (-COOX), according to the present invention.
Table 2 Acrylonitrile copolymer fibers Carbon fibers ..
Acid Na conversionStrength Modulus of ; 10No. treatment elasticity (pH) (mol %)(kg./mm2) (tons/mm2) . _ . . _ _ _ . .
2 2 2 . 3 265 24 3 3 13 . 1 227 23 4 5 26. 8 164 14 Examp~
A spinning solution obtained by dissolving 18 parts of an acrylonitrile copolymer consisting of 96 mol % acrylonitrile and 4 mol % methacrylic acid in 82 parts of dimethyl-formamide 20 was wet-spun into a 60% aqueous solution of dimethylformamide through a spinnerette. The gel fibers thus obtained were well washed with water, then treated with an al~aline aqueous solution (25C~ ) set at various pH values by using KOH. The fibers were stretched 3. 5 times their original length in hot to s~t~4c~
water, and further stretched~twice their length in superheated steam and were then dried to obtain acrylonitrile copolymer fibers having had various salt form (-COOK) conversion rates.
The fibers thus obtained were then respectively fed into an electric furnace of an effective length of 106 cm. having a 1~4(~ 0 continuous temperature gradient from 200C. to 305C. The fibers were passed through the furnace continuously at a velocity of 6 cm./min., and were subjected to primary firing in an air atmosphere and were then continuously carbonized in a nitrogen gas atmosphere, using the same furnace at a temperature from 300C. to 1200C.
The strengths and moduli of elasticity of the thus obtained various carbon fibers were measured. The results are shown in Table 3. It will be observed from Table 3 that, by converting a certain amount of carboxyl groups in acrylonitrile copolymer fibers to the salt form (-COOK), the physical properties of the obtained fibers are improved.
Table 3 Acrylonitrile copolymer fibers Carbon fibers .
pH of alkaline K conversionStrength Modulus of No. aqueous rate elasticity ~olution (mol %)(kg./mm2) (tons/mm2) 20 2 8 2.1 256 22 3 9 4.1 249 22 4 10 5.9 260 23 ~ 12 -. . . .
. - :
Example 2 A spinning solution obtained by dissolving 12 parts of an acrylonitrile copolymer consisting of 97 mol % acrylonitrile, 2 mol % acrylic acid and 1 mol % methyl acrylate in 88 parts of a 46% aqueous solution of sodium thiocyanate was extruded into a 12% aqueous solution of sodium thiocyanate at -3C.
through a spinnerette. The thus obtained gel fibers were then well washed with water and were then treated with an aqueous solution of hydrochloric acid of various concentrations. The thus treated gel fibers were then stretched and dried in the same manner as that of Example 1 to obtain acrylonitrile co-polymer fibers of a strength of 6.1 g./d. and Young's modulus of 87 g./d.
The thus obtained various fibers (different in the Na con-version rate of the carboxyl group terminal hydrogen) were fired or heated under the same conditions as in Example 1 to obtain four kinds of carbon fibers. The physical properties of 10~ 70 such carbon fibers are shown in Table 2. It is apparent therefrom that the physical properties of carbon fibers can be remarkably improved by converting a certain amount of carboxyl groups in acrylonitrile copolymer fibers to their salt form (-COOX), according to the present invention.
Table 2 Acrylonitrile copolymer fibers Carbon fibers ..
Acid Na conversionStrength Modulus of ; 10No. treatment elasticity (pH) (mol %)(kg./mm2) (tons/mm2) . _ . . _ _ _ . .
2 2 2 . 3 265 24 3 3 13 . 1 227 23 4 5 26. 8 164 14 Examp~
A spinning solution obtained by dissolving 18 parts of an acrylonitrile copolymer consisting of 96 mol % acrylonitrile and 4 mol % methacrylic acid in 82 parts of dimethyl-formamide 20 was wet-spun into a 60% aqueous solution of dimethylformamide through a spinnerette. The gel fibers thus obtained were well washed with water, then treated with an al~aline aqueous solution (25C~ ) set at various pH values by using KOH. The fibers were stretched 3. 5 times their original length in hot to s~t~4c~
water, and further stretched~twice their length in superheated steam and were then dried to obtain acrylonitrile copolymer fibers having had various salt form (-COOK) conversion rates.
The fibers thus obtained were then respectively fed into an electric furnace of an effective length of 106 cm. having a 1~4(~ 0 continuous temperature gradient from 200C. to 305C. The fibers were passed through the furnace continuously at a velocity of 6 cm./min., and were subjected to primary firing in an air atmosphere and were then continuously carbonized in a nitrogen gas atmosphere, using the same furnace at a temperature from 300C. to 1200C.
The strengths and moduli of elasticity of the thus obtained various carbon fibers were measured. The results are shown in Table 3. It will be observed from Table 3 that, by converting a certain amount of carboxyl groups in acrylonitrile copolymer fibers to the salt form (-COOK), the physical properties of the obtained fibers are improved.
Table 3 Acrylonitrile copolymer fibers Carbon fibers .
pH of alkaline K conversionStrength Modulus of No. aqueous rate elasticity ~olution (mol %)(kg./mm2) (tons/mm2) 20 2 8 2.1 256 22 3 9 4.1 249 22 4 10 5.9 260 23 ~ 12 -. . . .
. - :
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing carbon fibers having excellent physical properties which comprises thermally stabilizing acry-lonitrile copolymer fibers in an oxidizing air atmosphere at a temperature of 150 to 400°C, and carbonizing the stabilized fibers in a non-oxidizing nitrogen atmosphere at a temperature of 800 to 2000°C, said fibers being made from an acrylonitrile copolymer produced by copolymerizing at least 80 mol %
acrylonitrile and 0.3 to 6 mol % of an unsaturated monomer cont-aining a carboxyl group and in which 0.1 to 15% of the terminal hydrogens of said carboxyl groups have been replaced with an alkali metal cation or ammonium ion.
acrylonitrile and 0.3 to 6 mol % of an unsaturated monomer cont-aining a carboxyl group and in which 0.1 to 15% of the terminal hydrogens of said carboxyl groups have been replaced with an alkali metal cation or ammonium ion.
2. A process according to Claim 1 wherein there are used acrylonitrile copolymer fibers which are made from an acrylo-nitrile copolymer produced by copolymerizing at least 80 mol %
acrylonitrile and 0.5 to 6 mol % of an unsaturated monomer containing a carboxyl group and in which 0.5 to 10% of the terminal hydrogens of said carboxyl groups has been replaced with an alkali metal cation or ammonium ion.
acrylonitrile and 0.5 to 6 mol % of an unsaturated monomer containing a carboxyl group and in which 0.5 to 10% of the terminal hydrogens of said carboxyl groups has been replaced with an alkali metal cation or ammonium ion.
3. A process according to claim 1 wherein said acrylonitrile copolymer contains at least 90 mol % acrylonitrile.
4. A process according to Claim 1 wherein said acrylonitrile copolymer fibers are obtained by treating acrylonitrile copolymer fibers in a water-swollen state obtained by wet-spinning an acrylonitrile copolymer produced by copolymerizing at least 80 mol % acrylonitrile and 0.3 to 6 mol % of an unsat-urated monomer containing a carboxyl group, with an aqueous solution containing an alkali metal cation or ammonium ion.
5. A process according to claim 1 wherein said acrylonitrile copolymer fibers are obtained by treating acrylonitrile copolymer fibers in a water-swollen state, obtained by wet-spinning an acrylonitrile copolymer, produced by copolymerizing at least 80 mol % acrylonitrile and 0.3 to 6 mol % of an unsaturated monomer containing a carboxyl group, using an aqueous solution of thiocyanate as a solvent, with an acid aqueous solution.
6. A process according to Claim 1 wherein said unsaturated monomer containing carboxyl group is selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, isocrotonic acid, itaconic acid, maleic acid, mesaconic acid, citraconic acid and their water-soluble salts.
7. A process as claimed in Claim 1 or Claim 5 wherein the carbonized fibers are subjected to a graphitizing step in a non-oxidizing atmosphere at a temperature of 2000 to 3500°C.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP49014209A JPS5133211B2 (en) | 1974-02-04 | 1974-02-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1040370A true CA1040370A (en) | 1978-10-17 |
Family
ID=11854702
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA219,386A Expired CA1040370A (en) | 1974-02-04 | 1975-02-04 | Process for producing carbon fibers having excellent physical properties |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4001382A (en) |
| JP (1) | JPS5133211B2 (en) |
| CA (1) | CA1040370A (en) |
| DE (1) | DE2504593B2 (en) |
| FR (1) | FR2259924B1 (en) |
| GB (1) | GB1481893A (en) |
Families Citing this family (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5231124A (en) * | 1975-09-01 | 1977-03-09 | Japan Exlan Co Ltd | Improved preparation of carbon fiber |
| JPS5920004B2 (en) * | 1977-03-23 | 1984-05-10 | 日本エクスラン工業株式会社 | Carbon fiber manufacturing method |
| JPS5848643B2 (en) * | 1977-04-05 | 1983-10-29 | 東レ株式会社 | High purity acrylic carbon fiber |
| IT1112296B (en) * | 1978-07-28 | 1986-01-13 | Snia Viscosa | HIGH FLAME RESISTANT ACRYLIC POLYMERS, YARNS CONSTITUTED FROM SUCH POLYMERS, AND MANUFACTURING PROCESS OF SUCH POLYMERS AND YARNS |
| US4336022A (en) * | 1979-08-01 | 1982-06-22 | E. I. Du Pont De Nemours And Company | Acrylic precursor fibers suitable for preparing carbon or graphite fibers |
| JPS5982421A (en) * | 1982-11-04 | 1984-05-12 | Mitsubishi Rayon Co Ltd | Production of carbon fiber |
| US4603041A (en) * | 1984-07-19 | 1986-07-29 | E. I. Du Pont De Nemours And Company | Cyclization of acrylic fiber |
| US5066433A (en) * | 1988-02-16 | 1991-11-19 | Hercules Incorporated | Method of manufacturing carbon fiber using preliminary stretch |
| CN101012296B (en) | 1998-10-27 | 2012-09-05 | 伊士曼化工公司 | Process for the polymerization of olefins, polyethylenes, and films and articles produced therefrom |
| US6171993B1 (en) | 1998-12-04 | 2001-01-09 | Equistar Chemicals, Lp | Enhanced-impact LLDPE with a shear modifiable network structure |
| US6323148B1 (en) | 1998-12-04 | 2001-11-27 | Equistar Chemicals, Lp | Ethylene polymerization catalyst and catalyst system |
| EP1397394B1 (en) * | 2001-05-07 | 2012-05-23 | Univation Technologies, LLC | Polyethylene resins |
| FR2842192B1 (en) * | 2002-07-12 | 2004-10-01 | Snecma Propulsion Solide | PROCESS AND PLANT FOR OBTAINING CARBON PRODUCTS FROM CARBON PRECURSOR PRODUCTS |
| EP2147776A1 (en) * | 2008-07-23 | 2010-01-27 | SGL Carbon SE | Method for manufacturing a compound material reinforced with fibre netting and compound material reinforced with fibre netting and its application |
| DE102009047491A1 (en) | 2009-12-04 | 2011-06-09 | Sgl Carbon Se | Production of a 3D textile structure and semifinished fiber products from fiber composites |
| DE102009047514A1 (en) | 2009-12-04 | 2011-07-07 | Sgl Carbon Se, 65203 | Fibers for the production of composite materials |
| 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 |
| US11299824B2 (en) | 2019-08-21 | 2022-04-12 | Hexcel Corporation | Selective control of oxidation atmospheres in carbon fiber production |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3027222A (en) * | 1957-09-03 | 1962-03-27 | Du Pont | Fireproof acrylonitrile copolymers |
| US3491179A (en) * | 1967-01-03 | 1970-01-20 | American Cyanamid Co | Preparation of acrylonitrile polymer fibers |
| US3635675A (en) * | 1968-05-28 | 1972-01-18 | Us Air Force | Preparation of graphite yarns |
| US3592595A (en) * | 1968-11-21 | 1971-07-13 | Celanese Corp | Stabilization and carbonization of acrylic fibrous material |
| GB1288563A (en) * | 1969-01-20 | 1972-09-13 | ||
| US3841079A (en) * | 1970-04-14 | 1974-10-15 | Celanese Corp | Carbon filaments capable of substantial crack diversion during fracture |
| US3817700A (en) * | 1970-09-14 | 1974-06-18 | Monsanto Co | Process for treating acrylic fibers to obtain carbonizable and graphitizable substrates |
| US3791840A (en) * | 1970-10-21 | 1974-02-12 | Union Carbide Corp | Treatment of carbon fibers to improve shear strength in composites |
| US3746560A (en) * | 1971-03-25 | 1973-07-17 | Great Lakes Carbon Corp | Oxidized carbon fibers |
| JPS4724185U (en) * | 1971-04-09 | 1972-11-17 | ||
| US3764662A (en) * | 1971-04-21 | 1973-10-09 | Gen Electric | Process for making carbon fiber |
| US3776829A (en) * | 1971-10-26 | 1973-12-04 | Great Lakes Carbon Corp | Aminated carbon fibers |
| US3954947A (en) * | 1972-11-17 | 1976-05-04 | Union Carbide Corporation | Rapid stabilization of polyacrylonitrile fibers prior to carbonization |
-
1974
- 1974-02-04 JP JP49014209A patent/JPS5133211B2/ja not_active Expired
-
1975
- 1975-01-20 US US05/543,008 patent/US4001382A/en not_active Expired - Lifetime
- 1975-01-27 GB GB3521/75A patent/GB1481893A/en not_active Expired
- 1975-02-03 FR FR7503308A patent/FR2259924B1/fr not_active Expired
- 1975-02-04 CA CA219,386A patent/CA1040370A/en not_active Expired
- 1975-02-04 DE DE19752504593 patent/DE2504593B2/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2504593A1 (en) | 1975-08-07 |
| JPS50107219A (en) | 1975-08-23 |
| JPS5133211B2 (en) | 1976-09-18 |
| FR2259924B1 (en) | 1977-11-25 |
| DE2504593B2 (en) | 1976-09-23 |
| US4001382A (en) | 1977-01-04 |
| FR2259924A1 (en) | 1975-08-29 |
| GB1481893A (en) | 1977-08-03 |
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