US3723609A

US3723609A - Process for the production of carbon fibers

Info

Publication number: US3723609A
Application number: US00078943A
Authority: US
Inventors: M Mansmann; G Winter; G Pampus; N Schon
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1969-10-17
Filing date: 1970-10-07
Publication date: 1973-03-27
Anticipated expiration: 1990-03-27
Also published as: GB1323765A; CH540852A; DE1952388A1; AT310343B; DE1952388B2; BE757620A; ES384640A1; NL7015164A; CA938416A; FR2066130A5

Abstract

In the production of carbon fibers wherein a carbon-containing fiber-forming material is spun as a solution, the spun-filaments are converted to solid fibrous material, and the fibrous material is carbonized, the improvement which comprises including in said solution at least one fiber-forming high polymer at a concentration of about 0.001 to 10 percent by weight and a greater amount of a carbon source comprising at least one carboncontaining organic material having a softening or melting point in excess of about 80* C., whereby the solution of said carbon containing material is rendered spinnable by addition of said fiber-forming high polymer, said carbon containing organic material serving as the source of carbon for the carbon fiber; the fiber may thereafter be graphitized. The spinning solution used for fiber production is preferably a solution in a volatile solvent so that it may be dry spun. The carbon source in said solvent by itself would not be spinnable and may be a monomer or low polymer.

Description

United States Patent Mansmann et al.

PROCESS FOR THE PRODUCTION OF CARBON FIBERS Inventors: Manfred Mansmann; Gerhard Winter, Krefeld; Gottfried Pampus; Hildegard Schnoring, both of Leverkusen; Nikolaus Schon, Wuppertal- Elbergeld, all of Germany Assignee: Bayer Aktiengesellschaft, Leverkusen, Germany Filed: Oct. 7, 1970 Appl. No.: 78,943

Foreign Application Priority Data 0a. 17, 19:69 Ger many ..P 19 52 388.7

US. Cl. ..423/447, 264/29, 264/ 176 F Int. Cl. ..C0lb 31/07 Field of Search ..'....23/209.1, 209.2, 209.4; 264/29, 204, 205, 207, 176; 260/6, 8, 9 R,

17, 17.4 R, 17.4 ST, 17.4 SG

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS 3,820,609 10/1963 Japan ..23/209.l

Primary Examiner-Edward J. Meros Attomey-Burgess, Dinklage & Sprung ABSTRACT In the production of carbon fibers wherein a carboncontaining fiber-forming material is spun as a solution, the spun-filaments are converted to solid fibrous material, and the fibrous material is carbonized, the improvement which comprises including in said solution at least one fiber-forming high polymer at a con centration of about 0.001 to 10 percent by weight and a greater amount of a carbon source comprising at least one carbon-containing organic material having a softening or melting point in excess of about 80 C., whereby the solution of said carbon containing material is rendered spinnable by addition of said fiber-forming high polymer, said carbon containing organic material serving as the source of carbon for the carbon fiber; the fiber may thereafter be graphitized. The spinning solution used for fiber production is preferably a solution in a volatile solvent so that it may be dry spun. The carbon source in said solvent by itself would not be spinnable and may be a monomer or low polymer.

16 Claims, No Drawings Carpenter et al ..23/209.l 1 I PROCESS FOR THE PRODUCTION OF CARBON FIBERS This invention relates to the production of carbon fibers predominantly from materials which are not normally spinnable as a solution.

Numerous proposals are found in the literature for' the production of carbon fibers. Carbon fibers are generally produced through carbonizing an organic starting material in the form of fibers by a thermal treatment in an inert gas. The carbon fibers thus produced are converted into graphite fibers by further heating to temperatures of up to about 3 ,000 C.

To produce strong and flexible carbon fibers, the starting fibers must not only be readily producible but also fulfil the following important requirements:

a. The material must not pass through a tacky or liquid state in the course of carbonization which would cause the fibers to stick together and lose their flexibility.

b. The carbon residue should be as high as possible. c. In order to obtain high volume/time yields in the production process, the original fiber must be able to withstand a rapid temperature increase without loss in strength and flexibility of the resulting carbon fibers. The starting material must be readily available in a fibrous form. The starting material should be inexpensive.

Numerous starting materials have been proposed but none of them fulfil all these conditions. Carbon and graphite fibers have been obtained, for example, by the carbonization and, where indicated, the graphitization of natural or regenerated cellulose, polyacrylonitrile, polyvinyl alcohol, polyvinyl chloride and specially pretreated woolen fibers (0. Vohler, E. Sperk: Ber. Dtsch. Keram. Ges. 43 [1966] pages 199208).

According to French Patent Specification No. 1,465,030, molten bitumen or tar pitch is spun into fibers at temperatures of at least 240 C., and these fibers are then used as starting fibers for the production of carbon and graphite fibers. The object of this process is this process is to enable inexpensive fiber materials to be used as starting materials for carbon fibers, which are not normally available in fibrous form. Apart from the fact that the material has tobe spun at a high temperature, one of the major disadvantages of the process is that the starting material must first be adjusted to a quite specific C/H ratio in a separate process step, and the tar fibers must be rendered infusible before the carbonization by pretreating them with ozone or peroxides, followed by oxidation in air.

Of all the many carbon compounds, therefore, only a very few substances can be used as starting materials for carbon fibers. One of the reasons why some of the substances which appeared to be suitable could not be used was that they are not available in a fibrous form. If a substance is to be spun from the fluid phase into fibers by the conventional methods of the man-made fiber industry, it is essential for the spinning process that the fluid phase should be spinnable. The spinna bility of a fluid substance is manifested by the fact that when a glass rod is dipped into such a solution and removed from it, the liquid is drawn up with the rod as a thread of substantial length and does not, as is normally the case, drip from the rod. Spinnability is a quite specific state. The number of spinnable substances is accordingly limited and substantially comprises the known materials ofthe man-made fiber industry.

In this context, the term carbonization is understood to mean the heat treatment of an organic substance to temperatures below 2,000" C., preferably to about 1,000 C., heating being carried out at a temperature of at least about 400 C. in an inert gas at normal or reduced pressure. Graphitization is understood to mean a heat treatment at temperatures of between 2,000 C. and about 3,000 C. under a protective gas atmosphere.

It is accordingly an object of the invention to solve the problem by providing a simple method of producing spinnable solutions of numerous substances which are not spinnable as such but which otherwise fulfil the conditions for the production of carbon fibers.

The process according to the invention for the production of carbon and graphite fibers by carbonization, and if indicated graphitization, of starting fibers which contain carbon is characterized in that the starting fibers which contain carbon are produced by spinning solutions, which, in addition to at least one organic substance which has a melting or softening point above approximately C. and which can be decomposed to carbon by a carbonization treatment, also contain 0.001 to 10 percent by weight of at least one fiber-forming high polymer substance which has a chain structure and which is soluble in the solvent.

In accordance with this invention, determination of the spinnability is carried out by a process which has been described in the literature and which is similar to the usual process employed in the case of dry spinning. The liquid under investigation is extruded from a nozzle under pressure and the length in centimeters of the uninterrupted filament of liquid, measured up to the point where it breaks up into individual droplets, is taken as a measure of the spinnability (Kolloid- Zeitschrift 61 [1932] page 258). In the measurements carried out, the solutions were extruded at room temperature under a pressure of 0.5 atmosphere gauge from a nozzle which had a nozzle diameter of 400 microns and a length of nozzle duct of 17 mm.

It was surprisingly found that a solution of an organic substance which is suitable as a starting material for the production of carbon fibers, i.e. which can be decomposed into carbon by a carbonization treatment but which is not spinnable as such (hereinafter termed the carbon source or source of carbon) can be rendered spinnable in a simple manner by the presence of small quantities of high molecular weight linear polymers (hereinafter referred to as fiber-forming substances) or fiber-forming high polymers. The fiber-forming substances are added in quantities of about 0.001 to 10 percent by weight, preferably about 0.01 to 5 percent by weight. For allpractical purposes, these concentrations are sufficient for achieving spinnability. Furthermore, it is one of the characteristics of the'invention that spinning can be carried out with inexpensive carbon sources, which are by-products or waste products ofother processes, with addition of high polymer fiberforming substances in only very small'amountwith obviouseconomic advantage.

The concentration of the carbon source in the'solution can vary within wide limits. Solutions having concentrations of from about 5 to 60 percent can be used but the concentration of the carbon source in the solutions used for spinning is generally between about and 40 percent by weight.

The process enables carbon and graphite fibers to be obtained for the first time from numerous organic starting materials which could not hitherto be used since they could not be obtained in the form of fibers. Thus it is now possible to process inexpensive by-products or waste products of natural or synthetic origin into fibers from which carbon and graphite fibers can then be obtained. The necessary condition for the suitability of an organic material is a sufficiently high carbon residue in the carbonization process which of course depends upon the initial carbon content and should preferably be at least about 10 percent by weight of the starting material. In addition, the material must not pass through a liquid or tacky state in the course of carbonization. This is ensured whenever the melting point is substantially above the decomposition temperature.

The following are mentioned as examples of the large number of suitable starting materials which are available in practice: Carbohydrate derivatives such as starch, partly degraded or oxidized starch, dextrin, hemicellulose, cellulose derivatives such as methyl cellulose, vegetable gums, polymeric sugar derivatives such as polyuronic acids, e.g. pectin, pectinic acid or alginic acid, proteins such as casein, gelatine or fish glue, organic acid derivatives which are capable of internal salt formation such as glycocol or betaine, sulfonic acids, their substitution products and their salts, especially ammonium slats, lignin, ligninsulfonic acid and its salts, in particular ammonium lignin sulfonate.

According to the process. of the invention, substances whose melting or softening point is below the decomposition temperature may also be used as carbon sources provided the fibers spun from them are treated so that they will maintain their fibrous character during the actual carbonization, e.g. as by being rendered in-. fusible. In this case, the melting or softening point of the substances used as carbon sources should not be substantially below about 80 C. Numerous measures are already known in the literature by which fiber materials which soften before their decomposition can be rendered infusible.

A process for producing carbon or graphite fibrous material from a starting material which contains wool has been claimed in German Auslegeschrift 1,255,629. Since the starting material which contains wool would lose its fibrous structure by a heat treatment, this must be prevented by special measures which comprise heating the starting material to about 200 C. with access of air at such a rate that the temperature rises by from 5 to 50 C. per hour. Heating is then continued to a temperature of about 300 C. under a restricted air supply and at a rate of temperature increase of 1 to 10 C. per hour, and the temperature is then raised to about l,000 C. with exclusion of air at a rate of temperature increase of 10 to 100 C. per hour, and'heating is carried out at least partly in an atmosphere which contains formaldehyde, ammonia and/or carbon dioxide.

According to French Patent Specification No. 1,465,030 which has already been cited, tar fibers can be rendered infusible by a treatment with ozone or peroxides followed by oxidation in air. In Belgian Patent Specification No. 718,561, fibers of vinyl chloride copolymers, polyvinyl alcohol derivatives and/or polyvinyl alcohol are rendered infusible by a treatment with acid condensing agents below the softening temperature of the fibers. The condensing agents used are preferably concentrated sulfuric acid or difluoroand hexa-fluorophosphoric acid. Polyvinyl alcohol, which melts at about 230 C. in inert gas, can be rendered infusible simply by a preliminary oxidation with air. A. Shindo et al. (Polymer Preprints, 9, No. 2 [1968] page 1,327) moreover found that preoxidized polyvinyl alcohol yields a much higher carbon residue when pyrolysis is carried out in the presence of gaseous HCl than when it is carried out under inert gas.

The following are mentioned as examples ofthe large number of starting materials which soften or melt when heated and therefore have to be rendered infusible prior to carbonization: Polyvinyl alcohol, polyvinyl acylates, polyvinyl chloride, polyolefins, polyesters, polyethers, polyanhydrides, polyurethanes, polyamides, polyureas, phenol formaldehyde resins, both as pure polymers and in the form of their copolymers, graft polymers and derivatives and the like. In contrast to the fiber-forming substances, these polymers which are used as carbon sources need not have a linear polymeric structure and they also differ from fiberforming substances by having a lower degree of polymerization. Addition of a fiber-forming substance also confers spinnability on solutions of these polymers.

Carbon sources in accordance with this invention are therefore any low molecular weight or higher molecular weight organic substances which have melting or softening points above approximately C., are soluble in a solvent and can be decomposed to carbon by a carbonization treatment. Carbon sources include especially those substances which in addition to having the above mentioned features have a spinnability of less than 10 cm as 10 percent solutions. The carbon residue from carbonization should be at least about 10 percent by weight of the carbon source.

It must be emphasized that the process according to the invention makes it possible for the first time to convert molecular disperse solutions and those of low polymers, in particular those which have a degree of polymerization below about 50, into fibers by a dry spinning process (as defined in Ullmanns'Encyklopadie der technischen Chemie 7 [1956] page 263) and hence make them available as starting materials for carbon fibers. Compounds of this type frequently have the advantage over macromolecular substances of being more soluble so that they can be used in higher concentrations in solutions.

The fiber-forming substances which are used according to the invention are characterized not only by their linear polymer structure but also by'their degree of polymerization or molecular weight. It is only above a certain degree of polymerization that solutions of high polymers manifest the property of spinnability at concentrations below 5 percent. The choice of the fiberforming substance depends on the particular solvent used. For aqueous solutions, water-soluble high polymers are used, preferably polyethylene oxide, polyacrylamide or acrylic acid/acrylamide copolymers and the like. In organic media, one may use not only the substances mentioned above but also other high polymer substances such as polystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene, and the like.

Solutions of linear polymeric substances have been in use for a long time in spinning processes of the manmade fiber industry. These solutions also have the property of spinnability but the molecular weights and degrees of polymerization of the substances used for these purposes are substantially lower than in the substances used according to the invention. These solutions are not sufficiently spinnable until they have concentrations in the region of 25 to 45 percent. Thus, for example for the production of polyacrylonitrile fibers a 25 percent solution of a polyacrylonitrile having a molecular weight of 35,000 to 50,000, which cor responds to a degree of polymerization of 660 to 950, is spun in dimethyl formamide (Ullmanns Encyklopadie der technischen Chemie, 7 [1956]). If such substances are made up into 0.01 to 5 percent solutions in a suitable solvent, they are not spinnable. When extruded through a nozzle, they only form a series of droplets but no coherent fibers.

The spinnability of high polymer solutions at the low concentrations used in the process of the present invention depends decisively on the degree of polymerization of the substance used. To illustrate this fact, the conditions in aqueous and organic media will now be explained with the aid of a few examples.

2 percent aqueous solutions of polyethylene oxide may achieve various values of spinnability depending on the molecular weight or degree of polymerization. The solution of a polyethylene oxide A having a degree of polymerization DP of 5,450 has a spinnability of only 30 cm, the solution of a polyethylene oxide B (DP 17,000) has a spinnability of 130 cm, polyethylene oxide C (DP 68,200) a spinnability of 225 cm, and the spinnability of a polyethylene oxide D with DP 136,400 is already far above 300 cm. To specify the substances more accurately, the limiting viscosity number [1;] determined in water at 35 C. at a shear stress of1-= 12.5 dyn/cm is also indicated (Table 1).

The limiting viscosity number also known as the intrinsic viscosity is defined as follows:

1;,= relat. viscosity 1 /1 071 viscosity of the solution; 1 viscosity of the solvent; c concentration in g/l 00 ml.

At a degree of polymerization of 136,400 [1;] 9.15), a 1.5 percent aquous polyethylene oxide solution already has a spinnability of 300 cm. If a solution of a carbon source which is not spinnable as such contains 1.5 percent of this polyethylene oxide, this solution will have a spinnability of several meters. The spinnability of the high molecular weight polyethylene oxide has been transmitted to the particular solution. If

similarly high values of spinnability are to be achieved with a polyethylene oxide of low degree of polymerization, the concentration of this polyethylene oxide must be correspondingly higher. Thus, for example a spinnability of 300 cm will also be achieved with a polyethylene oxide having a degree of polymerization.

of 6,800 if the aqueous solution contains 2.5 percent.

For aqueous systems, polyacrylamides or acrylamide/acrylic acid copolymers and salts thereof are also suitable. Thus, for example, a copolymer of acrylamide and acrylic acid which consists to an extent of percent of polyacrylamide and which has a degree of polymerization of 14,080 has a spinnability of 300 cm when present as a 1.7 percent aqueous solution. A higher molecular weight product with a degree of polymerization of 70,400 has a spinnability of 300 cm when its concentration in water is only 0.25 percent. The inherent viscosity (In 1 r)/c (determined in water, 25 C., pH 7; 0,05 percent solution with 0.1 percent NaCl at 'r 0.98 dyn/cm where c is the concentration in gram per ml. of the solvent) of this product is 35. The proportion of acrylamide to acrylic acid in' the copolymers may have any value between 0 l and 1 0. A copolymer containing 2.5 percent of acrylamide (97.5 percent of acrylic acid) has a spinnability of 210 cm when present as a 0.8 percent solution. Similarly high spinnability is also achieved if the acrylic acid of TABLE 2 Substance Degree of Concentration Spinnability polymerization Percent by (cm) wt. in CH,C1,

Polystyrene A 1,038 3 l Polystyrene 8 20,200 3 10 Polystyrene C 25,000 3 20 Polystyrene D 27,900 3 50 Polystyrene E 34,600 3 1 l0 Polystyrene F 125,000 0,15 300 Similar conditions are also found in the case of other high polymers, e.g. solutions of polyisobutylene in trichloroethylene (Table 3).

TABLE 3 Substance Degree of Concentration Spinnability polymerization (Percent by (cm) weight in trichloroethylene) Polyisobutylene A 6,900 3 4 B 23,600 3 20 C 49,000 3 60 D 85,500 1.5 300 The 3 percent solution in CH Cl of a polymethyl methacrylate with a degree of polymerization of 3,600 is found to have a spinnability of cm whereas at a degree of polymerization of 15,000 a 2 percent solution in CH Cl has a spinnability of 300 cm. 3 percent solutions of polyisoprene, e.g. in toluene or trichloroethylene, are also spinnable (degree of polymerization DP 25,000).

Polyethylene oxide which can be spun in the form of an aqueous solution also manifests this property in organic solvents such as CH Cl An increase in spinnability with the degree of polymerization is again observed here. The effect is even greater in CH Cl than in water. Polyethylene oxide with a degree of polymerization of 6,800 has a spinnability of 300 cm already at a concentration of only 0.2 percent.

These phenomena can also be produced with other high polymers which have a chain structure, including e.g. vinyl polymers an copolymers, diolefin polymers, polydienes, substituted polyethers and thioethers,

polyesters, polyamides, polypeptides, polysaccharides,

polysiloxanes, and mixtures of these substances, and the like. The limits for the occurrence of spinnability may shift slightly according to the nature of the high polymer substance and of the solvent used. In all cases, however, one observes that substances of high limiting viscosities numbers [1 or high degrees of polymerization are spinnable in solutions of very low concentration, and this spinnability can be transferred to solutions of carbon sources. When using polymer substances which have a low degree of polymerization as found in most commercially available products, however, it is found that dilute solutions are not spinnable, just as polyethylene oxide could not be spun at degrees of polymerization of below 2,000.

Fiber-forming substances within the meaning of the present invention are therefore high polymer organic soluble compounds which have a linear polymeric structure. They preferably have degrees of polymerization above approximately 2,000.

The usual commercial solvents may be used. Their choice will depend on the solubility of the carbon source. It is advantageous to use solvents with boiling points below about 200 C. The solvent used is preferably water.

To produce the spinning solutions, a solution of the fiber-forming substance is added to the solutions of the carbon source until the solution iscapable of producing fibers, i.e. until sufficient spinnability is obtained, which generally occurs in the region of from 0.01 to 2 percent by weight of the fiber-forming substance based on the total amount of the solution. If desired, the carbon source may also be dissolved directly inthe solution of the fiber-forming substance. The concentration of the carbon source may vary within wide limits. At high concentrations, a lower concentration of the fiberforming substance is generally sufficient whereas at lower concentrations of the carbon source it is necessary to use larger quantities of the fiber-forming substance. The quantity also depends on the nature of the solution, more highly viscous solutions generally requiring less fiber-forming substance than thin, very liquid solutions. The spinnability of the solution should be at least above 50, advantageously at least above 100 and preferably at least above 200.

In some cases, it has been found advantageous to adjust the spinning solution to a certain pH value, either because the solubility of the carbon source is thereby increased or because the viscosity. of the spinning solution depends upon the pH. In some cases, solidification of the fiber in the spinning column can be accelerated by a change in pH. Thus, for example an ammoniacal solution of ammonium lignin sulfonate which contains polyethylene oxide is highly fluid whereas the same solution at or near a neutral pH is much more viscous. When spinning the ammoniacal solution, the pH in the fiber falls due to the evaporation of NH and the viscosity therefore rises. This, together with the increase in concentration due to evaporation of solvent, leads to solidification of the fiber. To adjust to a pH below 7, the known inorganic acids, especially hydrohalic acids,-may be added. it is preferable, however, to use organic monoor polycarboxylic acids such as formic acid, acetic acid or oxalic acid, advantageously in quantities of from about 1 to 60 percent.

The spinning solutions thus obtained have numerous advantageous properties. Apart from having good spin-v nability, the relatively low viscosity and the ease with which they can therefore be handled are added advantages. The viscosity of these solutions may lie between about 0.1 to 100 poise but preferably from about 1 to 10 poise, therefore below the values usually required for spinning processes. The spinning solutions are therefore easily to be filtered, easily to be degasified, and'can easily be pumped through pipes.

Spinning may be carried out by either the wet or the dry spinning process but a conventional dry spinning process is preferably employed. The solutions are spun from a multiaperture spinning die substantially at temperatures below the boiling point of the solvent used. The filaments pass through a spinning column which can be heated to several hundred degrees centigrade, depending on the solvent used, and which may be traversed by a current of air or inert gas in the usual manner. In the column, the fibers are drawn out to a diameter of from about 50 to about 1 micron. At the same time, most of the solvent is removed. The filament, which is at first highly fluid, is concentrated in the process and is converted into the gel state via a highly viscous state. At the stage of gel formation, the filaments may still contain some solvent. After leaving the spinning column, the filaments are collected. These filaments are the actual starting material for the production of carbon and graphite fibers.

The fibrous starting material is now converted in the conventional manner either continuously or intermittently into fibers consisting substantially of more than 97 percent of carbon by increasing the temperature to about l,000 C. 2,000 C.; heating must be carried out in a stream of an inert gas at a temperature of at least about 400 C. In some cases, the starting fibers are pretreated before the actual carbonization process. This pretreatment may consist of a special gas treatment, for example with HCl, C1 N0 or 0 either to improve the behavior during carbonization or to render the fibers infusible.

In any particular case, the temperature treatment depends on the starting material used for providing the carbon. The measures described in the patent literature for the known processes for the production of carbon fibers may be used as a guide for successful carbonization.

Carbon fibers may also be graphitized by a thermal treatment at a temperature from about 2,000 C. to about 3,000 C. under a protective gas.

The carbon and graphite fibers produced according to the invention may be used for numerous purposes. Yarns, woven fabrics, felts and wadding can be produced by conventional processes, and these products may be used, for example, for high temperature insulation, as filters for hot, corrosive gases and liquids, as reinforcing components in composite materials and as catalysts and catalyst carriers.

The following Examples serve to illustrate the range of application of the process according to the invention. All concentrations are given in percent by weight, e.g. 10 percent; which means that 10 grams of solid are dissolved in 90 grams of liquid.

Example 1 300 g of an aqueous 40 percent ammonium lignin sulfonate solution (SAP/N of Zellstoff Waldhof) were mixed with 100 g of a 2 percent aqueous polyethylene oxide solution (WSR 301 of UCC with [1;] 9.15) and 45 g of water. The solution was homogenized with the introduction of ammonia gas up to a pH of 10. The filtered spinning solution which contained 27 percent of ammonium lignin sulfonate and 0.45 percent of polyethylene oxide was spun in a column which was heated to 80 C. and washed with dry air. The spun filaments were taken up on a rotating drum. The spinning cake removed from the drum was heated from 100 to 250 C. in air in the course of 1 hour. The fibers were then heated in a stream of nitrogen, first to 400 C. at a rate of temperature increase of 40 per hour and finally to 1,000 C. at a rate of temperature increase of 150 per hour. Flexible carbon fibers were obtained (carbon yield: 36 percent). A part of the carbon fibers was subjected to a graphitization treatment by heating for 2 hours to 2,600 C. under an argon atmosphere.

Similarly prepared 40 percent and 27 percent ammonium lignin sulfonate solutions are not spinnable to any measurable extent without the addition of polyethylene oxide.

Example 2 300 g of dextrin, 300 g of glacial acetic acid and 300 g of water were boiled until completely dissolved. 430 g of the filtered solution were concentrated by evaporation to 320 g and mixed with 214 g of a 2 percent aqueous solution of a copolymer of acrylic acid and acrylamide (Praestol 2935 of Stockhausen having an inherent viscosity of (In 1 r)/c 35.0) to form a spinning solution which contained 24 percent dextrin and 0.8 percent of acrylic acid/acrylamide copolymer. This solution was spun as described in Example 1. The dextrin filaments were kept under nitrogen at 220 C. for hours. The fibers were then heated in a stream of nitrogen to 400 C. at a rate of temperature increase of 10 C. per hour and then to 1,000 C. at a rate of temperature increase of 150 per hour. Flexible carbon fibers were obtained (carbon yield: 18 percent). A 24 percent dextrin solution prepared in a similar manner without the thread forming substance has a spinnability of only 3 cm.

Without the addition of polyethylene oxide, the fish I glue solution was entirely unspinnable. Example 4 300 g of gelatine were dissolved in 300 g of hot water and mixed with 300 g of glacial acetic acid and 600 g of a 2 percent aqueous solution of an acrylic acid/acrylamide copolymer (Praestol 2935 of Stockhausen, viscosity (ln '1 .r)/c 35.0). The solution, which contained 0.8 percent of an acrylic acid/acrylamide copolymer in addition to 20 percent of gelatine, was spun into gelatine filaments as in Example 1. The gelatine fibers were converted into carbon fibers (carbon yield: 21 percent) by carbonization in a stream of nitrogen (5 hours kept at 220 C., heated up to 400 C. at'a rate of temperature increase of 30 per hour, and up to 1,000 C. at a rate of increase of 150 per hour). A 10 percent gelatine solution prepared in a similar manner without the fiber-forming substance is not spinnable. Example 5 v A spinning solution containing 8.8 percent of alginic acid and 0.5 percent of acrylic acid/acrylamide copolymer was obtained by dissolving g of alginic acid in 560 g of formamide and then thoroughly homogenizing this solution with 680 g of a 1 percent solution in formamide of the acrylic acid/acrylamide copolymer used in Examples 2 and 4, and the resulting product was spun as in the previous examples to produce alginic acid filaments. Carbon fibers could be obtained from these filaments by carbonization in a manner analogous to Example 2. Without the fiberforming substance, an 8.8 percent alginic acid solution in formamide was not spinnable. Example 6 33 g of starch (amylium solubile of Merck), 33 g of water and 33 g of glacial acetic acid were concentrated by boiling to 62 g. After the addition of 15.5 g of water,

82.5 g of 2 percent aqueous acid/acrylamide copolymer solution (see Examples 2 and 4) and 5 g of 27 g of casein were dissolved in dilute aqueous ammonia and adjusted to a concentration of 20 percent. A spinning solution containing 12.5 percent of casein and 0.75 percent of polyethylene oxide was obtained by the addition of 37.5 g of 2 percent aqueous polyethylene oxide, using the same polyethylene oxide as in Examples l and 3. This spinning solution was spun in a manner analogous to Example 1 to produce casein filaments. Carbon fibers (carbon yield: 22 percent) were obtained from these filaments by carbonization as described in Example 2. A solution prepared in a similar manner with 12.5 percent of casein but without the addition of polyethylene oxide is entirely unspinnable. Example 8 Polyvinyl acetate having a degree of polymerization of about 430 was made up into a 30 percent solution in methylene chloride. This solution was not spinnable. By the addition of 20 g of 3 percent solution of polymethylmethacrylate (degree of polymerization DP 15,000) in methylenechloride to l g of the polyvinyl acetate solution, a spinning solution was obtained which contained 25 percent of polyvinyl acetate and 0.5 percent of polymethylmethacrylate. This spinning solution was spun as in Example 1 to produce polyvinyl acetate filaments. Since polyvinyl acetate melts above approximately 100 C., the spun filaments first had to be rendered infusible. For this purpose, a part of the fibers was treated for 2 hours at room temperature with a stream of nitrogen of l/h which before its entry into the reaction chamber had been charged with SO by passing it through 60 percent oleum. The fibers which were colored black by the S0 treatment, were heated to 1,000 C. in a stream of nitrogen within 3 hours. The carbon yield was 19 percent. This is very different from the case of polyvinyl acetate which had been heated to 1,000 C. under nitrogen without previous SO treatment and in which the carbon yield was only 5.3 percent. Example 9 35 g of naphthol-l-disulfonic acid-(3,8) were dissolved in 65 g of a 9 percent ammonia solution. The solution was not spinnable. A spinning solution containing 24.8 percent of naphthol-l-disulfonic acid- (3,8) and 0,57 percent of polyethylene oxide was obtained by the addition of 41 g of a 2 percent aqueous polyethylene oxide solution, using the same polyethylene oxide as in Examples 1, 3 and 7. This spinning solution was spun into filaments in a manner analogous to Example 1. Carbonization under nitrogen (rate of heating to 400 C.: 57 C./h and between 400 C. and 1,000 C.: 170 C./h) yielded flexible carbon fibers (carbon yield: 40 percent) What is claimed is:

1. In the production of carbon fibers wherein a carbon-containing fiber-forming material is extruded in solution, the solution is converted to solid fibrous,

material, and the fibrous material is carbonized, the improvement which comprises forming said solution by dissolving in a solvent to a concentration of about 0.001 to 10 percent by weight at least one fiber-forming linear high polymer having a degree of polymerization in excess of about 2,000, and a greater amount of a carbon source comprising at least one carbonizable carbon-containing organic material having a softening or melting point in excess of about 80 C.'and a degree of polymerization below about 2,000, whereby said fibenforming linear high polymer imparts to said solution a spinnability of at least 50 cm.

2. Process according to claim 1, wherein the solution has a spinnability of at least 100 cm.

3. Process according to claim 1, wherein the solution has a spinnability of at least 200 cm.

4. Process according to claim 1, wherein the carbonized fiber is thereafter graphitized.

5. Process according to claim 1, wherein, said carbon source is a material leaving a carbon residue after carbonization which is at least about 10 percent by weight of the original material and, when dissolved alone in said solvent to a concentration of 10 percent, has a spinnability of less than about 10 cm.

6. Process according to claim 5, wherein said solvent is volatile and said solution is converted to fibrous material by dry spinning.

7. Process according to claim 1, wherein said solution comprises an aqueous solution of said fiber-forming material and said carbon source.

8. Process according to claim 7, wherein said carbon source is at least one of lignin, derivatives of lignin, carbohydrate derivatives and proteins.

9. Process according to claim 8, wherein the derivatives of lignin are lignin sulfonic acid and alkali metal, alkaline earth metal, and ammonium salts of lignin sulfonic acid.

10. Process according to claim 1, wherein said carbon source comprises a monomer or a polymer having a degree of polymerization less than about 50.

11. Process according to claim 1, wherein said carbon source is selected from vinyl polymers, polyethers, polyesters, polyanhydrides, polyurethanes, polyureas, polyamides, phenol formaldehyde resins, polyolefins, and mixtures, derivatives or copolymers thereof.

12. Process according to claim 1 1, wherein after conversion of the solution into fibrous material, the fibrous material is treated to render said carbon source infusible during subsequent carbonization.

13. Process according to claim 1, wherein said solution contains said fiber-forming high polymer in a concentration of about 0.01 to 5 percent by weight.

14. Process according to claim 13, wherein said fiber-forming high polymer is at least one of polystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers, diolefin polymers, polydienes, polyethylene oxide, substituted polyethers and thioethers, polyesters, polyamides, polypeptides, polysaccharides, polysiloxanes, and polyacrylamide or acrylic acid/acrylamide copolymers or their alkali metal or ammonium salts.

15. Process according to claim 8, wherein said fiberforming high polymer is selected from polyethylene oxide, polyacrylamide, and acrylic acid/acrylamide copolymers or their alkali metal ammonium salts or substituted ammonium salts having an inherent viscosity (In 1; r)/c above 4 (determined at a shearing stress r 0.98 dynlcm' 25 C., pH 7, 0.05 percent solution with 0.1 percent NaCl).

16. Process according to claim 12, wherein said fiber-forming high polymer is at least one of polystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers, diolefin polymers, polydienes, polyethylene oxide, substituted polyethers and thioethers, polyesters, polyamides, polypeptides, polysaccharides, polysiloxanes, polyacrylamide, and acrylic acid/acrylamide copolymers or their alkali metal, ammonium, and substituted ammonium salts present in the solution in a

Claims

2. Process according to claim 1, wherein the solution has a spinnability of at least 100 cm.
3. Process according to claim 1, wherein the solution has a spinnability of at least 200 cm.
4. Process according to claim 1, wherein the carbonized fiber is thereafter graphitized.
5. Process according to claim 1, wherein, said carbon source is a material leaving a carbon residue after carbonization which is at least about 10 percent by weight of the original material and, when dissolved alone in said solvent to a concentration of 10 percent, has a spinnability of less than about 10 cm.
6. Process according to claim 5, wherein said solvent is volatile and said solution is converted to fibrous material by dry spinning.
7. Process according to claim 1, wherein said solution comprises an aqueous solution of said fiber-forming material and said carbon source.
8. Process according to claim 7, wherein said carbon source is at least one of lignin, derivatives of lignin, carbohydrate derivatives and proteins.
9. Process according to claim 8, wherein the derivatives of lignin are lignin sulfonic acid and alkali metal, alkaline earth metal, and ammonium salts of lignin sulfonic acid.
10. Process according to claim 1, wherein said carbon source comprises a monomer or a polymer having a degree of polymerization less than about 50.
11. Process according to claim 1, wherein said carbon source is selected from vinyl polymers, polyethers, polyesters, polyanhydrides, polyurethanes, polyureas, polyamides, phenol formaldehyde resins, polyolefins, and mixtures, derivatives or copolymers thereof.
12. Process according to claim 11, wherein after conversion of the solution into fibrous material, the fibrous material is treated to render said carbon source infusible during subsequent carbonization.
13. Process according to claim 1, wherein said solution contains said fiber-forming high polymer in a concentration of about 0.01 to 5 percent by weight.
14. Process according to claim 13, wherein said fiber-forming high polymer is at least one of polystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers, diolefin polymers, polydienes, polyethylene oxide, substituted polyethers and thioethers, polyesters, polyamides, polypeptides, polysaccharides, polysiloxanes, and polyacrylamide or acrylic acid/acrylamide copolymers or their alkali metal or ammonium salts.
15. Process according to claim 8, wherein said fiber-forming high polymer is selected from polyethylene oxide, polyacrylamide, and acrylic acid/acrylamide copolymers or their alkali metal ammonium salts or substituted ammonium salts having an inherent viscosity (ln eta r)/c above 4 (determined at a shearing stress Tau 0.98 dyn/cm2, 25* C., pH 7, 0.05 percent solution with 0.1 percent NaCl).
16. Process according to claim 12, wherein said fiber-forming high polymer is at least one of polystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers, diolefin polymers, polydienes, polyethylene oxide, substituted polyethers and thioethers, polyesters, polyamides, polypeptides, polysaccharides, polysiloxanes, polyacrylamide, and acrylic acid/acrylamide copolymers or their alkali metal, ammonium, and substituted ammonium salts present in the solution in a concentration of about 0.01 to 5 percent and the solution is formed into fibrous material by dry spinning.