Wet Spinning Method For Producing A Lignin-containing Fiber As A Precursor For A Carbon Fiber

Abstract

The invention relates to a method for producing a precursor fiber which is suitable for further processing into carbon and activated carbon fibers. The method is a wet spinning method in which a spinning solution consisting of lignin or lignin derivatives, cellulose carbamate, and alkali lye are pressed through the holes of a nozzle and introduced directly into a coagulation bath. The precursor fibers falling into the bath can undergo different additional method steps: they can be stretched, post-treated, dried at an increased temperature, and wound. Because the precursor fibers constitute an inexpensive starting material, the precursor fibers can be used in connection with the production of carbon and activated carbon fibers.

Description

[0001] The invention relates to a method for producing a precursor fiber which is suitable for further processing to form carbon fibers and activated carbon fibers. The method is a wet spinning method, in which a spinning solution of lignin or lignin derivatives, cellulose carbamate and alkali lye is pressed through the holes of a nozzle and introduced directly into a coagulation bath. The precursor fiber being precipitated in the bath may be subjected to different further method steps: It may be stretched, after-treated, dried at elevated temperature and rolled up. Since it constitutes a cost-effective starting material, it may subsequently be used for producing carbon fibers and activated carbon fibers.

[0002] Carbon fibers are high-performance reinforcing fibers which have already been used for a long time for composite materials in aircraft construction, high-performance vehicle construction (Formula I, high-performance sailing vessels etc.), for sports equipment and for wind power plants. A current challenge consists in producing carbon fibers of medium quality and with low production costs at the same time, so that they may also be used in automobile manufacture. The important driving force for this is the aim of providing electric vehicles which have a low weight but nevertheless stable bodywork.

[0003] Carbon fibers are produced by heat treatment of organic precursor fibers at temperatures above 1,000.degree. C. The first industrial production of carbon fibers based on cellulose precursors was effected by the continuous method developed and patented by C. E. Ford and C. V. Mitchell (U.S. Pat. No. 3,107,152). The carbon fibers thus produced were first marketed under the trade name "Thornel 25" with strengths of 1.25 GPa and moduli of 172 GPa. Due to further developments, further carbon fibers with improved properties could be produced. They had strengths of up to 4.0 GPa and moduli of elasticity of up to 690 GPa.

[0004] Crucial for good fiber properties even then was already special process control. The cellulose fibers were exposed to temperatures of 2,500-3,000.degree. C. and deformed in the process (so-called stretch graphitization). Graphite can be plastically deformed and orientated along the fiber axis only at these high temperatures.

[0005] In the production process according to Ford and Mitchell however, only a carbon yield between 10 and 20 wt. % could be achieved. In addition, the process was also very costly at 1,000 $/kg of carbon fiber due to the special method control. This resulted in the method being uneconomical and the production of carbon fibers based on cellulose being almost completely stopped.

[0006] This development was accompanied by intensive research work in the field of carbon fibers made of alternative starting materials. It was here shown that carbon fibers based on polyacrylonitrile (PAN) or based on copolymers of polyacrylonitrile with the same property profile could be produced significantly more cost-effectively. Even today PAN and PAN copolymers are still the dominant starting materials for producing precursor filament yarns and carbon fibers generated therefrom. This includes the ultrahigh-modulus carbon fibers based on pitch. (J. P. Donnet et al., Carbon fibers, third edition, Marcel Dekker, Inc. New York, Basel, Hong Kong).

[0007] Although the production of carbon fibers on the whole has become more favorable due to the substitution of cellulose with PAN or pitch, the distribution of the production cost proportions is uneven and strongly coupled to the price of crude oil. Both PAN and pitch are completely petroleum-based. Their production and isolation accounts for about half of the production costs of carbon fibers.

[0008] It is therefore a current challenge to develop alternative methods for producing carbon fibers which are just as cost-effective or even more cost-effective and the production costs of which do not correlate to the same extent with the price of crude oil as for PAN-based carbon fibers. Lesser properties of the resulting carbon fibers could also be accepted in favor of lower production costs. In order to successfully occupy a new market segment, the carbon fiber should however have at least a modulus of elasticity of 170 GPa and a strength of 1.7 GPa.

[0009] The raw material investigated most intensively for producing an alternative precursor for carbon fibers is the biopolymer lignin. This offers the advantage of a very high carbon yield (about 60 wt. %) compared to PAN (50 wt. %) or cellulose (20-30 wt. %). Lignin is a polyaromatic polyol, which is a constituent of wood and occurs in large quantities as a byproduct of cellulose production. The chemical structure of lignin is determined by the type of wood used in the cellulose process as well as the method of cellulose digestion. The main proportion of lignin occurring is currently only used energetically. An extremely cost-effective raw material is available with lignin which is in practice not fiber-forming in unmodified form.

[0010] Kadla (J. F. Kadla et al., Carbon, 40, 2913-2920, 2002) describes by way of example one process variant for producing a lignin-based precursor fiber for a carbon fiber. A commercially available kraft lignin is processed here by melt-spinning to form a lignin fiber. However, the disadvantage of this method proved to be that a cost-intensive thermal pre-treatment of the lignin is necessary. In addition, the carbon fibers, which were produced from the melt-spun, lignin-containing precursors, had strengths of only about 0.4 GPa and moduli in the range from 40 to 50 GPa. Hence, they do not fulfil the mechanical characteristic values strived for by automobile manufacture.

[0011] Kubo (Kubo et al., Carbon, 36, 1119-1124, 1998) and Sudo (K. Sudo et al. J. Appl. Polymer Sci., 44, 127-134, 1992) disclose further processes for melt-spinning of lignin.

[0012] In the latter, the non-melting, high-molecular constituents have to be removed from the lignin in a pre-treatment step and the carbon fibers produced by these processes are likewise characterized by a low strength level and do not meet the requirements.

[0013] The state of the art thus shows that the melt-spinning of lignin-containing precursors is indeed possible in principle, but requires costly method steps. The precursor fibers were converted only discontinuously and as a monofilament to form carbon fibers by means of melt-spinning methods, since it required a crosslinking reaction of the lignin to transform the meltable precursor fibers to a no longer melting state.

[0014] The use of solutions, which contain lignin and a fiber-forming polymer, has the advantage that from the start they are thus non-melting polymers. They permit more rapid conversion and process steps for removing the meltability are not necessary.

[0015] U.S. Pat. No. 3,461,082 describes such a process for producing a lignin-containing precursor fiber. Here, a solution of a polymer, such as PAN or viscose and lignin, is processed by the dry spinning method. The spinning mass is conveyed through a spinning nozzle and the band of filaments generated then enters a spinning shaft exposed to a hot gas medium. The solvent thus evaporates and the polymers are regenerated in fiber form and may be further processed.

[0016] Once again, direct dependence on the oil price arises for the use of PAN as a fiber-forming polymer. However, the use of viscose likewise brings with it disadvantages, since viscose is cellulose xanthate and this does not constitute a storage-stable compound, since xanthate substituents may be split off at any time. This does not meet the quality requirements which a conversion process to the carbon fiber taking place subsequently places on the precursor material.

[0017] Furthermore, it has to be assumed in the dry spinning method that residues of the alkali lye used to dissolve the cellulose xanthate remain in the fiber and hence inevitably lead to defects during conversion to the carbon fiber, since the fiber may then overheat locally.

[0018] Even if the viscose process is by far the most often used method for producing cellulosic chemical fibers, the byproducts there being produced, such as for example carbon disulfide, hydrogen sulfide, heavy metals, are ecologically questionable and the entire process is associated with high investment costs. Therefore efforts have already been undertaken for years to supersede the viscose method with alternative methods.

[0019] On the one hand, methods based on the direct dissolution of cellulose in suitable, solvents, such as for example N-methylmorpholine-N-oxide or ionic liquids, have been developed for this. Cellulosic regenerated fibers containing lignin can also be generated therefrom. However, such spinning solutions have been further processed hitherto by the air-gap spinning method due to their high viscosity. The high viscosity additionally required more expensive process equipment, so that the spinning solution could be conveyed, and it was necessary to filter the solution. Recovery of the solvent has enormous significance in the direct dissolution processes of cellulose. Due to the introduction of lignin/lignin derivative into the spinning solution and the joint precipitation process, after which the polymer solution has emerged from the nozzle in fiber form, has passed the air gap and then entered the precipitation bath, there is partial washing out of the lignin/lignin derivative into the precipitation bath, into which the solvent also diffuses. The proportion of lignin/lignin derivative which transfers to the precipitation bath may be reduced by suitable additives. However, both cases constitute an additional cost for recycling of the solvent, whereby the increased process costs have to be applied to the resulting carbon fiber and thus one possible cost advantage is minimized.

[0020] EP 57 105, EP 178 292 and EP 2 110 468 describe a possibilities exists of producing mouldings made of regenerated cellulose by precipitating a solution of cellulose carbamate. Cellulose carbamate is formed by reacting cellulose with urea, is soluble in cold sodium hydroxide solution and may be regenerated in acid, salt-containing aqueous solutions or heated sodium hydroxide solution.

[0021] In addition to this way of generating regenerated fibers from cellulose carbamate, cellulose carbamate may also be transformed from NMMO by means of air-gap gap spinning, as in EP 1 716 273 B1. The structure formation of the regenerated fibers is effected in this process in the air gap and leads to high-modulus and high-strength fibers. The stability of the spinning solution made of cellulose carbamate in NMMO is problematic, since there is increased splitting of the carbamate substituents, whereby the rheological properties of the spinning solution change permanently and hence the spinning behavior. Furthermore, gaseous ammonia, which escapes through the spinning nozzle and leads to spinning instabilities, is produced as a cleavage product.

[0022] It was therefore the object of the present invention to provide a method for producing a lignin-containing precursor fiber which does not have the disadvantages of the above-mentioned methods from the state of the art. This means that the spinning solution does not contain cellulose xanthates or viscose and should be able to be processed by the wet spinning method. In addition, no costly pre-treatment steps should be necessary for producing the spinnable solution. In addition to these prerequisites, the method should be sustainable and cost-effective.

[0023] Furthermore, the object of the present invention is to indicate a corresponding lignin-containing precursor fiber which has high moduli of elasticity and strengths. In addition, the present invention relates to the further processing of the precursor fiber to form a carbon fiber as well as to a correspondingly produced carbon fiber or activated carbon fiber.

[0024] This object is achieved with regard to the method for producing a lignin-containing precursor fiber having the features of patent claim 1. Patent claim 15 relates to a correspondingly produced precursor fiber. In addition, a method for producing a carbon fiber from the precursor fiber is indicated by patent claim 19. A correspondingly produced carbon fiber is provided by patent claim 22 and patent claim 24 shows uses of this carbon fiber. The respective dependent claims show advantageous developments.

[0025] In the method of the invention for producing a lignin-containing precursor fiber for the production of carbon fibers and/or activated carbon fibers, a spinning solution containing at least one type of lignin or lignin derivative as well as a cellulose carbamate and a solvent, is extruded through a holed spinning nozzle, which is immersed in a coagulation bath, wherein the lignin-containing precursor fiber precipitates. The spinning method of the invention is thus a wet spinning method.

[0026] Storage-stable precursor fibers with high filament numbers could be generated by the method of the invention due to surprisingly simple process steps.

[0027] It is particularly advantageous in the method of the invention if the at least one type of lignin or the lignin present in the lignin derivative is extracted from a coniferous wood, deciduous wood or annual plant source, wherein the lignin particularly preferably has a weight-average molar mass distribution between 500 g/mol and 20,000 g/mol, particularly preferably between 2,000 g/mol and 10,000 g/mol, most particularly preferably between 4,000 g/mol and 10,000 g/mol. Likewise it is preferred in the method of the invention if the lignin or lignin derivative contains less than 1 wt. % of ash. This may be achieved in that the corresponding lignin or lignin derivative is washed intensively with water or optionally with acids.

[0028] Furthermore, it is advantageous if the cellulose carbamate has a DP.sub.Cuoxam determined by means of viscosimetry between 150 and 750, particularly preferably a DP.sub.Cuoxam between 250 and 550. The cellulose carbamate preferably also has a degree of substitution between 0.1 to 1.0, in particular between 0.2 and 0.6. In a further preferred embodiment of the invention, cellulose carbamate is used in a concentration of more than 6 wt. %, particularly preferably of more than 8 wt. %, most particularly preferably of more than 10 wt. %, relative to the spinning solution. A nitrogen content of the precursor fiber, which has an advantageous effect in the further processing of the fiber to form a carbon fiber, is produced in this manner. Furthermore, it is preferred that the spinning solution has a mass ratio of cellulose carbamate to the at least one type of lignin or lignin derivative between 0.60 and 1.80, particularly preferably between 0.80 and 1.20, most particularly preferably 1.00. In one embodiment of the invention, the solvent is selected from the group consisting of [0029] alkali lyes, in particular sodium hydroxide or potassium hydroxide; [0030] tertiary amine oxides, in particular N-methylmorpholine N-oxide; [0031] ionic liquids, preferably selected from the group consisting of imidazolium compounds, pyridinium compounds or tetraalkyl-ammonium compounds, particularly preferably 1-butyl-3-methyl-imidazolium chloride, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate; and/or [0032] mixtures thereof.

[0033] It is particularly preferred that the solvent consists exclusively of alkali lyes, tertiary amine oxides, in particular N-methylmorpholine N-oxide, and that the solvent does not contain ionic liquids.

[0034] This has the advantage that there may be no undesirable side reactions of the ionic liquid itself or of the ionic liquid with the degradation products with cellulose carbamate. It may be successfully avoided that an imidazolium cation of an ionic liquid or degradation products thereof react with the reducing end of the cellulose unit or/and other aldehyde groups along the cellulose carbamate with formation of a C--C bond and that this undefined substitution has an influence on the cellulose carbamate/cellulose carbamate or cellulose carbamate/lignin interaction in the precursor fiber formed. By excluding the ionic liquids from the spinning solution, it may furthermore be prevented that there is formation of disadvantageous temperature profiles in the fiber.

[0035] Furthermore, it is particularly preferred that the spinning solution consists of at least one type of lignin or lignin derivative as well as a cellulose carbamate and a solvent and that it contains no ionic liquids, no cellulose, no further cellulose derivatives and no other additives.

[0036] Furthermore, it is preferred for the method that the spinning solution contains spinning auxiliaries selected from the group consisting of inorganic substances, in particular ZnO, organic additives, in particular quaternary ammonium compounds (cationic, for example Berol Spin 641), alkyl ethers of polyoxyethylene glycol (non-ionic, for example Berol Visco 32) or sulfonated oils (anionic), or mixtures thereof.

[0037] The spinning solution may be produced by stirring or kneading the at least one type of lignin or lignin derivative as well as cellulose carbamate in the solvent at a temperature of less than 5.degree. C., preferably of less than 0.degree. C. Stirring or kneading is thus continued until the solution is homogeneous and fiber-free. The spinning solution thus produced is filtered before extrusion through the holed spinning nozzle into the coagulation bath. Optionally present insoluble constituents may thus be separated off.

[0038] In a preferred embodiment, the holed spinning nozzle has a spinning hole diameter of 50 to 500 .mu.m, particularly preferably 50 to 100 .mu.m.

[0039] A further advantageous aspect of the method of the invention makes provision that the coagulation bath preferably has a pH value between 1 and 7, particularly preferably between 2 and 5. The temperature of the spinning bath is preferably 5.degree. C. to 60.degree. C., particularly preferably 10 to 50.degree. C.

[0040] Furthermore, the coagulation bath, in which the fiber precipitates after extrusion through the spinning nozzle, may preferably contain water and/or a solvent selected from the group of alcohols, saturated or unsaturated hydrocarbons, polar-aprotic compounds, particularly preferably DMF, DMSO, DMAc, or mixtures thereof, in particular in a proportion between 10 and 50 vol. % or water, add, particularly preferably sulfuric acid, and salts, particularly preferably selected from the group of sulfates, chlorides, salts with lithium, sodium, potassium, caesium, ammonium, magnesium, calcium, zinc, copper, nickel, cadmium, or mixtures thereof as a cation, preferably in a concentration between 40 and 240 g/L, particularly preferably in a concentration between 60 and 240 g/L.

[0041] The composition of the coagulation bath thus preferably depends on the composition of the spinning solution. If the spinning solution contains polar, aprotic additives, such as for example DMSO, DMF, DMAc, for viscosity regulation, the spinning bath is preferably composed of water and/or alcohols, saturated or unsaturated hydrocarbons, polar-aprotic compounds, particularly preferably DMF, DMSO, DMAc, or mixtures thereof.

[0042] If spinning is carried out from an alkaline aqueous solution, the spinning bath is preferably composed of water and/or sulfuric acid and salt.

[0043] It is further preferred that the precursor fiber precipitated in the coagulation bath is then introduced into a stretching bath and stretched to 110 to 500%, preferably to 110 to 300%, of its length, wherein the stretching bath contains water, air, or a mixture of water and a solvent, preferably at a temperature of more than 60.degree. C., particularly preferably at a temperature of more than 80.degree. C., most particularly preferably at a temperature of more than 100.degree. C., or consists thereof, that the precursor fiber washed using distilled water, dried by heated rollers and/or by through-flow drying at a temperature between 40 and 100.degree. C., preferably between 60 and 80.degree. C., and/or rolled up.

[0044] The extent of structural orientation, which is achieved by stretching the precursor fiber, is thus unexpectedly high and contributes to the extraordinarily good mechanical properties of the resulting carbon fiber. In a further preferred variant of the method of the invention, the precursor fiber is coated with a spinning oil before and/or after it is dried.

[0045] Equally, it is preferred in the process if the precursor fiber during stabilization is present in the form of a continuous multi-filament yarn and the latter is continuously transported through an oven. Hence, the precursor fibers may be transferred to a non-meltable and non-combustible state at residence times between 10 to 100 minutes and oven temperatures between 100 and 350.degree. C. By applying a mechanical tension, furthermore, extension of the precursor fiber may be achieved and at the same time it is prevented that the fiber sags loosely in the oven.

[0046] According to the invention, a precursor fiber for producing carbon fibers is likewise indicated. The precursor fiber of the invention is characterized by a content of at least one type of lignin or lignin derivative of more than 5 wt %, preferably more than 10 wt. %, particularly preferably between 30 and 80 wt % and has a strength measured according to DIN 53 834 of at least 5 cN/tex, preferably of at least 10 cN/tex, particularly preferably of at least 15 cN/tex, most particularly preferably of at least 20 cN/tex, as well as a modulus of elasticity of 350 cN/tex, preferably of at least 550 cN/tex, most preferably of at least 750 cN/tex.

[0047] The precursor fibers of the invention surprisingly withstand very high heating rates of up to 50.degree. C./minute which are applied during stabilization of the precursor fiber. In addition, they have an unexpectedly high carbon yield after carbonization to form carbon fibers. Also the loop strength, buckling strength and tensile strength, which lies in the range from 150 to 200 MPa, and their extension at break properties are remarkable and surpass the corresponding properties of comparable lignin precursor fibers from the state of the art.

[0048] The precursor fiber according to the preceding claim preferably has a nitrogen/carbon mass ratio of less than 0.06, particularly preferably less than 0.04, most particularly preferably less than 0.02.

[0049] It is additionally preferred if the precursor fiber has a round cross-section with a diameter of less than 70 .mu.m.

[0050] The precursor fiber of the invention can be particularly advantageously produced by a method described above.

[0051] According to the invention, likewise a method for producing a carbon fiber is disclosed, in which the precursor fiber is stabilized at temperatures between 100 and 300.degree. C. and simultaneously is extended in the range between 0 and 300% relative to its initial length, wherein the precursor fiber becomes non-meltable and non-combustible and obtains an orientated structure.

[0052] Then the stabilized, orientated precursor fiber may be pre-carbonized at temperatures between 300 and 900.degree. C. and may be extended in the range between 0 and 300% relative to its initial length, wherein a carbon proportion of the fiber of more than 80 wt. % and an orientated structure are obtained.

[0053] Optionally the carbon fiber thus obtained may also be graphitized at temperatures of 2,000-3,000.degree. C.

[0054] In addition, the present invention provides a carbon fiber from a lignin-containing precursor fiber which contains a carbon proportion of more than 80 wt. %, preferably of more than 90 wt. %.

[0055] In addition, the carbon fiber of the invention can advantageously be produced by the previously described method for producing a carbon fiber.

[0056] Furthermore, it is the object of the invention that the carbon fiber, which was produced by the previously described method for producing a carbon fiber, is used for producing a chemically activated carbon fiber and/or for producing composite materials.

[0057] The carbonized or graphitized carbon fiber may thus be activated physically or chemically by heat treatment in oxidizing atmosphere or plasma treatment or treatment with chemicals on the surface.

EXAMPLE 1

[0058] 250 g of cellulose carbamate {DPCuox 258, N content 2.2%, moisture content 10 wt. %}was dissolved together with 2,000 g of a 7 wt. % aqueous sodium hydroxide solution chilled at -4.degree. C. with stirring within 90 minutes. 250 g of a kraft lignin {moisture content 10 wt. %) were then added to the solution and the mixture was stirred for a further 30 minutes. The solution was then filtered chilled under exposure to pressure by means of nitrogen (2 bar) through a 10 .mu.m metal filter and for the dissolution stored for 20 hours.

[0059] The low-viscosity spinning solution thus generated was conveyed at a temperature of +5.degree. C. by means of a spinning pump to the spinning nozzle (600 hole, 70 .mu.m), which projected into an aqueous spinning bath tempered at 40.degree. C. comprising 80 g/l of sulfuric acid and 140 g/l of sodium sulfate. The coagulated filaments were drawn off by means of a nozzle draft of 0.7 and fed to washing. The filaments were washed by means of distilled water heated at 60.degree. C. and dried at 80.degree. C. The filaments thus generated had a strength of 19 cN/tex, an extension of 6% as well as a modulus of 923 cN/tex. The lignin content of the filaments was 49 wt. %.

EXAMPLE 2

[0060] The continuous multi-filament yarn produced by the method from Example 1, consisting of lignin and cellulose carbamate (50/50 mass %), was transported continuously through two tubular ovens separated spatially from one another and exposed to heat. In the first tubular oven through which air flows continuously, the process of stabilization was carried out on the multi-filament yarn and for this temperatures in the range from 100-300.degree. C. and action times at corresponding temperatures of about 80 minutes were applied. Due to different rates of the thread transport devices upstream and downstream of the tubular oven, an extension of the multi-filament yarn of 100% was realized during the action of heat. The structure of the fiber material is thus orientated and thus mechanical properties of the final C fibers significantly improved. The resulting orientated and stabilized continuous multi-filament yarn was then wound onto a bobbin core. The corresponding multi-filament yarn is characterized by non-meltability, non-combustibility, freedom from adhesion adequate loop strength and buckling strength as well as tensile strength of about 200 MPa and extensions at break of about 5%. In the second tubular oven through which inert gas flows continuously, the process of pre-carbonization was carried out and for this temperatures in the range from 300-900.degree. C. and action times at corresponding temperatures of 30 minutes applied. Due to different rates of the thread transport devices upstream and downstream of the oven, an extension of the multi-filament yarn of about 10% could be realized during the action of heat. The resulting orientated and pre-carbonized continuous filament yarn was then wound onto a bobbin core. The corresponding multi-filament yarn is characterized by a carbon proportion >80 wt. %. Finally, the process of carbonization was effected in a further oven at temperatures of 900-1,600.degree. C., wherein an orientated carbonized multi-filament yarn was obtained which is characterized by a carbon proportion >90 wt. %.

EXAMPLE 3

[0061] 300 g of cellulose carbamate (DPCuox: 274, DS 0.3) are mixed together with 300 g of Organosolv Lignin with 1,500 g of ethylmethylimidazolium acetate as well as 500 g of dimethyl sulfoxide and dissolved in a horizontal kneader at 110.degree. C. within 2.5 hours. The resulting homogeneous, black solution is completely fiber-free and has a viscosity of 65 Pa s at 50.degree. C.

[0062] The filtered solution was conveyed by means of pressure and gear pump through a 120-hole spinning nozzle (hole diameter 70 .mu.m) in a 10 vol. % aqueous coagulation bath containing ethylmethylimidazolium acetate and precipitated. The filaments were washed by means of distilled water heated at 60.degree. C. and dried at 80.degree. C. The filaments thus generated had a strength of 24 cN/tex, an extension of 8% as well as a modulus of 1,150 cN/tex. The lignin content of the filaments was 41 wt. %.

EXAMPLE 4

[0063] The continuous multi-filament yarn produced by the method from Example 3, consisting of lignin and cellulose carbamate (50/50 mass %), was transported continuously through a tubular oven and exposed to heat. During this process step (stabilization), the multi-filament yarn was exposed in air atmosphere to temperatures in the range from 100-300.degree. C. and action times at corresponding temperatures of about 80 minutes. The multi-filament yarn produced according to Example 3 could be extended during the action of heat but only by 10% at most, whereby the structure of the fiber material was orientated only inadequately. After the subsequent process steps of pre-carbonization and carbonization (analogously to Example 2), the mechanical properties of the final C fibers based on the multi-filament yarn produced according to Example 3 were only a fraction of the level which was achieved with multi-filament yarns from Example 1.

Claims

1-24. (canceled)

25. A method for producing a lignin-containing precursor fiber for the production of carbon fibers and/or activated carbon fibers, wherein a spinning solution containing A) at least one type of lignin or lignin derivative , B) a cellulose carbamate, and C) a solvent, is extruded through a holed spinning nozzle immersed in a coagulation bath, wherein the lignin-containing precursor fiber precipitates.

26. The method according to claim 25, wherein the at least one type of lignin or the lignin present in the lignin derivative is extracted from a coniferous wood, deciduous wood, or annual plant source.

27. The method according to claim 25, wherein the lignin has a weight-average molar mass between 500 g/mol and 20,000 g/mol.

28. The method according to claim 25, wherein the cellulose carbamate has a DP.sub.Cuoxam determined by viscosimetry between 150 and 750, wherein the cellulose carbamate has a degree of substitution between 0.1 and 1.0.

29. The method according to claim 25, wherein the cellulose carbamate is present in a concentration of more than 6 wt. %, relative to the spinning solution.

30. The method according to claim 25, wherein the solvent is selected from the group consisting of alkali lyes; tertiary amine oxides; ionic liquids selected from the group consisting of imidazolium compounds, pyridinium compounds, and tetraalkyl-ammonium compounds; and mixtures thereof.

31. The method according to claim 25, wherein the spinning solution has a mass ratio of cellulose carbamate to the at least one type of lignin or lignin derivative between 0.60 and 1.80.

32. The method according to claim 25, wherein the spinning solution is produced by stirring or kneading the at least one type of lignin or the lignin derivative as well as the cellulose carbamate in the solvent at a temperature of less than 0.degree. C.

33. The method according to claim 25, wherein the spinning solution further contains spinning auxiliaries selected from the group consisting of inorganic substances, organic additives, and mixtures thereof.

34. The method according to claim 25, wherein the spinning solution is filtered before extrusion through the holed spinning nozzle into the coagulation bath.

35. The method according to claim 25, wherein the holed spinning nozzle has a spinning hole diameter of 50 to 500 .mu.m.

36. The method according to claim 25, wherein the coagulation bath has a pH value between 1 and 7.

37. The method according to claim 25, wherein the coagulation bath contains water and/or a solvent selected from alcohols, saturated or unsaturated hydrocarbons, polar-aprotic compounds, water, acid, acid salt, and mixtures thereof

38. The method according to claim 25, which further includes: the precursor fiber precipitated in the coagulation bath is introduced into a stretching bath and stretched to 110 to 500% of its length, wherein the stretching bath contains water, air, or a mixture of water and a solvent, (ii) the precursor fiber from (i) is washed with distilled water, (iii) the precursor fiber from (ii) is dried by heated rollers and/or by through-flow drying at a temperature between 40 and 100.degree. C., and/or (iv) the precursor fiber from (ii) or (iii) is rolled up.

39. The method according to claim 38, wherein the precursor fiber is coated with a spinning oil before and/or after it is dried in step (iii).

40. A precursor fiber having more than 5 wt. % of the at least one type of lignin or lignin derivative, wherein the pre-cursor fiber has a strength measured according to DIN 53 834 of at least 5 cN/tex and a modulus of elasticity of 350 cN/tex.

41. The precursor fiber according to claim 40, wherein the precursor fiber has a nitrogen/carbon mass ratio of less than 0.06.

42. The precursor fiber according to claim 40, wherein the precursor fiber has a round cross-section with a diameter of less than 70 .mu.m.

43. A precursor fiber produced by the method of claim 25.

44. A method for producing a carbon fiber, in which a precursor fiber according to claim 40 is stabilized at temperatures between 100 and 300.degree. C., pre-carbonized between 300 and 900.degree. C., and carbonized between 900 and 2,000.degree. C. under inert conditions.

45. The method according to claim 44, wherein the precursor fiber is stabilized at temperatures between 100 and 300.degree. C. and simultaneously is extended in the range between 0 and 300% relative to its initial length, whereby the precursor fiber becomes non-meltable and non-combustible and obtains an orientated structure.

46. The method according to claim 44, wherein the stabilized, orientated precursor fiber is pre-carbonized at temperatures between 300 and 900.degree. C. and extended in the range between 0 and 300% relative to its initial length, thereby obtaining a carbon proportion of more than 80 wt. % and an orientated structure.

47. A carbon fiber made from a lignin-containing precursor fiber, containing a carbon proportion of more than 80 wt.

48. The carbon fiber produced by the method of claim 44.