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.

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 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 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 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 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 C., pre-carbonized between 300 and 900 C., and carbonized between 900 and 2,000 C. under inert conditions.

45. The method according to claim 44, wherein the precursor fiber is stabilized at temperatures between 100 and 300 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 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.

Description

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 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 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 C. by means of a spinning pump to the spinning nozzle (600 hole, 70 m), which projected into an aqueous spinning bath tempered at 40 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 C. and dried at 80 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 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 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 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 C. within 2.5 hours. The resulting homogeneous, black solution is completely fiber-free and has a viscosity of 65 Pa s at 50 C.

[0062] The filtered solution was conveyed by means of pressure and gear pump through a 120-hole spinning nozzle (hole diameter 70 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 C. and dried at 80 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 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.