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.

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 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 μm. 
     
     
         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 μm. 
     
     
         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 .