Method and formulation for preparing lignin fibres

Abstract

A formulation for melt-preparation of lignin-based fibres, which are precursors of carbon fibres. The formulation includes lignin, a plasticiser and a cross-linking agent capable of cross-linking with the lignin at a temperature at least 10° C. higher than the glass-transition temperature of the intimate blend of the lignin and the plasticizer. A method for preparing lignin-based fibres using this formulation includes the hot extrusion spinning of an intimate blend of the components of the formulation, under adequate conditions for cross-linking the cross-linking agent and the lignin in the terminal area of the extrusion device used.

What is claimed is: 
     
         1 . A method for melt-preparation of lignin-based fibers, comprising:
 a/ the intimate blending of the components of a formulation comprising:
 lignin, 
 a plasticizer miscible with said lignin, 
 and a cross-linking agent capable of cross-linking with said lignin, 
   in conditions in which no cross-linking of the cross-linking agent and of the lignin occurs,   b/ the spinning of the intimate blend thus obtained in a hot extrusion device comprising an extrusion head in a terminal part, in order to form continuous threads, by application in said extrusion device of conditions such that:
 the temperatures applied in said extrusion device are higher than the glass-transition temperature of said intimate blend, 
 and the temperatures, the residence time of said intimate blend in said extrusion device and the residence time of said intimate blend in said extrusion head are such that the cross-linking reaction of the cross-linking agent and lignin is initiated only in the extrusion head, 
   c/ when appropriate, the drawing of the threads obtained in order to form lignin-based fibers of great length,   with the cross-linking agent being chosen in such a way that the cross-linking reaction thereof with said lignin is initiated in a time less than said residence time of said intimate blend in said extrusion head at temperatures above a temperature at least 10° C. greater than the glass-transition temperature of said intimate blend of said lignin and of said plasticizer.   
     
     
         2 . The method according to  claim 1 , wherein the step a/ of intimate blending of the components of said formulation comprises the following sub-steps:
 a1/ preparation of said formulation, by blending of said lignin, said plasticizer and said cross-linking agent,   a2/ the blending by extrusion of the components of said formulation, at a temperature greater than the glass-transition temperature of the lignin and than a softening temperature of the plasticizer, in order to form an extrudate in which the lignin, the plasticizer and the cross-linking agent are in an intimate blend.   
     
     
         3 . The method according to  claim 1 , wherein the step b/ of spinning of the intimate blend of the components of the formulation, it is applied in the extrusion head a temperature that is greater than the glass-transition temperature of said intimate blend by a value of between 10 and 150° C. 
     
     
         4 . The method according to  claim 1 , wherein the lignin and the plasticizer are such, and in proportions such, that the glass-transition temperature of said intimate blend of said lignin and of said plasticizer is between 0 and 180° C. 
     
     
         5 . Method according to  claim 1 , wherein the lignin has a weight average molecular weight between 1,000 and 100,000 g/mol. 
     
     
         6 . Method according to  claim 1 , wherein the plasticizer is a polymer, or blend of polymers. 
     
     
         7 . Method according to  claim 1 , wherein the plasticizer is a fusible acrylonitrile polymer. 
     
     
         8 . Method according to  claim 1 , wherein the plasticizer has a glass-transition temperature, where applicable glass-transition temperatures, of less than 150° C. 
     
     
         9 . Method according to  claim 1 , wherein the cross-linking agent is chosen in the group consisting of:
 benzoxazines, epoxies, oxazolines, polyoxymethylenes, aldehydes, hexamethylenetetramine and hexamethylenemethoxymelamine;   compounds that have a functionality greater than or equal to two, of which the chemical functions are chosen in the group consisting of the functions: benzoxazine, epoxy (glycidyl ether in particular), isocyanate, anhydride, carboxylic acid, methylol and ester, with these chemical functions being identical or different,   or any blend of such compounds.   
     
     
         10 . Method according to  claim 1 , wherein the cross-linking agent is capable of initiating a cross-linking reaction with the lignin in less than 10 minutes at a temperature between 30 and 190° C. 
     
     
         11 . Method according to  claim 1 , wherein the cross-linking agent is capable of cross-linking with the lignin at ambient temperature. 
     
     
         12 . Method according to  claim 1 , wherein said formulation comprises the following percentages by weight, with respect to the total weight of the formulation:
 50 to 98% of lignin,   and/or 1 to 49% of plasticizer,   and/or 1 to 25%, preferably 2 to 10%, preferentially 2.5 to 5%, of cross-linking agent.   
     
     
         13 . Method according to  claim 1 , wherein said formulation comprises one or several additives chosen in the group consisting of carbon fillers of nanometric size, alone or in a mixture. 
     
     
         14 . Method according to  claim 1 , wherein a final step of storage of said lignin-based fiber at ambient temperature. 
     
     
         15 . Formulation for the implementing of a method of melt-preparation of lignin-based fibers according to  claim 1 , comprising:
 lignin that is not chemically modified,   a plasticizer miscible with said lignin,   and a cross-linking agent capable of initiating a cross-linking reaction with said lignin in less than 10 minutes at temperatures above a temperature at least 10° C. greater than the glass-transition temperature of said intimate blend of said lignin and of said plasticizer.   
     
     
         16 . Formulation according to  claim 15 , wherein the plasticizer is a fusible acrylonitrile polymer. 
     
     
         17 . Lignin-based extrudate obtained at the end of the step a/ of intimate blending of the components of the formulation of a method according to  claim 1 . 
     
     
         18 . Lignin-based fiber obtainable by a method according to  claim 1 , having a length greater than or equal to 1 m. 
     
     
         19 . A method for the manufacture of carbon fibers, comprising a step of using a lignin-based fiber according to  claim 18 . 
     
     
         20 . Method for the manufacture of a carbon fiber, comprising:
 1/ the melt-preparation of lignin-based fiber, comprising:   a/ the intimate blending of the components of a formulation comprising:
 lignin, 
 a plasticizer miscible with said lignin, 
 and a cross-linking agent capable of cross-linking with said lignin, 
   in conditions in which no cross-linking of the cross-linking agent and of the lignin occurs,   b/ the spinning of the intimate blend thus obtained in a hot extrusion device comprising an extrusion head in a terminal part, in order to form continuous threads, by application in said extrusion device of conditions such that:
 the temperatures applied in said extrusion device are higher than the glass-transition temperature of said intimate blend, 
 and the temperatures, the residence time of said intimate blend in said extrusion device and the residence time of said intimate blend in said extrusion head are such that the cross-linking reaction of the cross-linking agent and lignin is initiated only in the extrusion head, 
   c/ when appropriate, the drawing of the threads obtained in order to form lignin-based fibers of great length,   with the cross-linking agent being chosen in such a way that the cross-linking reaction thereof with said lignin is initiated in a time less than said residence time of said intimate blend in said extrusion head at temperatures above a temperature at least 10° C. greater than the glass-transition temperature of said intimate blend of said lignin and of said plasticizer; and   2/subjecting the lignin-based fiber thus obtained to a carbonization treatment.   
     
     
         21 . Method for the manufacture of a carbon fiber according to  claim 20 , wherein said lignin-based fiber is not subjected to any heat treatment step prior to the implementing of the carbonization treatment. 
     
     
         22 . Method for the manufacture of a carbon fiber according to  claim 20 , wherein prior to the treatment of said lignin-based fiber by carbonization, a step of heat treating said lignin-based fiber during a period between 10 and 60 minutes.