Amidines as initiators for converting acrylic fibers into carbon fibers

Abstract

A method of preparing PANOX fibers useful in the production of superior carbon fiber material; the method based on the concept that the true initiators in the preparation of superior carbon fiber are amidines.

1 . A precursor fiber for preparing carbon fiber comprising a chemically treated solid acrylonitrile polymer wherein the polymer comprises cyano and amidine pendant groups and wherein the amidine groups are present in an amount of about 1-10 mole percent, based on total amount of functional groups.  
   
   
       2 . A precursor fiber according to  claim 1  wherein the chemically treated solid acrylonitrile polymer is the reaction product of solid polyacrylonitrile and a nitrogen-containing compound, the nitrogen-containing compound being in the liquid or gaseous state.  
   
   
       3 . A precursor fiber according to  claim 2  wherein the nitrogen-containing compound is a member selected from the group consisting of a primary amine, a secondary amine, ammonia, and mixtures thereof.  
   
   
       4 . A precursor fiber according to  claim 3  wherein the primary amine is a member selected from the group consisting of methyl amine, ethyl amine, n-propyl amine, isopropyl amine, ethanol amine, and mixtures thereof.  
   
   
       5 . A precursor fiber according to  claim 3  wherein the secondary amine is a member selected from the group consisting of dimethyl amine, diethyl amine, methylethyl amine, di(n-propyl) amine, diisopropylamine, diethanol amine, methyl (n-propyl) amine, ethyl (n-propyl) amine, methyl (isopropyl) amine, ethyl (isopropyl) amine, and mixtures thereof.  
   
   
       6 . A precursor fiber according to  claim 2  wherein the solid acrylonitrile polymer is a member selected from the group consisting of a solid polyacrylonitrile homopolymer and a solid polyacrylonitrile copolymer.  
   
   
       7 . A precursor fiber according to  claim 6  wherein the solid polyacrylonitrile copolymer is prepared from acrylonitrile monomer and a co-monomer selected from the group consisting of itaconic acid, acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, p-vinyl benzoic acid, itaconic anhydride, and mixtures thereof.  
   
   
       8 . A precursor fiber according to  claim 7  wherein the solid polyacrylonitrile copolymer is a terpolymer where a third monomer is a member selected from the group consisting of alkyl acrylates having 1-4 carbon atoms in the alkyl group, alkyl methacrylates having 1-4 carbon atoms in the alkyl group, vinyl acetate, vinyl propinate, styrene, vinyl chloride, vinylidene chloride, and mixtures thereof.  
   
   
       9 . A process of making a precursor fiber for preparing carbon fiber comprising: 
 (a) preparing a suspension of a solid acrylonitrile polymer in a solvent;    (b) adding to the suspension a liquid or gaseous chemical treating agent which is a member selected from the group consisting of a primary organic amine, a secondary organic amine, ammonia and mixtures thereof;    (c) spinning the suspension to obtain a fiber;    (d) heating the fiber to obtain a precursor which comprises a chemically treated solid acrylonitrile polymer wherein the treated polymer comprises cyano and amidine pendant groups; and    (e) separating the precursor fiber from the suspension whereby the precursor fiber contains amidine groups in an amount of about 1-10 mole percent, based on total amount of functional groups.    
   
   
       10 . A process according to  claim 9  wherein the solid acrylonitrile polymer is a member selected from the group consisting of an acrylonitrile homopolymer and an acrylonitrile copolymer.  
   
   
       11 . A process according to  claim 11  wherein the acrylonitrile copolymer is prepared 
 from acrylonitrile monomer and a co-monomer selected from the group consisting of itaconic acid, acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, p-vinyl benzoic acid, itaconic anhydride, and mixtures thereof.    
   
   
       12 . A process for making a precursor fiber for preparing carbon fiber comprising: 
 (a) placing in a heating zone a fiber comprising an acrylonitrile copolymer comprising at least 90 mole percent acrylonitrile units, and about 1 mole percent to about 10 mole percent nitrogen-containing compound as neutralizing cation for carboxylate groups, said compound incorporated into the polymer by copolymerization of one or more copolymerizable, carboxylate containing co-monomers;    (b) heating the fiber in air at a temperature of about 200° C. to about 250° C. for a time of about 3 minutes to about 15 minutes; and    (c) withdrawing a precursor fiber wherein the precursor fiber contains amidine groups in an amount of about 1-10 mole percent, based on total amount of functional groups.    
   
   
       13 . A method of selecting a precursor fiber for preparing a carbon fiber, the method comprising the steps of: 
 (a) obtaining a fiber comprising a chemically treated solid acrylonitrile polymer which is the reaction product of solid polyacrylonitrile and a nitrogen-containing compound, the nitrogen-containing compound being in the liquid or gaseous state,    (b) analyzing the fiber by means of an infrared spectrophotometer;    (c) removing the fiber to a heating zone;    (d) heating the fiber in air at a temperature of about 250° C. to about 275° C. for a time of about 3-10 minutes;    (e) withdrawing the fiber from the heating zone;    (f) cooling the fiber;    (g) analyzing the cooled fiber by means of an infrared spectrophotometer;    (h) calculating the amount of reduction of nitrile absorbance based on the IR scans of the original unheated fiber and the heated fiber; and    (i) selecting the fiber for preparing carbon fiber when the nitrile absorbance is reduced by about 15% to about 25%.    
   
   
       14 . A method according to  claim 13  wherein the nitrogen-containing compound is a member selected from the group consisting of a primary amine, a secondary amine, ammonia and mixtures thereof.  
   
   
       15 . A method according to  claim 14  wherein the primary amine is a member selected from the group consisting of methyl amine, ethyl amine, n-propyl amine, isopropyl amine, ethanol amine, and mixtures thereof.  
   
   
       16 . A method according to  claim 13  wherein the secondary amine is a member selected from the group consisting of dimethyl amine, diethyl amine, methylethyl amine, di(n-propyl) amine, diisopropylamine, diethanol amine, methyl (n-propyl) amine, ethyl (n-propyl) amine, methyl (isopropyl) amine, ethyl (isopropyl) amine, and mixtures thereof.  
   
   
       17 . A method according to  claim 13  wherein the solid acrylonitrile polymer is a member selected from the group consisting of a solid polyacrylonitrile homopolymer and a solid polyacrylonitrile copolymer.  
   
   
       18 . A method according to  claim 17  wherein the polyacrylonitrile copolymer is prepared from acrylonitrile monomer and a co-monomer selected from the group consisting of itaconic acid, acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, p-vinyl benzoic acid, itaconic anhydride, and mixtures thereof.  
   
   
       19 . A method according to  claim 18  wherein the polyacrylonitrile copolymer is a terpolymer where a third monomer is a member selected from the group consisting of alkyl acrylates having 1-4 carbon atoms in the alkyl group, alkyl methacrylates having 1-4 carbon atoms in the alkyl group, vinyl acetate, vinyl propinate, styrene, vinyl chloride, vinylidene chloride, and mixtures thereof.