Process of Making Polyacrylontrile Fibers

Abstract

A process for preparing a PANOX fiber comprising: obtaining an acrylonitrile copolymer, wherein the copolymer contains at least about 2% by weight itaconic acid comonomer; forming a spin dope from the copolymer; wet spinning the spin dope to obtain gelled filaments; contacting the gelled filaments with ammonia activator in an aqueous imbibation bath; bundling the gelled filaments to obtain a fiber; removing solvent from the fiber; drawing the fiber; densifying the fiber by heating the fiber up to about 400 degrees C. for a time of about 15 minutes in a rapid densification zone; and withdrawing a PANOX fiber from the densification zone.

1 . (canceled) 
     
     
         2 . A PANOX fiber prepared according to the process comprising:
 (a) obtaining an acrylonitrile copolymer, wherein the copolymer comprises about 92% by weight to about 98% by weight acrylonitrile monomer and about 2% by weight to about 8% by weight vinyl carboxylic acid monomer, and wherein the acrylonitrile copolymer is substantially free of components selected from the group consisting of metals, metal ions and vinyl sulfonic acid monomers;   (b) adding the acrylonitrile copolymer to a solvent which is a member selected from the group consisting of DMF and DMAC to obtain an emulsion;   (c) adding the emulsion to a wet spinning zone, wherein the wet spinning zone comprises a die plate;   (d) spinning the emulsion through the die plate to obtain gelled filaments, wherein the gelled filaments have a substantially circular cross-section;   (e) adding the gelled filaments to an aqueous imbibation bath, wherein the filaments are under minimum tension, and wherein the aqueous imbibation bath comprises an activator which is a member selected from the group consisting of low molecular weight primary amine, low molecular weight secondary amine and ammonia;   (f) imbibing the gelled filaments with the activator to obtain activator-loaded gelled filaments;   (g) withdrawing the activator-loaded gelled filaments from the aqueous imbibation bath;   (h) bundling the activator-loaded gelled filaments to obtain an activator-loaded fiber;   (j) adding the activator-loaded fiber to a solvent extraction zone comprising an aqueous draw bath and a device for drawing the fiber, wherein solvent is removed from the activator-loaded fiber;   (k) drawing the activator-loaded fiber to about 7× to about 9× while in the aqueous draw bath to obtain a drawn fiber, wherein the drawn fiber has a density of about 1.18 grams per cubic centimeter;   (l) adding the drawn fiber to a rapid densification unit; and   (m) heating the drawn fiber for about 8 minutes to about 15 minutes, wherein the heating is conducted by employing a heating cycle beginning at about 190 degrees C. and ending at about 400 degrees C., to obtain the PANOX fiber, wherein the density of the PANOX fiber is in the range of about 1.40 grams per cubic centimeter to about 1.5 grams per cubic centimeter.   
     
     
         3 .- 12 . (canceled) 
     
     
         13 . An apparatus for preparing PANOX fiber comprising:
 (a) a spin dope formation unit;   (b) a spinning unit;   (c) an aqueous imbibation unit;   (d) a solvent extraction unit;   (e) a rapid densification unit;   (f) a first transfer means operatively connecting the spin dope formation unit to the spinning unit,   (g) a second transfer means operatively connecting the spinning unit to the aqueous imbibation unit;   (h) a third transfer means operatively connecting the aqueous imbibation unit to the solvent extraction unit; and   (j) a fourth transfer means operatively connecting the solvent extraction unit to the rapid densification unit.   
     
     
         14 . The apparatus according to  claim 13  wherein the aqueous imbibation bath comprises water and an activator which is a member selected from the group consisting of a low molecular weight primary amine, a low molecular weight secondary amine and ammonia. 
     
     
         15 . The apparatus according to  claim 13  wherein the rapid densification unit comprises a set of three heating rolls. 
     
     
         16 . The apparatus according to  claim 15  wherein the set of three heating rolls comprises a first heating roll maintained at a temperature of about 235 degrees C. to about 245 degrees C., a second heating roll maintained at a temperature of about 245 degrees C. to about 255 degrees C., and a third heating roll maintained at a temperature of about 255 degrees C. to about 265 degrees C. 
     
     
         17 . The apparatus according to  claim 16  wherein the first heating roll is maintained at a temperature of about 240 degrees C., the second heating roll is maintained at a temperature of about 250 degrees C., and the third heating roll is maintained at a temperature of about 260 degrees C. 
     
     
         18 . The apparatus according to  claim 13  wherein the spinning unit comprises a wet spinning unit. 
     
     
         19 . The apparatus according to  claim 13  wherein the solvent extraction unit comprises an aqueous wash bath and a device for drawing a fiber.