Thermal Insulators and Methods Thereof

Abstract

The provided articles and methods use a non-woven fibrous web containing 60-100 wt % of oxidized polyacrylonitrile fibers; and 0-40 wt % of reinforcing fibers having outer surfaces comprised of a polymer with a melting temperature of from 100° C. to 300° C. The non-woven fibrous web has an average bulk density of from 15 kg/m3 to 50 kg/m3, with the plurality of fibers substantially entangled along directions perpendicular to a major surface of the non-woven fibrous web. Optionally, the oxidized polyacrylonitrile fibers can have a crimped configuration. Advantageously, these articles can display a combination of low thermal conductivity, high tensile strength, and flame resistance.

1 . A thermal insulator comprising:
 a non-woven fibrous web comprising a plurality of fibers, the plurality of fibers comprising:
 60-100 wt % of oxidized polyacrylonitrile fibers; and 
 0-40 wt % of reinforcing fibers having an outer surface comprised of a polymer with a melting temperature of from 100° C. to 300° C., 
   wherein the non-woven fibrous web has an average bulk density of from 15 kg/m 3  to 50 kg/m 3  and wherein the plurality of fibers are substantially entangled along directions perpendicular to a major surface of the non-woven fibrous web.   
     
     
         2 . The thermal insulator of  claim 1 , wherein the non-woven fibrous web contains 3-19 wt % of reinforcing fibers having an outer surface comprised of a polymer with a melting temperature of from 100° C. to 300° C. 
     
     
         3 . The thermal insulator of  claim 1 , wherein the oxidized polyacrylonitrile fibers represent over 85 vol % of the plurality of fibers that are not reinforcing fibers. 
     
     
         4 . The thermal insulator of  claim 1 , wherein the substantially entangled plurality of fibers comprise Needle tacked fibers. 
     
     
         5 . The thermal insulator of  claim 1 , wherein the oxidized polyacrylonitrile fibers have a median fiber diameter of from 1 micrometers to 100 micrometers. 
     
     
         6 . The thermal insulator of  claim 5 , wherein the oxidized polyacrylonitrile fibers have a median fiber diameter of from 5 micrometers to 20 micrometers and a median fiber length of from 25 millimeters to 75 millimeters. 
     
     
         7 . The thermal insulator of  claim 1 , wherein the non-woven fibrous web recovers to at least 70% of its original thickness 5 minutes after being compressed to 37% of its original thickness at ambient conditions. 
     
     
         8 . A thermally insulated assembly comprising:
 a heat source; and   a thermal insulator of  claim 1  at least partially surrounding the heat source.   
     
     
         9 . A method of making a thermal insulator comprising:
 mixing oxidized polyacrylonitrile fibers having crimped configurations with reinforcing fibers having outer surfaces comprised of a polymer with a melting temperature between 100° C. and 300° C.;   heating the fiber mixture to a temperature sufficient to melt the outer surfaces of the reinforcing fibers to provide a non-woven fibrous web; and   entangling the oxidized polyacrylonitrile fibers and reinforcing fibers with each other along a direction perpendicular to the non-woven fibrous web to provide an average bulk density of from 10 kg/m 3  to 35 kg/m 3  in the non-woven fibrous web.   
     
     
         10 . A method of making a thermal insulator comprising:
 mixing oxidized polyacrylonitrile fibers with reinforcing fibers having outer surfaces comprised of a polymer with a melting temperature between 100° C. and 300° C. to obtain a non-woven fibrous web, wherein the oxidized polyacrylonitrile fibers represent over 85% by volume of fibers present that are not reinforcing fibers;   heating the fiber mixture to a temperature sufficient to melt the outer surfaces of the reinforcing fibers to provide a non-woven fibrous web; and   entangling the oxidized polyacrylonitrile fibers and reinforcing fibers with each other along a direction perpendicular to the non-woven fibrous web to provide an average bulk density of from 10 kg/m 3  to 50 kg/m 3  in the non-woven fibrous web.   
     
     
         11 . The method of  claim 9 , further comprising smoothing a major surface of the non-woven fibrous web by calendaring the non-woven fibrous web, heating the non-woven fibrous web, and/or applying tension to the non-woven fibrous web. 
     
     
         12 . The method of  claim 11 , wherein the non-woven fibrous web further comprises a density gradient at the smoothed surface. 
     
     
         13 . The method of  claim 9 , further comprising coating the non-woven fibrous web with a coating fluid selected from the group consisting of silicones, acrylates, and fluoropolymers whereby the non-woven fibrous web has an emissivity of less than 0.5. 
     
     
         14 . A thermal insulator made by the method of  claim 9 . 
     
     
         15 . A method of insulating an electric vehicle battery comprising:
 providing an enclosure adjacent to the electric vehicle battery;   placing the thermal insulator of  claim 1  in compression within the enclosure; and   allowing the thermal insulator to expand and substantially fill the enclosure.