Moisture Sensitive Auxetic Material

Abstract

An auxetic fiber and corresponding material that not only responds to an external force, but also responds to moisture. The auxetic fiber is made in part from a moisture activated shrinking filament. Even if no external force is applied to the fiber, a pseudo tensile force is created by wetting the auxetic fiber.

1 . An auxetic fiber comprising:
 a first component comprising a moisture sensitive shrinkable filament;   a second component comprising an elastomeric material, wherein the first component is wrapped about the second component in a helical configuration, and wherein the first component is selected from the group consisting of: modified cellulose fibers, rayon, cotton, carboxymethylated cotton, methylated cotton, ethylated cotton, hydroxyethylated cotton, sulfated cotton, sulfonated cotton, phosphate cotton, cationic cotton, amphoteric cotton, sodium acrylate-, acrylic acid-, acryInitrile- or acrylamides grafted cellose fiber and crosslinked fibers thereof, modified wool, modified silk, modified synthetic fiber, a saponified acylonitrile series of fiber, vinilon fiber partially esterfied by maleic acid, yarns made from one or more of the foregoing fibers, and combinations thereof.   
     
     
         2 . The auxetic fiber according to  claim 1  wherein the second component is straight when in a dry state. 
     
     
         3 . The auxetic fiber according to  claim 1  wherein the first component has a cross-sectional area that is between 0.001 and 1 times the cross-sectional area of the second component. 
     
     
         4 . The auxetic fiber according to  claim 1  wherein the first component comprises polyvinyl alcohol. 
     
     
         5 . An array of auxetic fibers comprising:
 a first and a second auxetic fiber each comprising a first component, wherein the first component comprises a moisture activated shrinkable filament, and an elastomeric second component, and wherein the first component is wrapped about the second component in a helical configuration, and wherein the second component is selected from the group consisting of: siloxane, silicone rubber, natural rubber, poly(urethane) and its derivatives, natural rubber, polyisoprene, bytyl rubber and its derivatives, polybutadiene, styrene-butadiene rubber, chloroprene rubber, polychloroprene, neoprene, baypren, ethylene propylene rubber, ethylene propylene diene rubber, epichlorohydrin rubber, polyacrylic rubber, fluorosilicone rubber, fluoroelastomers, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene, ethylene-vinyl acetate, nitrile rubber or polyamides, nylon and combinations thereof.   
     
     
         6 . The array of  claim 5  wherein the first and second auxetic fibers are of opposite handedness. 
     
     
         7 . The array of  claim 5  wherein the second component comprises polyvinyl alcohol. 
     
     
         8 . The array of  claim 5  wherein the second component is straight when in a dry state. 
     
     
         9 . The array of  claim 5  wherein the first auxetic fiber and the second auxetic fiber have first component helices that are in phase. 
     
     
         10 . The array of  claim 5  comprising a woven structure.