Bicomponent Polymeric Fibers

Abstract

A bicomponent fiber comprising a sheath, where the sheath includes a propylene-based elastomer, said propylene-based elastomer including propylene-derived units and from about 3.0 to about 15 wt % alpha-olefin-derived units other than propylene-derived units, based upon the entire weight of the copolymer, said propylene-based elastomer having a triad tacticity of greater than 75%, and a heat of fusion, as determined by DSC, of less than 75 J/g; and a core, where the melt temperature of the core, as determined by DSC, is at least 5% greater than the melt temperature of the sheath.

What is claimed is: 
     
         1 . A bicomponent fiber comprising:
 a sheath, where the sheath includes a propylene-based elastomer, said propylene-based elastomer including propylene-derived units and from about 3.0 to about 15 wt % alpha-olefin-derived units other than propylene-derived units, based upon the entire weight of the copolymer, said propylene-based elastomer having a triad tacticity of greater than 75%, and a heat of fusion, as determined by DSC, of less than 75 J/g; and   a core, where the melt temperature of the core, as determined by DSC, is at least 5% greater than the melt temperature of the sheath.   
     
     
         2 . The bicomponent fiber of  claim 1 , where the melt temperature of the core, as determined by DSC, that is greater than 125° C. and the flexural modulus of the core, as determined by ASTM D-790, is greater than 1,000 MPa. 
     
     
         3 . The bicomponent fiber of  claim 1 , where the melt temperature of the core is at least 20% greater than the melt temperature of the sheath. 
     
     
         4 . The bicomponent fiber of  claim 1 , where the melt temperature of the core is at least 15° C. greater than the melt temperature of the sheath. 
     
     
         5 . The bicomponent fiber of  claim 1 , where the melt temperature of the core is at least 30° C. greater than the melt temperature of the sheath. 
     
     
         6 . The bicomponent fiber of  claim 1 , where the flexural modulus of the core is at least 1,000 MPa greater than the flexural modulus of the sheath. 
     
     
         7 . The bicomponent fiber of  claim 1 , where the flexural modulus of the core is at least 1,300 MPa greater than the flexural modulus of the sheath. 
     
     
         8 . The bicomponent fiber of  claim 1 , where the total ethylene-derived units within the sheath is less than 30 wt % based upon the entire weight of the polymeric content of the sheath. 
     
     
         9 . The bicomponent fiber of  claim 1 , where the alpha-olefin-derived units are ethylene-derived units, and where the propylene-based elastomer includes less than 8 wt % ethylene-derived units. 
     
     
         10 . The bicomponent fiber of  claim 9 , where the propylene-based elastomer includes less than 6 wt % ethylene-derived units. 
     
     
         11 . The bicomponent fiber of  claim 1 , where the sheath has a flexural modulus, according to ASTM D-790, of from about 100 to about 1,000 MPa. 
     
     
         12 . The bicomponent fiber of  claim 1 , where the sheath has a melt temperature, as determined by DSC, of from about 85 to about 120° C. 
     
     
         13 . The bicomponent fiber of  claim 1 , where the sheath includes a first propylene-based elastomer and a second propylene-based elastomer, where the first propylene-based elastomer has an MFR, according to ASTM D-1238, 2.16 kg weight @ 230° C., of from about 6 to about 55 g/10 min, and where the second propylene-based elastomer has an MFR, according to ASTM D-1238, 2.16 kg weight @ 230° C., of from about 6 to about 80 g/10 min. 
     
     
         14 . A nonwoven fabric comprising:
 a bicomponent fiber including a core and sheath, where the sheath includes a propylene-based elastomer that includes propylene-derived units and from about 3.0 to about 15 wt % alpha-olefin-derived units, based upon the entire weight of the copolymer, has a triad tacticity of greater than 75%, and a heat of fusion, as determined by DSC, of from about 30 to about 75 J/g.   
     
     
         15 . The nonwoven fabric of  claim 14 , where the alpha-olefin-derived units are ethylene-derived units, and where the propylene-based elastomer includes less than 8 wt % ethylene-derived units. 
     
     
         16 . The nonwoven fabric of  claim 14 , where the melt temperature of the core, as determined by DSC, is at least 5% greater than the melt temperature of the sheath. 
     
     
         17 . The nonwoven fabric of  claim 14 , where the melt temperature of the core, as determined by DSC, is greater than 125° C. and the flexural modulus of the core, as determined by ASTM D-790, is greater than 1,000 MPa. 
     
     
         18 . The nonwoven fabric of  claim 14 , where the sheath has a melt temperature, as determined by DSC, of from about 85 to about 120° C. 
     
     
         19 . A process for forming bicomponent polymer fibers, the process comprising:
 extruding first and second polymeric compositions to thereby form a sheath-core structure, where the first polymeric composition forms the sheath and the second polymeric composition forms the core, where the first polymeric composition includes a propylene-based polymer and from about 3 to about 15 wt % alpha-olefin-derived units, has a triad tacticity greater than about 75%, and a heat of fusion less than about 75 J/g.   
     
     
         20 . The process of  claim 19 , further comprising the step of forming a web of the fibers. 
     
     
         21 . A process for forming an air-through nonwoven fabric, the process comprising:
 i. providing bicomponent fiber including a sheath, where the sheath includes a propylene-based elastomer, said propylene-based elastomer including propylene-derived units and from about 3.0 to about 15 wt % alpha-olefin-derived units other than propylene-derived units, based upon the entire weight of the copolymer, said propylene-based elastomer having a triad tacticity of greater than 75%, and a heat of fusion, as determined by DSC, of less than 75 J/g, and a core, where the melt temperature of the core, as determined by DSC, is at least 5% greater than the melt temperature of the sheath   ii. forming fibers into a web of the fibers; and   iii. exposing the web to air having a temperature from 100 C.° to 120 C.° to thereby bond the fibers within the web.   
     
     
         22 . The process of  claim 21 , wherein a pack pressure less than 600 psi at 0.6 ghm is used to form the fibers.