Bicomponent fibers with improved curvature

Abstract

Provided are bicomponent fibers with improved curvature. The bicomponent fiber comprises a first region and a second region. The first region comprises a first polyethylene composition and second region comprises a second polyethylene composition, wherein the first polyethylene composition has a crystallization temperature (Tc) greater than a crystallization temperature (Tc) of the second polyethylene composition. The bicomponent fiber can be used to form a nonwoven.

1 . A bicomponent fiber comprising:
 a fiber centroid;   a first region having a first centroid and a second region having a second centroid;   the first region comprising a first polyethylene composition having a molecular weight distribution, expressed as the ratio of the weight average molecular weight to number average molecular weight (M w(GPC) /M n(GPC) ), of less than 3.0;   the second region comprising a second polyethylene composition having a density less than a density of the first polyethylene composition;   wherein at least one of the first centroid and the second centroid is not the same as the fiber centroid; and   wherein the first polyethylene composition has a crystallization temperature (Tc) at least 2° C. greater than a crystallization temperature (Tc) of the second polyethylene composition.   
     
     
         2 . The bicomponent fiber of  claim 1 , wherein the first polyethylene composition has a melting temperature (Tm) at least 2° C. greater than a melting temperature (Tm) of the second polyethylene composition. 
     
     
         3 . The bicomponent fiber of  claim 1 , wherein the melting temperature (Tm) of the first polyethylene composition is less than 130° C. 
     
     
         4 . A bicomponent fiber comprising:
 a fiber centroid;   a first region having a first centroid and a second region having a second centroid;   the first region comprising a first polyethylene composition having a molecular weight distribution, expressed as the ratio of the weight average molecular weight to number average molecular weight (M w(GPC) /M n(GPC) ), of greater than 3.0;   the second region comprising a second polyethylene composition having a density less than a density of the first polyethylene composition;   wherein at least one of the first centroid and the second centroid is not the same as the fiber centroid;   wherein the first polyethylene composition has a crystallization temperature (Tc) at least 3.5° C. greater than a crystallization temperature (Tc) of the second polyethylene composition.   
     
     
         5 . The bicomponent fiber of  claim 4 , wherein the first polyethylene composition has a melting temperature (Tm) at least 5° C. greater than a melting temperature (Tm) of the second polyethylene composition. 
     
     
         6 . The bicomponent fiber of  claim 1 , wherein the density of the first polyethylene composition is at least 0.015 g/cm 3  greater than the density of the second polyethylene composition. 
     
     
         7 . The bicomponent fiber of  claim 1 , wherein the fiber has a curvature of greater than 0.5 mm −1 . 
     
     
         8 . The bicomponent fiber of  claim 1 , where the first polyethylene composition has a Raman measured % crystallinity at least 5.00% greater than a Raman measured % crystallinity of the second polyethylene composition. 
     
     
         9 . A spunbond nonwoven comprising the bicomponent fiber of  claim 1 .