Modified Polylactic Acid Fibers

Abstract

A multi-component fiber that includes a core component surrounded by a distinct sheath component is provided. The core component is formed primarily from polylactic acid and the sheath component is formed primarily from a polymeric toughening additive.

1 . A method for forming a multi-component fiber, the method comprising blending a polylactic acid, polymeric toughening additive, and polyepoxide modifier to form a thermoplastic composition, and thereafter extruding the thermoplastic composition through a die to form a fiber, wherein the fiber contains a core component surrounded by a sheath component, and wherein the polylactic acid constitutes about 50 wt. % or more of the polymer content of the core component and the polymeric toughening additive constitutes about 50 wt. % or more of the polymer content of the sheath component. 
     
     
         2 . The method of  claim 1 , wherein the polymeric toughening additive constitutes from about 90 wt. % to 100 wt. % of the polymer content of the sheath component. 
     
     
         3 . The method of  claim 1 , wherein the sheath component constitutes from about 0.5% to about 25% of the diameter of the fiber. 
     
     
         4 . The method of  claim 1 , further comprising forming pellets from the blended thermoplastic composition, and extruding the pellets through the die to form the fiber. 
     
     
         5 . The method of  claim 4 , wherein the pellets are formed using an underwater pelletizer. 
     
     
         6 . The method of  claim 1 , wherein the ratio of the melt flow rate of the polylactic acid to the melt flow rate of the polymeric toughening additive is from about 0.1 to about 0.9. 
     
     
         7 . The method of  claim 1 , wherein the polymeric toughening additive is a polyolefin. 
     
     
         8 . The method of  claim 1 , wherein the polyepoxide modifier includes an epoxy-functional (meth)acrylic monomeric component. 
     
     
         9 . The method of  claim 8 , wherein the epoxy-functional (meth)acrylic monomeric component includes glycidyl acrylate, glycidyl methacrylate, or a combination thereof. 
     
     
         10 . The method of  claim 1 , wherein the polyepoxide modifier is poly(ethylene-co-methacrylate-co-glycidyl methacrylate). 
     
     
         11 . The method of  claim 1 , wherein the polylactic acid constitutes about 70 wt. % or more of the thermoplastic composition. 
     
     
         12 . The method of  claim 1 , wherein blending occurs at a temperature above the melting point of the polylactic acid and below a temperature of about 230° C. 
     
     
         13 . The method of  claim 1 , wherein extrusion of the blended thermoplastic composition occurs at a temperature above about 230° C. 
     
     
         14 . The method of  claim 1 , wherein the blended thermoplastic composition comprises a plurality of discrete domains dispersed within a continuous phase, the discrete domains containing the polyepoxide modifier and the continuous phase containing polylactic acid. 
     
     
         15 . The method of  claim 1 , further comprising drawing the extruded thermoplastic composition. 
     
     
         16 . A fiber formed by the method of  claim 1 . 
     
     
         17 . A multi-component fiber that contains a core component surrounded by a sheath component, wherein polylactic acid constitutes about 50 wt. % or more of the polymer content of the core component and a polymeric toughening additive constitutes about 50 wt. % or more of the polymer content of the sheath component, wherein the polylactic acid in the core component and the polymeric toughening additive in the sheath component are derived from a single thermoplastic composition in which the polylactic acid is blended with the polymeric toughening additive. 
     
     
         18 . The multi-component fiber of  claim 17 , wherein the polymeric toughening additive constitutes from about 90 wt. % to 100 wt. % of the polymer content of the sheath component. 
     
     
         19 . The multi-component fiber of  claim 17 , wherein the sheath component constitutes from about 0.5% to about 25% of the diameter of the fiber. 
     
     
         20 . The multi-component fiber of  claim 17 , wherein the ratio of the melt flow rate of the polylactic acid to the melt flow rate of the polymeric toughening additive is from about 0.1 to about 0.9. 
     
     
         21 . The multi-component fiber of  claim 17 , wherein the polymeric toughening additive is a polyolefin. 
     
     
         22 . The multi-component fiber of  claim 17 , wherein the core component further comprises a polyepoxide modifier. 
     
     
         23 . The multi-component fiber of  claim 22 , wherein the polyepoxide modifier includes an epoxy-functional (meth)acrylic monomeric component. 
     
     
         24 . The multi-component fiber of  claim 22 , wherein the polyepoxide modifier is poly(ethylene-co-methacrylate-co-glycidyl methacrylate). 
     
     
         25 . The multi-component fiber of  claim 17 , wherein the fiber exhibits a peak elongation of about 50% or more and a tenacity of from about 0.75 to about 6 grams-force per denier. 
     
     
         26 . A nonwoven web comprising a plurality of multi-component fibers that contain a core component surrounded by a sheath component, wherein polylactic acid constitutes about 50 wt. % or more of the polymer content of the core component and a polymeric toughening additive constitutes about 50 wt. % or more of the polymer content of the sheath component, wherein the polylactic acid in the core component and the polymeric toughening additive in the sheath component are derived from a single thermoplastic composition in which the polylactic acid is blended with the polymeric toughening additive. 
     
     
         27 . An absorbent article comprising an absorbent core positioned between a liquid-permeable layer and a generally liquid-impermeable layer, the absorbent article comprising the nonwoven web of  claim 26 .