BICOMPONENT FIBERS AND METHODS FOR MAKING THEM
The present invention relates to bicomponent polymer fibers, and to processes for forming those fibers. Bicomponent polymer fibers are described, having a core comprising a core polymer and a sheath comprising a sheath polymer, wherein the sheath polymer is a polyolefm having an Mw less than about 65,000 g/mol. The core polymer has an Mw at least about 20,000 g/mol greater than the Mw of the sheath polymer. Processes for forming bicomponent fibers are also described, comprising (i) forming a molten blend of a core polymer and a sheath polymer; (ii) extruding the molten polymer blend using an extrusion die having a length to diameter ratio greater than or equal to about 10 and under shear conditions sufficient to drive the sheath polymer to the die wall; and (iii) forming meltblown fibers having a core comprising the core polymer and a sheath comprising the sheath polymer.