Bicomponent fibers derived from immiscible polymer blends

Polypropylene fibers are extensively used in nonwovens, but are perceived as having undesirable tactile characteristics (plastic-like). This study investigates the use of immiscible polymer blends as the sheath component in bicomponent fibers with a polypropylene core. The sheath consists of blends of a continuous polyethylene phase (70 vol%) containing polystyrene or polyamide-6 as the dispersed phase (30 vol%). The bicomponent fibers are melt spun over a range of speeds (undrawn to 2000 m/min) and for two sheath contents (12.5 and 20 vol%). The immiscible blends create an irregular fiber surface, with the crystalline nature of the dispersed phase having the greatest effect on the resulting surface characteristics. The polystyrene dispersed phase creates an irregular fiber surface, whereas the polyamide dispersed phase results in a smoother fiber surface. Stresses experienced during fiber spinning lead to the formation of a fibrillar dispersed phase for polyamide-6, whereas the amorphous polymer phase produces an ellipsoidal (i.e., nonfibrillar) dispersed phase. As fiber surface irregularities increase, tensile properties decrease. This study illustrates the range of surface properties that can be generated by using incompatible blends as the sheath material in bicomponent fibers.