ENHANCEMENT OF TENSILE PROPERTIES OF ISOTACTIC POLYPROPYLENE SPUNBONDED FABRICS BY A SURFACE-MODIFIED SILICA SILICONE COPOLYMER ADDITIVE/

Previous work at Kimberly-Clark Corp. (R. S. Nohr and J. G. MacDonald, Kimberly-Clark Corp., unpublished results, 1990) demonstrated that th e addition of an ultrafine-particle( submicron size), surface-modified silica predispersed in an alkyl silicone to isotactic polypropylene ( iPP) results in dramatic improvements in the tensile properties of fib ers and spunbonded fabrics. For both fibers and spunbonded fabrics pre pared with a high concentration of the low melt flow index (MFI) resin the incorporation of the additive resulted in markedly improved tensi le properties. In this article it is shown that under quiescent condit ions the surface-modified silica/silicone copolymer additive acts as a n effective nucleating agent for IPP. This results in a reduction in t he size of the crystalline entities, hence a more homogeneously distri buted crystalline phase and load-bearing ''tie'' molecules. Indeed, sc anning transmittance electron microscopy (STEM) studies show that the crystalline entities are substantially smaller at the surface and mid- radius of fibers prepared with additive containing iPP. Furthermore, t he bond points of the resulting spunbonded fabrics have a dramatically increased nucleation density and smaller crystallite dimensions. (C) 1997 John Wiley & Sons, Inc.