THE PROPERTY-PERFORMANCE DIFFERENCES BETWEEN 2 BLENDED POLYPROPYLENE FIBERS

The purpose of this study was to characterize two polypropylene copoly mer materials which have similar melt viscosities (melt indices) but b ehave very differently both during and after processing into fibers. A lthough the two materials were generated by two different synthetic ro utes, it was felt that the materials should process similarly because of the similar melt viscosities. The first material, a reactor product , processed normally. With the second material, a physical blend, the spinline tended to break at the spinneret, shutting down the fiber spi nning process. These materials are analyzed using optical microscopy ( OM), differential scanning calorimetry (DSC) and thermomechanical anal ysis (TMA), to examine the source of excessive spin breakage. The sour ce of the spinline breakage is found to be ''gels'' or globular masses on the otherwise smooth surface of the physical blend fibers. Several observations of physical characteristics, such as melting behavior an d tensile stiffness, show that the two materials differ in crystalliza tion rates, fraction, and orientation of crystals, and internal stress states. Much of the evidence points to differences in microstructure, molecular weight and molecular weight distribution between the two ma terials as the root cause of the differences in processability and per formance. This conclusion is supported by gel permeation chromatograph y recently performed on the materials.