Morphology, physical and tensile properties of quench-cooled isotactic polypropylene films and spunbonded fabrics

The room temperature morphology of quench-cooled isotactic polypropylene (iPP) films and its development were investigated by scanning transmittance electron microscopy (STEM) and differential scanning calorimetry (DSC). STEM dark field images revealed that within an amorphous matrix there exist microcrystalline regions, 160 A in size on the average, having the ;Cross polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to monitor morphological changes in the purely crystalline phase of quench-cooled iPP films and spunbonded fabrics during annealing. The spectra were obtained using a pulse sequence that incorporates a delay period with a reduced spin locking field prior to cross polarization. Morphological changes occurring within the purely crystalline phase of iPP were related to observations made by DSC. Upon annealing, the CP/MAS NMR spectrum of the purely crystalline phase of both iPP samples changed by a redistribution in the intensity of the various peaks within a given carbon resonance. This redistribution of intensity was found to reflect the conversion from the ;The tensile properties of the spunbonded iPP fabrics and fibers were enhanced by the dispersion of a silica/silicone additive and by changing the resin characteristics. This additive acts as a nucleating agent for iPP under isothermal crystallization conditions. This nucleating ability manifests itself in smaller crystal sizes and higher nucleation densities in the iPP fibers and bond points. The improved tensile properties are attributed to the smaller crystal sizes which form a more homogeneously dispersed crystalline phase in the amorphous phase as well as to increase the number of load-bearing tie molecules.