Melt Spinning of Plastic-Grade Polypropylene

Diana Gregor-Svetec

University of Ljubljana, Faculty of Natural Sciences and Engineering, Snežniška 5, SI-1000, Ljubljana, Slovenia
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The goals of our research were to optimize the melt spinning of filaments spun from plastic-grade polypropylene polymer and to compare the structural characteristics of as-spun filaments obtained from plastic- and fiber-grade polymers. The melt spinning of polypropylene filaments was carried out on an Extrusion Systems Ltd. laboratory spin-draw device. The spinning process was optimized in order to avoid the onset of spinline instabilities and spinline diameter fluctuations and was carried out as gravitational spinning with no-take-up application. From measurement of the average molecular weight and molecular weight distribution, some degradation of molecules and narrowing of molecular weight distribution in both types of as-spun filaments was determined. At both tested as-spun filaments, produced by rapid cooling of an extruded jet, only the spherulitic structure composed of α-monoclinic crystals was established. In comparison to the filaments spun from the fiber-grade polymer, filaments spun from the plastic-grade polymer had higher density, melting enthalpy, and higher crystallinity, resulting in higher tenacity of these filaments.

Keywords: Polypropylene, melt spinning, as-spun filaments, WAXS, SEM, SEC/LALLS