Melt spinning of metallocene catalyzed polypropylenes. I. On‐line measurements and their interpretation

Abstract

ABSTRACT:The melt spinning of metallocene catalyzed isotactic polypropylene resins was investigated. The details are presented for on-line studies performed on six miPP resins with melt flow rates (MFRs) between 10 and 100 and a Ziegler-Natta catalyzed isotactic polypropylene resin with a MFR of 35 for comparison. The on-line studies indicated that, as the molecular weight and polydispersity increased, crystallization occurred closer to the spinneret at higher crystallization temperatures and under lower spin line stresses. Further, as the spinning speed increased, crystallization occurred closer to the spinneret at higher crystallization temperatures because of increased stress in the spin line. These observations were interpreted in terms of an increased rate of crystallization caused by increased molecular orientation in the spin line with increasing molecular weight and increasing spinning speed. This "stress-enhanced" crystallization was further interpreted in terms of an increased rate of crystal nucleation. It was further concluded that the narrower molecular weight distribution of metallocene resins was the primary factor that produced differences in the structure and properties of fibers spun from these resins compared to those of Ziegler-Natta catalyzed resins of similar weight-average molecular weight or MFR.

Polymorphism in polypropylene fibers

“…The great interest in polypropylene fibers attracted a significant number of investigations into the fiber's structure. [1][2][3][4][5][6][7][8][9] These investigations showed that the structure of as-spun polypropylene fibers is strongly influenced by processing conditions. A change in the formation conditions causes a change in the cooling rate of the extruded filament and a change in the molecular orientation inside the cooled stream, parameters influenced the crystallization process, leading to the formation of the fiber structure.…”

Tensile properties of polypropylene fibres

“…Two processes can be distinguished, depending on the crystallization rate: short spinning (fast crystallization) and long spinning (relatively slow crystallization). At the end of the 20th century, metallocene catalysis allowed the polymer polydispersity to be controlled during its synthesis, leading to an increase in spinning rates and in fibre toughness [49,50]. In short spinning, drawing is mostly performed in the solid state.…”

Structure and Properties of a Metallocene Polypropylene Resin with Low Melting Temperature for Melt Spinning Fiber Application

“…The melt-spinning of metallocene catalyst iPP has been investigated in the last period, Bond and Spruiell demonstrated that the molecular weight and molecular weight distribution (MWD) of metallocene iPP resins had a significant influence on the development of the structure and properties of fibers prepared from these resins. Compared to the Ziegler–Natta-catalyzed resins with similar average molecular weight, the narrower MWD of metallocene resins appeared to be the primary factor that produced differences in the structure and properties of fibers spun from these resins [21]. In addition, the effect of the spinning speed on the density of fibers, crystallinity, and crystalline and non-crystalline orientation function was investigated.…”