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

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. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3223–3236, 2001

Formation of polypropylene/stearic acid fibers

“…Many studies revealed that the content of mesophase in the fibers depends strongly on the molecular structure of polypropylene and formation parameters 17–20. The high content of mesophase was observed in fibers extruded from polypropylene with low molecular weight,21 fibers taken at low velocities,22–24 or fibers intensively cooled in water with addition of ice or in the mixture of dry ice and acetone 25–29…”

Melt spinning of metallocene catalyzed polypropylenes. II. As‐spun filament structure and properties

“…The resin characteristics for the present set of iPP resins, which included the molecular weight, molecular weight distribution (MWD), and stereoregularity, were described earlier 7. The basic thermal behavior of the resins, including the melting and crystallization temperatures and heat of fusion, is important information that was also presented in part I 7…”

“…The present series of two articles describes the structure and properties of as‐spun filaments produced from a series of metallocene catalyzed iPP (miPP) resins. In the first article of this series7 we presented and interpreted on‐line data for the same set of iPP resins studied in the present report. Furthermore, the effect on the development of the fiber structure of the molecular architecture, which includes the molecular weight characteristics, defect content, and defect type, was discussed for these resins in the first part of this series 7.…”

“…In the first article of this series7 we presented and interpreted on‐line data for the same set of iPP resins studied in the present report. Furthermore, the effect on the development of the fiber structure of the molecular architecture, which includes the molecular weight characteristics, defect content, and defect type, was discussed for these resins in the first part of this series 7. In the present article we further examine the structure developed in the as‐spun filaments and the implications of the structure development on the tensile mechanical properties of the as‐spun filaments.…”

Elastic constants of lamellar and interlamellar regions in α and mesomorphic isotactic polypropylene by AFM indentation

“…The monoclinic α polymorph is stable under ambient conditions . iPP crystallizes predominately in the α form during isothermal crystallization and during melt spinning of filaments . The β polymorph is obtained upon crystallization in a temperature gradient from a sheared melt, or in the presence of β nucleating agents such as quinacridone pigment .…”