Suppression in Melt Viscosity of the Homogeneously Mixed Blends of Polypropylene (iPP–UHMWiPP) in the Presence of an Oxalamide

Abstract

Here we report on the influence of an aliphatic oxalamide-based nucleating agent (OXA3,6) on the viscoelastic and mechanical properties of isotactic polypropylene (iPP) blended with ultrahigh molecular weight iPP (UHMWiPP). The linear viscoelastic properties are investigated by using a plate−plate rheometer; the presence of only 0.5 wt % of OXA3,6 in the iPP−UHMWiPP blends results in a reduction of the complex viscosity in the entire frequency domain examined. This observation holds irrespective of the UHMWiPP weight fraction, up to 25 wt %. The viscosity suppression is attributed to an acceleration of the reorientation times of the chains, especially the longer ones, due to partial alignment of their molecular segments. Furthermore, SAXS measurements on cooled, injection molded samples hint that OXA3,6-containing samples display enhanced alignment under processing conditions (injection molding). Compared to samples without OXA, an increase in the SAXS intensity along the equator is observed in the OXA3,6 samples, implying an enhanced ability of shish-kebab formation. Such a morphological development results in higher yield stress while maintaining the elastic behavior.

An Unconventional Route for Synthesis and Solid‐State Processing of Low‐Entangled Ultra‐High Molecular Weight Isotactic Polypropylene

“…An example is provided in the melt blending of the low-and ultra-high molecular weight isotactic polypropylene (UHMWiPP) in the presence of a nucleating agent which allows suppression of the melt viscosity, leading to an increase in mechanical properties. [5] However, the normally adopted melt processing route to produce fibers or tapes of UHMW encounters challenges due to the enhanced melt viscosity of such high molar masses. To recall, with the increasing chain length, as a) General conditions: propylene = 1.1 bar (absolute pressure), polymerization temperature = 40 °C, solvent = 750 mL heptane, 0.55 mL tri-iso-butyl aluminum solution in toluene (25 wt%), catalyst and co-catalyst = 10 μmol (Hf/B = 1), total of 9 mL of toluene for catalyst/co-catalyst dissolution; b) Kg i PP /mol cat h bar; c) Determined by melt-shear rheology [9] (left) and HT-GPC (right); d) Determined by high temperature- 13 C nuclear magnetic resonance on the methyl signal (Figure S1, Supporting Information); e) Peak melting temperature determined on the first heating cycle using DSC at 10 °C min −1 .…”

Fiber Spinning of Ultrahigh Molecular Weight Isotactic Polypropylene: Melt Spinning and Melt Drawing

“…Therefore, ultrahigh molecular weight iPP (UHMW‐iPP) fibers potentially could outperform UHMW‐PE Dyneema fibers. However, the processing of UHMW polymer fibers via the classic melt extrusion route is considered very challenging and even a few claim it to be nearly impossible [4] . This is mainly attributed to the high melt viscosity, which correlates with the polymer's molecular weight with η 0 ∝ M w 3.4 [5] .…”

“…[3] Compared to polyethylene (PE), iPP has some serious advantages: an almost 25 °C higher melting transition, a higher tensile strength and impact resistance as well as a lower mass density. [4] Therefore, ultrahigh molecular weight iPP (UHMW-iPP) fibers potentially could outperform UHMW-PE Dyneema fibers. However, the processing of UHMW polymer fibers via the classic melt extrusion route is considered very challenging and even a few claim it to be nearly impossible.…”

“…However, the processing of UHMW polymer fibers via the classic melt extrusion route is considered very challenging and even a few claim it to be nearly impossible. [4] This is mainly attributed to the high melt viscosity, which correlates with the polymer's molecular weight with η 0 ∝ M w 3.4 . [5] To circumvent this, a few attention was directed onto the gel-spinning process for UHMW-iPP fiber production.…”

“…Compared to polyethylene (PE), iPP has some serious advantages: an almost 25 °C higher melting transition, a higher tensile strength and impact resistance as well as a lower mass density [4] . Therefore, ultrahigh molecular weight iPP (UHMW‐iPP) fibers potentially could outperform UHMW‐PE Dyneema fibers.…”