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

Renwei Xu,Jinpeng Su,Hai Wang,Xu Chen,Zhicheng Zhang,Peng Zhang,Peng Chen,Jie Xiong

doi:10.3390/polym11040729

Abstract

An isotactic polypropylene (iPP-1) resin with low melting temperature (Tm) is synthesized by a metallocene catalyst and investigated for melt-spun fiber applications. The structure, thermal and mechanical properties, and feasibility of producing fibers of a commercial metallocene iPP (iPP-2) and a conventional Ziegler–Natta iPP (iPP-3) are carefully examined for comparison. Tm of iPP-1 is about 10 °C lower than the other two samples, which is well addressed both in the resin and the fiber products. Besides, the newly developed iPP-1 possesses higher isotacticity and crystallinity than the commercial ones, which assures the mechanical properties of the fiber products. Thanks to the addition of calcium stearate, its crystal grain size is smaller than those of the two other commercial iPPs. iPP-1 shows a similar rheological behavior as the commercial ones and good spinnability within a wide range of take-up speeds (1200–2750 m/min). The tensile property of fibers from iPP-1 is better than commercial ones, which can fulfill the application requirement. The formation of the mesomorphic phase in iPP-1 during melt spinning is confirmed by the orientation and crystallization investigation with wide angle X-ray diffraction (WAXD), which is responsible for its excellent processing capability and the mechanical properties of the resultant fibers. The work may provide not only a promising candidate for the high-performance PP fiber but also a deep understanding of the formation mechanism of the mesomorphic phase during fiber spinning.

Highlights

The majority of nonwoven polyolefin fibers are of great commercial interest because of their unique properties, including hydrophobicity, good mechanical properties, and excellent chemical resistance [1,2]
We present a low-melting-temperature metallocene isotactic polypropylene (iPP) for melt spinning fiber application
Isotactic polypropylene sample 1 is synthesized from C2 -symmetric metallocene catalysts (rac-Me2 Si(2-Me-4-Ph-Ind)2 ZrCl2 ) [24] with a molecular weight (Mw) of 147,000 and polymer dispersity index (PDI) of 2.5, which is a pilot product synthesized by the China Petroleum Lanzhou Chemical Research Center (Lanzhou, China)

Summary

Introduction

The majority of nonwoven polyolefin fibers are of great commercial interest because of their unique properties, including hydrophobicity, good mechanical properties, and excellent chemical resistance [1,2]. Traditional commercial iPP is generally polymerized with a heterogeneous titanium-based Ziegler–Natta catalyst, whose tacticity, molecular weight (Mw ), and polymer dispersity index (PDI) are tightly dependent on the catalysts and the polymerization. In comparison with the Ziegler–Natta-catalyzed polypropylene (PP), metallocene polypropylenes are uniform polymers with precisely controlled Mw , end groups, stereoregularity, and narrow PDI [6]. Those characters make metallocene-based iPP a great candidate for producing high-quality industrial fibers by melt spinning

Methods

Results

Conclusion