Rheological Behavior of Blends of Metallocene Catalyzed Long-Chain Branched Polyethylenes. Part I: Shear Rheological and Thermorheological Behavior.

Chuangbi Chen,Florian J Stadler,Shuming Cui,Mehdihasan I Shekh

doi:10.3390/polym13030328

Abstract

Long-chain branched metallocene-catalyzed high-density polyethylenes (LCB-mHDPE) were solution blended to obtain blends with varying degrees of branching. A high molecular LCB-mHDPE was mixed with low molecular LCB-mHDPE at varying concentrations. The rheological behavior of those low molecular LCB-mHDPE is similar but their molar mass and molar mass distribution are significantly different. Those blends were characterized rheologically to study the effects of concentration, molar mass distribution, and long-chain branching level of the low molecular LCB-mHDPE. Owing to the ultra-long relaxation times of the high molecular LCB-mHDPE, the blends exhibited a clearly more long-chain branched behavior than the base materials. The thermorheological complexity analysis showed an apparent increase in the activation energies Ea determined from G′, G″, and especially δ. Ea(δ), which for LCB-mHDPE is a peak function, turned out to produce even more pronounced peaks than observed for LCB-mPE with narrow molar mass distribution and also LCB-mPE with broader molar mass distribution. Thus, it is possible to estimate the molar mass distribution from the details of the thermorheological complexity.

Highlights

Polyolefins account for ca. 50% of the synthetic polymers produced worldwide, mainly used for packaging, cable insulation, and household goods
The strain hardening for classical long-chain branched polyethylene, the well-known low-density polyethylene (LDPE), is established to be very good, while for the ZieglerNatta polyethylene (linear low density (ZN-LLDPE) or high density (ZN-HDPE)) usually no strain hardening, at least at high Hencky strain rates [3] . is found [1,2,4,5]
The relatively narrow molar mass distribution of HDPE A combined with the low Mw = 87,000 g/mol leads to an upturn of δ in the δ(|G*|)-plot at relatively high |G*|, which is typical for relatively low molecular LCB-mPE [52]

Summary

Introduction

Polyolefins account for ca. 50% of the synthetic polymers produced worldwide, mainly used for packaging, cable insulation, and household goods. As LCB-mPE has typically about factor 5–10 less long-chain branches than LDPE, their strain hardening level is not as high. Research has shown that shifting G , G” and phase angle δ can provide insight into different aspects of the thermorheological complexity of branched LCB-mPE [22,42] At this point, the determination still suffered from the fact that the determination of the shift factors as a function of the rheological quantity (e.g., G , δ) still had to be done manually. Bai et al [44] and Shen et al [45] blended low and high molecular PE with Mw-ratios around 2.5 and 10 and performed a basic rheological characterization, respectively They found a power-law mixing law; based on their data, their materials are linear.

Rheology

Results

Blends

Conclusions