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

• Main Authors: Chuangbi Chen, Mehdihasan I. Shekh, Shuming Cui, Florian J. Stadler
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Polymers
• Subjects: polyethylenes; blends; long-chain branches; thermorheological complexity; activation energy spectrum
• Online Access: https://www.mdpi.com/2073-4360/13/3/328

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 <i>E_a</i> determined from <i>G′</i>, <i>G″</i>, and especially δ. <i>E_a</i>(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.