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

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 E-a determined from G ', G '', and especially delta. E-a(delta), 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.

Automated summary

Blends of long-chain branched metallocene-catalyzed high-density polyethylenes (LCB-mHDPE) with varying concentrations of high and low molecular LCB-mHDPE were studied for their rheological behavior, revealing differences in molar mass and distribution. The high molecular LCB-mHDPE in the blends exhibited more pronounced long-chain branching behavior compared to the base materials, with thermorheological analysis indicating increased activation energies corresponding to peak functions. This suggests that details of thermorheological complexity can be used to estimate molar mass distribution in polyethylenes.