Understanding the effect of short-chain branches by analyzing viscosity functions of linear and short-chain branched polyethylenes

In this paper, we assess the frequency dependent rheological data of several different linear and short-chain branched metallocene catalyzed polyethylenes with respect to the description of the viscosity functions. The aim is to derive material specific relaxation time λ from the fit. This characteristic relaxation time follows a similar dependence to the molar mass Mw as the zero shear-rate viscosity, but slightly depends on both molar mass distribution and comonomer content. The transition between the shear-thinning region and the terminal regime is broader for mHDPE than for mLLDPE and widens with increasing molar mass Mw. This finding is explained by the differences in the plateau modulus GN0 and the increase of the normalized terminal relaxation time in comparison to the characteristic relaxation time, respectively.