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 M _w 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 M _w. This finding is explained by the differences in the plateau modulus G _N ⁰ and the increase of the normalized terminal relaxation time in comparison to the characteristic relaxation time, respectively.