Influence of the molecular structure of polyolefins on the damping function in shear

This paper deals with the nonlinear shear behavior of linear and long-chain branched polyethylenes (PE) and polypropylenes (PP) as determined at high step strains. For linear polyethylenes, the comonomer content, molar mass, and molar mass distribution were confirmed to have no influence on the damping function, while a clear difference between linear PP and PE was obvious. Long-chain branched metallocene catalyzed polyethylene (mPE) as well as irradiated long-chain branched PP samples showed a weaker strain dependence compared to their linear counterparts depending on the amount of branching. With an increasing number of long-chain branches, this trend becomes more pronounced. Most of the damping functions measured can well be described by a function similar to the Carreau - Yasuda equation. The relation of the three parameters of this equation with the molecular structure of the samples is discussed.