Rheological behavior of blends from a linear and a long-chain branched polypropylene

This paper investigates how the rheological behavior of a linear polypropylene is changed by blending with different amounts of a long-chain branched polypropylene. The zero shear-rate viscosities of the blends follows the logarithmic mixing rule between the two blend partners up to 50 wt % of the long-chain branched polypropylene. For the blend with 75 wt % long-chain branched polypropylene a deviation from the logarithmic mixing rule was found, which can be referred to a disentanglement of the long-chain branched fraction of molecules during the blend extrusion process similar to the findings for the extruded long-chain branched polypropylene. It is concluded that the linear polypropylene in the blends reduces the extrusion effect on the long-chain branched species in a way that for the blends with up to 50 wt % of the linear PP and no influence of the blend preparation process on the rheological behavior occurred. As the branching structure within the blends remains unchanged it could be shown that the dependence of the zero shear-rate viscosity on the mass average molar mass can be used to characterize the branching architecture of blend components. In uniaxial elongation a pronounced strain hardening was already found for blends with less than 10 wt % long-chain branched polypropylene. The dependency of the strain hardening on the strain rate changes with the amount of the branched polypropylene. (C) 2005 The Society of Rheology.