Shear Rheology of Blends of a Linear and a Long Chain Branched Polypropylene

Linear and relatively narrow molecular weight distribution of polypropylene produced by Ziegler-Natta catalysts result in low melt strength and weak strain hardening in elongational flows. These properties of a linear polypropylene (L-PP) are effectively enhanced by blending with long-chain branched polypropylene (LCB-PP). This paper investigates how the rheological behavior of a L-PP is changed by blending with different amounts of a LCB-PP. Linear viscoelastic properties of blends such as complex viscosity and storage modulus were determined as functions of LCB-PP content. The LCB-PP exhibits a pronounced shear thinning behavior and higher zero shear viscosity than L-PP. It was shown that increasing of LCB-PP content shifted the transition from Newtonian plateau to the power law region at lower frequencies. The logarithmic mixing rule for complex viscosity in different frequencies is used to investigate the miscibility of blends. Semicircular shape of Cole-Cole plot of different blends is an evidence of miscibility

Keywords:

Long-Chain Branching , Polypropylene , Rheology