Abstract
The miscibility of linear polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) blends was studied in relation to the rheological behavior in shearing and elongational deformations of the blends. The rheological properties of four commercial L-PPs with different molecular weights were studied by adding 10, 25, 50, and 75 wt% of LCB-PP to L-PP. The linear viscoelastic properties such as complex viscosity and weighted relaxation spectrum were determined as functions of LCB-PP content. According to the obtained rheological data, the LCB-PP showed a higher zero-shear viscosity and a longer relaxation time than the L-PPs. The linear viscoelastic properties showed an increase in the molecular weight and branched content of the L-PP with a reduction in miscibility. Furthermore, good predictions of linear viscoelastic properties for miscible and immiscible blends were achieved by applying the Palierne model. In uniaxial elongational tests, the L-PP showed no strain hardening behavior. By contrast, the addition of 10 wt% LCB-PP to L-PP resulted in strain hardening behavior at all strain rates. Hence, the strain hardening behavior of the blends was enhanced with LCB-PP content. The elongational viscosity data of the L-PP and LCB-PP and their blends were studied by employing the Molecular Stress Function (MSF) model which could predict the strain hardening behavior of the blends.
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