Rheological properties of blends of linear and long‐chain branched polypropylenes

Blends of a long‐chain branched polypropylene (LCB‐PP) and a linear polypropylene (L‐PP) were prepared using a twin‐screw extruder. Linear viscoelastic properties such as complex viscosity, storage modulus, and weighted relaxation spectrum were determined as functions of LCB‐PP content. Shear data obtained from commercial rheometers as well as from a slit‐die rheometer were used to verify the Cox‐Merz relation for the neat components as well as for a blend. Elongational properties were obtained using a Sentmanat Extensional Rheometer (SER) unit mounted on an Advanced Rheometric Expansion System (ARES) rheometer and the converging die. A significant strain hardening was observed for the neat LCB‐PP as well as for all the blends, but the strain hardening decreased with increasing strain rate. The apparent steady elongational viscosity values evaluated using the converging die were observed to be comparable at high deformation rates to those obtained from the SER unit, but the differences increased as the strain rate decreased. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers