Rheological properties of ground rubber tire filled isotactic polypropylenes of different molecular weight characteristics

Dynamic rheological properties of the thermoplastic composites containing ground rubber tire have been investigated. Isotactic polypropylenes of different molecular weights were used as thermoplastic polymer matrices. Ground rubber tire powder with a particle size of d = 0.1−0.4 mm was incorporated into the polypropylene by melt blending. The dynamic viscoelastic properties, such as storage and loss moduli, complex viscosity, and loss tangent of polypropylene/ground rubber tire composites were determined in function of ground rubber tire loading and compared with those of the parent polypropylene. The rheological properties of the composites showed shear thinning and power-law behavior. A significant improvement in the melt flowability of polypropylene/ground rubber tire composites was found to depend on the polypropylene molecular weight and the content of ground rubber tire. The higher was the ground rubber tire loading in the composites, the greater was the deviation from the Newtonian flow behavior. Results showed that the viscosity of polypropylene of high molecular weight significantly decreased with the addition of ground rubber tire up to 10 wt.%. The appearance of a minimum in the viscosity curve was traced to the formation of additional free volume in the polymer layers adjacent to the ground rubber tire particles. The dynamic rheological behavior of composites depended strongly on the degree of agglomeration of the ground rubber tire powder.