Effect of residual contaminants and of different types of extrusion processes on the rheological properties of the post-consumer polypropylene

Rheological measurements were conducted to verify the influence of different mechanical recycling processes and the presence of contaminants on the degradation of post-consumer polypropylene. Firstly, polypropylene (PP) was contaminated to simulate a post-consumer material, following the protocol recommended by the FDA. PP was subsequently recovered (washed and dried) and the samples were submitted to different extrusion processes. The rheological data demonstrated that the different types of processing applied and the presence of contaminants altered the molecular structure of the samples. The contaminants acted as agents that accelerated the polymer degradation. The contaminated samples submitted to higher shear rates exhibited greater decrease in their molar mass and a slight narrowing in the molar mass distribution. Also, it was observed that the most degraded samples showed decrease in their molar mass, in the viscosity and in the level of their molecular entanglements. These samples also exhibited a more Newtonian behavior and their molar mass distribution showed a slight narrowing. By calculating the ratio of the molar mass it was possible to quantify the degree of degradation of PP samples, confirming the results obtained.