Effect of recycling on the rheological properties and foaming behaviors of branched polypropylene

The effects of recycling of branched polypropylenes on their rheological properties and foamability are studied in this paper. The rheological properties and foamabilitly of branched polypropylene are compared with those of the virgin sample. The main purpose of the study was to explore the possibility of using recycled materials to make the acceptable foam products. The recycled polypropylenes showed the lower melt strength due to the lowered molecular weight and disentanglement of molecules. However, the high-shear viscosities of the virgin and recycled resins exhibited almost the same values whereas the zero-shear rate viscosity, was lower for recycled ones. The rheological behavior of the resins was correlated to the foaming behavior. It was observed that the contribution of the storage modulus (G') was more pronounced than the loss modulus (G"). The foam morphology of recycled branched polypropylene and the virgin material was studied at various processing temperatures using a single-screw tandem foam extrusion system. The volume expansion ratio and cell population density results were correlated with the rheological data. Despite the noticeable drop in the melt strength, it was found that the foamability did not significantly deteriorate by recycling.