Effect of Recycling on the Rheological Properties and Foaming Behaviors of Branched Polypropylene

The effects of recycled-branched polypropylenes on their rheological properties and foamability are studied and compared with the virgin sample in this paper. The main idea is 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 disentanglement. However, the viscosity at a high shear rate for virgin and recycled samples remains almost the same whereas the zero-shear rate viscosity was lower for recycled samples. The rheological behavior of the samples 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 materials and the virgin material were studied at various processing temperatures using a single-screw tandem foam extrusion system. The volume expansion ratio, cell population density results were correlated with the rheological data. Despite the noticeable drop in the melt strength, it was found that the foamability was not significantly deterorated by the recycling process.