Rheology as a powerful help for the characterization of the morphology of thermoplastic elastomers (TPE) based on PP and reclaimed EPDM rubber

The morphology of blends of reclaimed rubber of ethylene, propene and diene monomers (EPDM) with poly (propylene) (PP), elaborated by melt mixing in an internal mixer or by twin screw extrusion, was investigated. A poor dispersion was observed by microscopy in the case of dispersed phase morphology of EPDM in the PP matrix. Because this technique became difficult when the EPDM content increased, dynamic mechanical spectroscopy was used instead and, combined with modeling, was shown to be of powerful help. The model developed by Veenstra for mechanical properties of blends was extended to the case of the dynamic rheology of viscoelastic melts. The analysis and modeling of the frequency dependence of the dynamic moduli enabled to distinguish the various morphologies of PP-reclaimed EPDM blends. In particular, in the medium composition range, reclaimed rubber and PP formed co-continuous phases and the morphology turned to a dispersion of PP in EPDM at high rubber content. The same trend was noted whether the blends were obtained in the mixer or in the extruder.