Relationship between the rheology and morphology of dynamically vulcanized thermoplastic elastomers based on EPDM/PP

Relationship between the rheological properties and morphology of dynamically vulcanized thermoplastic elastomers (TPVs) based on Ethylene Propylene Diene Monomer (EPDM) and Polypropylene (PP) blends containing 20,40 and 60% of EPDM were studied. The samples were prepared in a laboratory internal mixer at a rotor speed of 60 rpm. We performed morphological studies on the cryogenically fractured samples using scanning electron microscopy (SEM). The rheological behavior and melt viscoelastic properties of the samples were studied by rheometric mechanical spectrometry (RMS) at a temperature of 220degreesC. The TPV samples showed a significant viscosity upturn and a strong storage modulus that tended to plateau at low shear rates, with the highest extent for the sample containing 60% of EPDM. These results were attributed to a network structure resulting from agglomerates formed between the cured rubber particles, as evidenced by the morphological features of the samples. The multiple elastic response, expressed in terms of relaxation time distribution, H(lambda), exhibited by the molten TPV sample containing 60% of EPDM suggests that apart from the contribution of flow-induced molecular orientation of the PP matrix, there may also exist some elastic response induced by agglomerates formed between the cured rubber particles. The results predicted from the linear viscoelastic model proposed in the present work were found to be in good agreement with the experimental results. (C) 2004 Society of Plastics Engineers.