Study on Parameters Affecting the Morphology Development of Dynamically Vulcanized Thermoplastic Elastomers Based on EPDM/PP in a Co-Rotating Twin Screw Extruder

The morphology development of dynamically vulcanized thermoplastic elastomers (TPVs) based on EPDM/PP in a modular intermeshing co-rotating twin screw extruder was studied. Effects of the blend composition and screw speed were considered. The morphological studies were carried out on the cryogenically fractured surface of the samples using Scanning Electron Microscopy (SEM) technique. The flow behavior and melt viscoelastic properties of the samples were also investigated by using Rheometric Mechanical Spectrometer (RMS). The SEM results from TPV samples produced in the twin screw extruder showed a matrix-disperse type morphology similar to those reported for the TPV samples prepared in an internal mixer. The dynamic vulcanization process imposed on the molten blends resulted in a remarkable increase in the steady state torque of the extruder whose extent was found to be dependent upon the EPDM content and screw speed. These results were explained in terms of an agglomerate structure formed between the cured rubber particles. The TPV samples, in particular the samples containing 60% of EPDM, showed a pronounced viscosity upturn and strong elastic modulus (G′) at low frequency range. It was demonstrated that these results in conjunction with the results of relaxation time distribution H(λ) of the samples can provide a great insight into understanding the role of the blend composition and the processing variables on morphology development in the TPV samples in the co-rotating twin screw extruder.