Phase morphology development and rheological behavior of non-plasticized and plasticized thermoplastic elastomer blends

The phase morphology development and the final rheological properties of an immiscible polymer blend are generally known to be influenced by the intrinsic viscoelastic and interfacial properties of the constituent polymers and the processing parameters. This dissertation mainly intends to cover the relationship between morphology and rheology of uncross-linked and cross-linked immiscible blends based on ethylene-propylene-diene-terpolymer (EPDM) and polypropylene (PP), in the presence and absence of a low molecular weight paraffinic plasticizer.;Additionally, to elucidate the morphology development of uncross-linked and cross-linked EPDM/PP systems, the non-linear viscoelastic behaviour and morphology evolution of the low viscosity ratio EPDM/PP blends were investigated in a homogeneous shear flow field. The non-reactive and reactive precursors were prepared inside an internal mixer and subsequently subjected to single and multiple start-up transient experiments in a rotational rheometer.;In the non-reactive blends the plasticizer promoted swelling and coalescence, enlarging the size of the polymeric domains and decreasing the specific interfacial area (as measured by AFM) throughout the multiple shearing steps. Meanwhile, the coalescence effect appeared to be more pronounced in low EPDM content blends. On the other hand, due to the higher shear stress exerted by the elastomeric component on the PP phase, a stable fibrilar morphology was obtained at high elastomer content for non-plasticized blends. Interestingly, neither interfacial instabilities and breakup, nor shape relaxation towards sphericity was observed in the non-reactive blends, mainly due to the low interfacial tension between EPDM and PP.;In the reactive blends, the insitu cross-linking reaction resulted in less elongated polymeric domains with an irregular interface and larger specific interfacial area as compared to the non-reactive blends. The EPDM phase in the non-plasticized systems with high elastomer content subjected to long shearing times was transformed into coarse cross-linked EPDM domains encapsulated by the thermoplastic phase showing a tendency towards phase inversion. The presence of the plasticizer reduced the initial curing rate of the elastomeric component in the early shearing stage and resulted in large coalesced EPDM domains, with no tendency towards encapsulation or phase inversion.;To study the effect of the plasticizer on the co-continuity development of the uncross-linked blends, TPOs at various compositions were melt blended inside an internal mixer. Based on a solvent extraction method, it was found that the plasticization promoted a more rapid percolation of the elastomeric component on the low EPDM side of the composition diagram, but keeping an identical onset of co-continuity as compared to the non-plasticized counterparts, i.e. at 40 wt% EPDM. The observed rapid percolation in the presence of the plasticizer was attributed to the non-spherical shape of the EPDM domains and, therefore, to the presence of a certain level of connectivity, as observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM).;Generally, the morphology development inside a homogeneous flow field is quite different from the one generated inside a conventional melt mixing equipment, mainly due the presence of complex flow fields in the latter. Therefore, a comparative study on the morphology development of uncross-linked and dynamically cross-linked high viscosity ratio EPDM/PP blends was performed using an internal mixer and co-rotating twin-screw extrusion. As previously reported, the presence of the plasticizer resulted in a swollen and coalesced EPDM phase in uncross-linked blends (TPOs). The processing comparative study showed furthermore that the majority of the plasticizer in the extruded TPOs resided in the EPDM phase, enabling its deformation in the flow direction. On the other hand, despite a similar average apparent shear rate employed in both mixing equipments, the intensive flow field inside the twin screw extruder resulted in a finer morphology in comparison to the internal mixer. For dynamically cross-linked blends (TPVs), the plasticization showed again a similar coarsening effect, resulting into cross-linked EPDM domains interconnected to some extent. (Abstract shortened by UMI.)...