Thermoplastic elastomer nanocomposites based on polypropylene and ethylene propylene diene terpolymer (PP/EPDM)

In this study, dynamically vulcanized nanocomposite thermoplastic elastomers (TPV nanocomposites) were prepared by a three-step melt mixing process. Uncured nanocomposite thermoplastic elastomers (TPE nanocomposites) were also prepared using a one-step melt mixing method. Three types of polypropylene (PP) with different melt flow index, an ethylene propylene diene monomer (EPDM), a maleic anhydride modified polypropylene (PPMA) as compatibilizer, and an organo-clay (Cloisite 15A) were employed in this work.; In the first part of this study, we prepared the dynamically-vulcanized nanocomposite thermoplastic elastomers (TPV nanocomposites) based on PP/EPDM (40/60, w/w) while investigating the effect of viscosity ratio of the plastic to the rubber and organo-clay content on their microstructure and mechanical properties. The evolution of the nanocomposite microstructure during the mixing process was also monitored.; The TPV nanocomposites exhibited higher steady-state value of the mixing torque in comparison with similar but unfilled TPVs prepared with PPMA. The XRD results revealed that the peak d001 of the clay in the TPV nanocomposites prepared with activators, accelerators, and sulfur was shifted toward lower angles compared with the original clay (Cloisite 15A). The first characteristic peak of the organo-clay disappeared for the TPV nanocomposites containing different viscosities of PP and 60% EPDM when post processing was applied to these samples. It was found that the microstructure of the prepared TPV nanocomposites is sensitive to the viscosity difference between the two phases (PP, and EPDM) and the clay content. The TEM image of the TPV nanocomposite prepared from low viscosity polypropylene (LVP) before curing stage (selectively reinforced PP-phase TPE nanocomposite) indicated that the silicate layers were dispersed throughout the PP matrix and could not penetrate into the EPDM phase during the mixing process. In the uncured TPV nanocomposites (before curing stage) based on high viscosity PP (HVP), however, the nanoclays were found to be dispersed in the continuous phase (PP) and partly agglomerated at interfacial boundary between the plastic and rubber phases. The TEM image of the TPV sample prepared from 60% EPDM, and 40% LVP at 2 wt% of the organo-clay showed that the silicate layers were nearly exfoliated and randomly distributed into the polypropylene phase. The SEM photomicrographs of the TPV samples prepared with 60 wt% of the elastomer revealed that the rubber particles were dispersed through the polypropylene matrix in form of aggregates and their size increased with the introduction of the clay. The nanoscale dimensions of the dispersed clay resulted in a significant improvement of the tensile modulus of the TPV nanocomposite from 20 to 90% depending on the viscosity ratio of PP/EPDM and the clay content. Moreover, the oxygen permeability in the TPV nanocomposites based on PP/EPDM (40/60) at 2 wt% of the clay was found to be lower than in the unfilled but otherwise similar materials.; The second part of this work is devoted to study the rheological and morphological properties of the dynamically vulcanized nanocomposite thermoplastic elastomers (TPV nanocomposites), based on EPDM and PP containing 20, 40, and 60 wt% of the rubber at 2 wt% of the clay. The effects of composition, PPMA as compatibilizer, and different viscosities of polypropylene were also investigated.; The interlayer distance of the clay was increased in the TPV nanocomposites prepared from different viscosities of PP, but without PPMA, and containing 20, 40 or 60% EPDM. In the TPV nanocomposite (without PPMA) the storage modulus curve significantly increased in comparison with the corresponding matrix. The agglomeration of the clay considerably decreased when the rubber content was increased. The yield stress of the prepared TPV nanocomposites, based on low viscosity PP, increased more than that for the hybrids having high viscosity PP. Th...