ABSTRACT:The morphology and dynamic viscoelastic properties of isotactic polypropylene (PP) blended with oil-free/oil-extended ethylene-propylene-diene (EPDM) rubbers were studied. Unvulcanized and dynamically vulcanized blends with the compositions PP/EPDM 5 50/50 and 5 30/70 were investigated. The morphology was observed by phase contrasted atomic force microscopy. The dynamic viscoelastic properties were determined with a rheometer of plate-plate configuration. It was shown that the rheological behavior was strongly affected by both the composition and the morphology of the blends. Significant improvement in the flowability of the dynamically vulcanized blends was observed when oil-extended EPDM was used instead of the oil-free version. It was demonstrated that the rheological properties are mostly controlled by the elastomer phase at low frequencies, while in the high-frequency range the influence of PP becomes dominant. The peculiarities in the rheological behavior of the thermoplastic elastomers (uncured blends, TPE) and thermoplastic dynamic vulcanizates (TPV, dynamically cured blends) containing oil-extended EPDMs were traced to a limited compatibility between the PP and EPDM components in the melt.
SYNOPSISFibers of isotactic polypropylene were obtained by high-temperature drawing, adopting a two-stage process. Very high drawing degrees were achieved, more than 40. The physical behavior was analyzed by determining the dynamic-mechanical relaxation spectra in monoaxial stretching. The results obtained show that the elastic modulus reaches a saturation value a t deformation degrees of about 20, well below the drawability upper limit, indicating that above 20 any further drawing does not affect the structure. Moreover the 0 transition appears weak or absent in the drawn samples, while the 01 transition is still readily detectable. Both effects agree with Peterlin's model of drawing and with the fiber structure.
SynopsisPrimary molecular products of mechanical fracture were determined for polymers of different structure. For the first time the velocities of the products translation were measured, and kinetic energies and translation temperatures (2000-5400 K) were calculated.
Thermoplastic vulcanizates (TPVs) based on isotactic polypropylene (iPP) and oil-free/ oil-extended ethylene propylene diene monomer (EPDM) rubber were prepared by dynamic vulcanization. Their rheological and tensile properties as well as morphological peculiarities were examined and compared with those of uncured blends. Vulcanization was performed using two types of cross-linking agents: phenolic resin and sulfuraccelerating systems. Dynamic vulcanization was shown to change the melt viscosity of oil-free and oil-extended iPP/EPDM blends. These changes were found to depend on both rubber content and type of vulcanizing agent. For identical composition, the melt viscosity of TPVs cured by sulfur system was higher than that of blends cured by phenolic resin system (PRS). Dynamic vulcanization by PRS decreased tensile properties of TPVs in comparison with sulfur vulcanization. Morphology of iPP/EPDM blends studied by atomic force microscope was found to be dependent on the ratio of components, type of elastomer, and nature of vulcanizing system.
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