Effects of composition and processing conditions on morphology and properties of thermoplastic elastomer blends of SEBS-PP-Oil and dynamically vulcanized EPDM-PP-Oil

This work presents a comparative study of the morphology and structure-related properties of thermoplastic elastomer blends based on SEBS-PP-oil and dynamically vulcanized EPDM-PP-oil prepared under identical conditions. Compositions of each blend type with three different SEBS-PP and EPDM-PP ratios by weight were made in a co-rotating twin-screw extruder and a Brabender internal mixer. A comparative study of different electron microscopic techniques for studying the morphology of these oil-extended blends is reported. Morphological characterization using different microscopic techniques showed a co-continuous morphology for the SEBS-PP-oil blends and droplet-matrix morphology for the thermoplastic vulcanizate (TPV) blends. The particle size distribution of the EPDM-phases in the TPVs prepared in the twin-screw extruder was wider than for the Brabender mixer. No difference in the morphology was observed for the SEBS-PP-oil blends prepared in the twin-screw extruder and Brabender, except for the blend with the highest PP content. The elongation-at-break values were significantly higher for the SEBS-PP-oil blends as compared to the TPV blends. The gel content of the TPVs was the main factor determining the stress-strain properties, as influenced by the preparation method. Also the crystallinity of the PP-phase for both SEBS-PP-oil and TPV blends was investigated and, although being dependent on the preparation method for the SEBS-PP-oil blends, did not reflect in the stress-strain properties.