Influence of thermal treatment on the elastic modulus of a nano-dispersed elastomer domain in an injection-molded isotactic polypropylene/thermoplastic elastomer binary blend

Here, the nano-scale elastic modulus of a phase-separated polyolefin blend consisting of isotactic polypropylene (iPP) and ethylene- co -octene rubber (EO) was investigated using atomic force microscopy (AFM). We investigated the elastic modulus of the EO domain for the injection-molded specimens with three different annealing temperatures: without further annealing (“as-is”), 100 °C annealing (“100 °C”), and 155 °C annealing (“155 °C”). The shapes of the EO domains of those specimens were observed as fibrous and highly oriented along the flow direction. However, the elastic moduli of the EO domains were distributed differently depending upon their annealing temperatures. The elastic modulus in the “as-is” sample was distributed from 2 to >50 MPa, with higher modulus EO domains (>10–50 MPa) than the inherent elastic modulus of the EO. These domains were supposed to be derived from the high-stress EO domain based on the negative pressure accumulated inside the fibrous EO domain, which is attributed to the elongated and tense EO molecules. The 100 °C specimen, with an annealing temperature that was much higher than the melting point of the EO, still contained many higher elastic modulus EO domains, demonstrating that the 100 °C annealing temperature was still insufficient to remove the stress inside these EO domains. Finally, the 155 °C sample did not show any higher modulus EO domains, and its elastic modulus distribution became closer to that of the inherent EO. Elastic moduli of nano-dispersed elastomer domains in injection molded isotactic polypropylene (iPP)/ethylene-co-octene elastomer (EO) binary blends were investigated by an atomic force microscopy. The EO domains were highly elongated to the flow direction. The elastic modulus distribution of the EO domains was quite different depending on the annealing conditions.