Dynamically crosslinked thermoplastic elastomer (D-TPE) based on polypropylene (PP)/ethylene-propylene-diene copolymer rubber (EPDM) blends dispersed with surface-coated multiwalled carbon nanotubes (MWCNTs) were prepared as highly-reinforcing nanofillers. Two types of surface-coated MWCNTs, that is, a liquid paraffin (Par) -coated one for affinity with the EPDM phase, and an alpha-olefin (Ole) -coated one for affinity with the PP phase, were used for controlling the dispersion of MWCNTs in the D-TPE. In evaluating the degree of impact of the type and content of the surface-coated MWCNT on the true stress-stretch ratio curve in tensile testing of the MWCNT-dispersed D-TPE, the best fracture characteristic value (tensile true stress and tensile fracture stretch ratio) were obtained when Par-coated MWCNT of 1 vol% was added for the purpose of reinforcing crosslinked EPDM phase., Thus, in Par-coated MWCNT we have elucidated that the enhanced tensile properties of the MWCNT dispersed olefin-based D-TPEs are closely associated with the morphology of the Par-coated MWCNT dispersed D-TPE selectively localized in the crosslinked EPDM phase, showing that the state of MWCNT dispersion is closely linked to improvement of the fracture characteristic value in the true stress-stretch ratio curve.

To predict the fatigue life of CFRTP with high accuracy, it is necessary to ascertain the fatigue failure mechanism of the base material, that is, thermoplastic resin. The failure behavior of thermoplastic resin is greatly affected by polymer orientation, which distributes at random owing to manufacturing process with heating. In this study, the polymer orientation of specimens was identified by THz transmission measurement for the investigation of the correlation between its randomness and fatigue failure mode. As a result, the specimens with small randomness in polymer orientation along the loading axis did not yield fatigue fracture, and significant elongation was observed. The specimens with large randomness yielded fatigue fracture without significant elongation. In the latter case, the local plastic strain range caused by cyclic loading seems higher at the position where the polymer orientation is perpendicular to the loading axis. Fatigue damage seems to accumulate at the perpendicular orientation position so as to yield fatigue fracture. Based on the tentative theory, we conclude that the plastic strain range in the perpendicular direction to fiber orientation seems to align with the polymer orientation and governs the fatigue life of carbon fiber reinforced thermoplastic specimen.