Polyester-based thermoplastic elastomer/MWNT composites: Rheological, thermal, and electrical properties

Polyester-based thermoplastic elastomer (Hytrel®) was melt-compounded with multi-walled nanotubes (MWNTs) using an internal mixer and the changes in the thermal, electrical and rheological properties were investigated using a range of nanotube contents (from 0.1 to 7 wt%). Even at nanotube concentrations as low as 0.1 wt%, the crystallization temperature was remarkably elevated by 15 °C and it increased further up to 22 °C with a 5 wt% loading. On the contrary, the melting temperature increased by 2 °C with 0.1 wt% MWNTs and it was slightly decreased by further additions of MWNTs. Electrical conductivity measured by the four probe method was detected from the 1 wt% MWNTs, indicative of electrical percolation. In addition, MWNTs starting from 4 wt% and above had no significant effect on the electrical conductivity, while it rapidly increased with nanotube contents below 4 wt%. Dynamic rheological properties were measured using a strain controlled rotational rheometer. The complex viscosity increased with MWNT contents giving an abrupt increase between 0.5 and 1 wt% loadings. In addition, the storage and loss modulus increased in a different manner depending on the range of the nanotube concentration. In the Cole-Cole plot, the slope of the nanocomposites decreased from 1.63 to 0.74 with increasing nanotube contents. In the Casson plot, the addition of MWNTs up to 0.5 wt% did not show any yield behavior giving an extremely low value for the yield stress, but further additions of nanotubes increased it notably. The presence of nanotubes in the elastomer increased the relaxation time with nanotube contents and their effect became weak as the frequency increased.