Carbon nanofiller networks- a comparative study of networks formed by branched versus linear carbon nanotubes in thermoplastic polyurethane

Nanocomposite mechanical properties strongly correlate with filler network strength and quality as affected by filler geometry, size and dispersion quality. However, defining the network quality remains challenging due to the difficulty of assessing nanofiller dispersion, the geometrical complexity of the 3D filler network as well as the unfeasibility of network direct observation. In this study, we compare two nanocomposite systems, one reinforced with carbon nanotubes (CNT) and the other with branched carbon nanotubes or carbon nanostructures (CNS). Thermoplastic polyurethane (TPU) nanocomposites were prepared via in-situ polymerization with the nanofillers dispersed in the polyol prior to the polymerization reaction. Microscopic observations and rheological characterization of polyol suspensions were used to assess filler network quality. This study demonstrates that branched CNTs form stronger networks by comparison with the linear CNTs, which translates into better mechanical performance of the corresponding nanocomposites. In addition, the presence of branches enables the rheological percolation threshold at much lower nanofiller content for the CNS systems by comparison with the CNT ones.