The effect of catalyst addition on the structure, electrical and mechanical properties of the cross-linked polyurethane/carbon nanotube composites

Uniform distribution of filler particles in a polymer matrix is crucial to the improvement of properties of polymer composites. In this work, we have shown that control of the polymerization rate by addition of the catalyst (Fe(acac)3) hinders filler aggregation and enhances electrical and mechanical properties of polyurethane/nanotube composites. Thus, a percolation threshold value of 0.02 wt % obtained for the composites with the catalyst was much lower than the value of 0.65 wt % for the composites without the catalyst. Moreover, the electrical conductivity of the catalytically prepared composites at a nanotube content of 3 wt % was two orders of magnitude higher than that of the non-catalytically prepared ones. The tensile strength of both types of composites showed an improvement at lower filler concentrations, however, the increase of filler content led to deterioration of the mechanical properties for the non-catalytically prepared composites. Structure of the composites was investigated by means of optical and scanning electron microscopy. Additionally, the current-voltage characteristics (J-E) of the composites were studied.