Effect of the melt processing conditions on the conductive paths formation in thermoplastic polyurethane/expanded graphite (TPU/EG) composites

With the aim to produce electrically conductive composites, we analysed the influence of the melt processing conditions on the electrical percolation threshold concentration in thermoplastic polyurethane (TPU)/expanded graphite (EG) composites. Melt mixing and compression moulding temperature as well as rotational speed significantly affect the electrical percolation concentration. While at mixing conditions where a homogeneous composite is obtained the percolation concentration is above 4 wt.%, lower percolation concentration of <2 wt.% (corresponds to <1 vol.%) was reached at processing conditions where a certain degree of agglomeration remained. The conductivities determined with two different electrode systems revealed increased resistance in the surface near regions. Overall, the conductivities of the composites are rather small if compared to that of EG. Furthermore, EG nucleates the crystallisation of the hard segments and affects the thermal and mechanical properties of TPU.