Electrical and thermal conductivities of multiwalled carbon nanotubes-reinforced high performance polymer nanocomposites

Polyethersulfone (PES) and phenoxy based-nanocomposites filled with unmodified multi-walled carbon nanotubes (MWCNT) from 0.25 to 10 wt.% have been prepared by melt processing with a twin-screw extruder and a hot press. A morphology analysis is performed by transmission electron microscopy (TEM) in the extruded nanocomposites disclosing difference in state of dispersion despite a proper MWCNT scattering in both matrixes. The electrical conductivity measurements establish a percolation threshold Phi(c) = 0.58 wt.% and a critical exponent t = 2.3 for phenoxy against Phi(c) = 0.89 wt.% and t = 1.89 for PES-based composites by following a percolation scaling law of the form sigma = sigma(0)(Phi - Phi(c))t. Thermal conductivity assessments as function of MWCNT concentration and temperature is then carried out by modulated temperature dynamic scanning calorimetly (MDSC) in both nanocomposites. In analogy with the electrical properties, no thermal percolation behaviour is pointed out despite noteworthy increases above 1 wt.% MWCNT incorporated in PES and phenoxy and temperature dependence below glass transition temperature. The effect of gas purge is also considered and reveals to be meaningful in relation with the thermal conductivity values of MWCNT-reinforced PES and phenoxy nanocomposites. Afterwards, a comparison of the DSC technique results byMDSC is performed with a thermal conductivity measurement using a Hot Disk transient technique showing significant discordance in experimental data, sometimes over the range of +/- 15%. (c) 2013 Elsevier Ltd. All rights reserved.