In the present study, different quantities of multiwalled carbon nanotubes and an immiscible blend of polyamides, 50 vol%/50 vol%. Polyamide 12/polyamide 6 (PA12/PA6), are melt blending by extrusion to obtain conducting polymer composites. The rheological and electrical properties of nanocomposites are evaluated as function of nanofiller content. Both rheological and electrical percolation thresholds are calculated by graphical methods and fitting the experimental data to the well‐known power‐law expression. The low percolation thresholds are probably due to the high aspect ratio of the nanotubes, kept after the composite processing and to the preferential localization of carbon nanotubes (CNTs) in the polyamides interface. This latter is predicted by the wetting parameter and finally confirmed by TEM micrographs. The mixing strategy followed, by using a PA12 masterbatch and an immiscible blend of polyamides, seems suitable to form a segregated conductive network in the matrix with low CNT quantities. POLYM. COMPOS., 38:2679–2686, 2017. © 2015 Society of Plastics Engineers

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Three different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin-screw extrusion. The rheological and thermal properties were investigated. The rheological characterization of CNFs/PP composites as function of their volume fraction shows different microstructures: percolated and non-percolated behaviors of their CNF's networks. In this work, the laser flash technique is employed in the experimental determination of the thermal diffusivity and conductivity of composites at room temperature. The ultimate aim is to correlate microstructure described by rheological analysis with final thermal properties. The results show that thermal diffusivity and conductivity are clearly higher for rheologically percolated composites suggesting that above certain critical content of nanofibers thermal transport is mainly controlled by percolated structures caused by interconnected CNFs' networks. Finally, thermal conductivity results are described by means of percolation theory from which an intrinsic thermal conductivity for the CNFs' network of approximately 6.5 W/ m K, i.e. close to three times lower than some values reported in literature for SWCNTs' networks, was calculated.

The structure-properties relationships of a polyamide 12 (PA12)/polyamide 6 (PA6) blend containing multiwalled carbon nanotubes have been investigated as a function of nanofiller amount. The influence of the filler content in the water diffusion behavior of the immiscible PA12/PA6 blend is studied. An acceptable dispersion level of nanotubes in polymer matrix is observed by scanning electron microscopy. The water uptake at saturation, normalized to the polyamide mass, decreases, and the diffusion rate is slower in CNT composites. The enhancement is in line with the increase in stiffness measured in rheological tests. This behavior is related with the rise in the overall crystallinity of the polymer matrix and the selective migration of CNT towards PA6 (more hygroscopic than PA12). These findings display a substantial improvement in respect to the water uptake behavior of pristine PA6 and PA6/CNT composites, expanding the potential applications of composites.

Effect of multiwalled carbon nanotubes in thermal conductivity of an immiscible blend of polyamides, 50/50 (wt%/wt%) polyamide 12/polyamide 6, was analyzed as function of nanofiller amount and temperature. Effect of the molding temperature in the structure of conductive network was investigated by rheology. Data show that 5 vol% multiwalled carbon nanotubes caused an increase of 41% in thermal diffusivity and 78% in thermal conductivity respect to polyamide blend values. Thermal conductivity improvement could be described by percolation theory, with a low threshold composition (φc = 0.09 vol% carbon nanotube). Fitting parameters obtained from Agari’s adjustment model show that polyamides structure is not affected by carbon nanotubes and the nanofillers can easily form conductive paths in the polyamide 12/polyamide 6 matrix. The temperature increase facilitates nanofiller dispersion causing the formation of a denser carbon nanotube network and rising the thermal diffusivity of carbon nanotube composites with low percolation level, as was proved on annealed samples at 255℃.