HNBR and its MWCNT reinforced nanocomposites: Crystalline morphology and electrical response

•Crystallinity of HNBR and MWCNT/HNBR systems increases with the addition of MWCNTs.•Recorded relaxations are related to the polymer matrix and the presence of MWCNTs.•Electrical conductivity increases with MWCNT content and frequency.•Effect of temperature, upon ε′ and σ, is more pronounced at low frequencies.

Morphology and electrical response of hydrogenated acrylonitrile butadiene rubber (HNBR) and its multiwall carbon nanotube (MWCNT) reinforced nanocomposites were studied by means of X-ray diffraction and broadband dielectric spectroscopy. HNBR systems were found to be semi-crystalline, with their crystallinity to increase with the addition of MWCNTs. In their dielectric spectra, four relaxation processes were detected. Ascending in relaxation time, these were attributed to: (i) interfacial polarization at the interface of crystalline and amorphous regions of HNBR and at the interface between HNBR and MWCNTs, (ii) glass to rubber transition of the amorphous part of HNBR, (iii) rearrangement of polar side groups, such as –CN, and (iv) local motions of small segments of the main elastomer chain.Electrical conductivity increases with MWCNT content and frequency increment. The effect of temperature, on the electrical response, is more pronounced at low frequencies. The temperature dependence of the electrical conductivity strongly deviates from a pure Arrhenius behavior, signifying that the occurring conductance mechanisms do not correspond to a single thermally activated process. Relaxation dynamics imply that crystalline regions exert motion restrictions to large segments of the macromolecules in the amorphous phase and to polar parts of the systems.

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