Carbon-filled polymer blends with triple-continuous structure

To address the issues of the manufacturing cost and concurrent reduction in mechanical properties when a high fiUer concentration is used, carbon-filled polymer blends containing a triple-continuous structure in 3D space have been pursued recently [24-26]. Shown in Fig. 12.1 is the schematic of the carbon-filled polymer blend with a triple-continuous structure, consisting of a binary polymer blend (i.e.. Phases A and B) and CB or CNT particles. Both polymer phases are continuous in 3D space. The conductive carbon is preferentially located in Hiase A and its concentration is... 

The effectiveness of carbon-filled polymer blends in improving simultaneously the electrical conductivity and the mechanical strength has been demonstrated by Shaw. Carbon-filled polymer blends with a triple-continuous structure, consisting of... 

Fig. 12.1 Schematic of the microstructure of carbon-fiHed polymer blends with a triple-continuous structure. (From M. Wu and L. Shaw, A novel concept of carbon-filled polymer blends for applications of PEM fuel cell bipolar plates, Int. J. Hydrogen Energ. 2005 30(4) 373-380, with...

In spite of the substantial progress made with the concept of carbon-filled polymer blends containing a triple-continuous structure, the carbon-filled polymer blends studied so far only contain relatively low carbon concentrations. As a result, their electrical conductivities are still far below the desired values (such as >100 S cm ) for the application of PEM fuel cell bipolar plates. Therefore, it is imperative to investigate (a) whether such a triple-continuous structure can still be injection molded for polymer blends with high carbon concentrations (e.g., >30 vol% carbon) and (b) whether the polymer blends with high carbon concentrations and a triple-continuous structure, if injection moldable, still possess superior electrical conductivity and mechanical properties. Both issues will be the topics of future studies. 

Given that all of the CNT-filled polymer blends in this study are prepared with 50 vol% of the CNT-filled PET phase (with 12 vol% CNTs) plus 50 vol% of the second immiscible polymer phase (with no CNTs), it is reasonable to assume that both the CNT-fiUed PET phase and the second immiscible neat polymer phase have formed self-continuous 3D networks in the polymer blends. This expectation is confirmed by the microstructure examination (see Sect. 12.1), which reveals that the area fractions of the CNT-filled region and the CNT-free region are both near 50%. Furthermore, the electrical conductivity data suggest that the carbon nanotubes within the PET phase have also formed a 3D conductive path because the electrical resistivity has been reduced from the neat polymer blends to the CNT-filled polymer blends by about 12 orders of magnitude. With such a triple-continuous structure, the conductive CNT-filled PET network and the non-conductive second polymer phase can be treated as parallel conductors, and the resulting resistivity, p, of the CNT-filled polymer blend can be estimated using the statistical percolation model proposed by Bueche [61] ... 

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