Superposition approach for description of electrical conductivity in sheared MWNT/polycarbonate melts

The theoretical description of electrical properties of polymer melts, filled with attractively interacting conductive particles, represents a great challenge. Such filler particles tend to build a network-like structure which is very fragile and can be easily broken in a shear flow with shear rates of about 1 s–1. In this study, measured shear-induced changes in electrical conductivity of polymer composites are described using a superposition approach, in which the filler particles are separated into a highly conductive percolating and low conductive non-percolating phases. The latter is represented by separated well-dispersed filler particles. It is assumed that these phases determine the effective electrical properties of composites through a type of mixing rule involving the phase volume fractions. The conductivity of the percolating phase is described with the help of classical percolation theory, while the conductivity of non-percolating phase is given by the matrix conductivity enhanced by the presence of separate filler particles. The percolation theory is coupled with a kinetic equation for a scalar structural parameter which describes the current state of filler network under particular flow conditions. The superposition approach is applied to transient shear experiments carried out on polycarbonate composites filled with multi-wall carbon nanotubes

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred

Establishment, morphology and properties of carbon nanotube networks in polymer melts

As for nanofillers in general, the properties of carbon nanotube (CNT) -polymer composites depend strongly on the filler arrangement and the structure of the filler network. This article reviews our actual understanding of the relation between processing conditions, state of CNT dispersion and structure of the filler network on the one hand, and the resulting electrical, melt rheological and mechanical properties, on the other hand. The as-produced rather compact agglomerates of CNTs (initial agglomerates, >1 μm), whose structure can vary for different tube manufacturers, synthesis and/or purification conditions, have first to be well dispersed in the polymer matrix during the mixing step, before they can be arranged to a filler network with defined physical properties by forming secondary agglomerates. Influencing factors on the melt dispersion of initial agglomerates of multi-walled CNTs into individualized tubes are discussed in context of dispersion mechanisms, namely the melt infiltration into initial agglomerates, agglomerate rupture and nanotube erosion from agglomerate surfaces. The hierarchical morphology of filler arrangement resulting from secondary agglomeration processes has been found to be due to a competition of build-up and destruction for the actual melt temperature and the given external flow field forces. Related experimental results from in-line and laboratory experiments and a model approach for description of shear-induced properties are presented

The influence of injection molding parameters on electrical properties of PC/ABS-MWCNT nanocomposites

[EN] The influence of injection molding parameters on electrical properties and morphology of PC/ABS-MWCNT nanocomposites is presented in this article. Investigation is based on the masterbatch of 5.0wt% carbon nanotubes obtained by melt-mixing. Further processing includes dilution of this nanocomposite to desired concentrations on twin-screw extruder and injection molding or direct dilution of masterbatch in injection molding. Additionally, reprocessing of materials formed by compression and injection molding is presented along with the change in electrical conductivity. Morphology differs strongly between the two processing paths showing change in agglomeration behavior between nanotubes concentrations. Electrical properties show dependence on injection velocity and melt temperature in both applied processing paths. Moreover, electrical conductivity recovery is proved after injection and compression molding.This work is funded by the European Community's Seventh Framework Program (FP7-PEOPLE-ITN-2008) within the CONTACT project Marie Curie Fellowship under grant number 238363. The authors would like to thank to Javier Gomez (SCIC, University Jaume I of Castellon) for support with electron microscopy measurements.Wegrzyn, M.; Juan Nadal, S.; Benedito, A.; Giménez Torres, E. (2013). The influence of injection molding parameters on electrical properties of PC/ABS-MWCNT nanocomposites. Journal of Applied Polymer Science. 130(3):2152-2158. https://doi.org/10.1002/app.39412S215221581303Pötschke, P., Dudkin, S. M., & Alig, I. (2003). Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites. Polymer, 44(17), 5023-5030. doi:10.1016/s0032-3861(03)00451-8Duong, H. M., Yamamoto, N., Bui, K., Papavassiliou, D. V., Maruyama, S., & Wardle, B. L. (2010). 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Influence of injection molding parameters on the electrical resistivity of polycarbonate filled with multi-walled carbon nanotubes. Composites Science and Technology, 68(3-4), 777-789. doi:10.1016/j.compscitech.2007.08.031Richter, S., Saphiannikova, M., Jehnichen, D., Bierdel, M., & Heinrich, G. (2009). Experimental and theoretical studies of agglomeration effects in multi-walled carbon nanotube-polycarbonate melts. Express Polymer Letters, 3(12), 753-768. doi:10.3144/expresspolymlett.2009.94Pegel, S., Pötschke, P., Petzold, G., Alig, I., Dudkin, S. M., & Lellinger, D. (2008). Dispersion, agglomeration, and network formation of multiwalled carbon nanotubes in polycarbonate melts. Polymer, 49(4), 974-984. doi:10.1016/j.polymer.2007.12.024Park, D. H., Yoon, K. H., Park, Y.-B., Lee, Y. S., Lee, Y. J., & Kim, S. W. (2009). Electrical resistivity of polycarbonate/multiwalled carbon nanotube composites under varying injection molding conditions. 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Journal of Applied Polymer Science, 120(1), 70-78. doi:10.1002/app.32983Cipriano, B. H., Kota, A. K., Gershon, A. L., Laskowski, C. J., Kashiwagi, T., Bruck, H. A., & Raghavan, S. R. (2008). Conductivity enhancement of carbon nanotube and nanofiber-based polymer nanocomposites by melt annealing. Polymer, 49(22), 4846-4851. doi:10.1016/j.polymer.2008.08.05

Morphology, Mechanical Performance and Nanoindentation Behavior of Injection Molded PC/ABS-MWCNT Nanocomposites

"This is the peer reviewed version of the following article: Wegrzyn, M., Sahuquillo, O., Benedito, A., & Gimenez, E. (2015). Morphology, mechanical performance, and nanoindentation behavior of injection molded PC/ABS‐MWCNT nanocomposites. Journal of Applied Polymer Science, 132(22), which has been published in final form at https://doi.org/10.1002/app.42014. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] In this work, nanocomposites of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) with various loads of multiwall carbon nanotubes (MWCNT) are investigated. Material is previously formed by masterbatch dilution approach and further processed by injection molding at various velocities. Microscopic characterization of nanocomposites morphology reveals stronger dependence of MWCNT dispersion on processing parameters at higher nanofiller load. Dispersion of carbon nanotubes at various distances from the injection gate is studied by Raman spectroscopy showing lower deviation at elevated injection velocity. Nanoindentation results that are in agreement with uniaxial tensile testing show a slight decrease of nanocomposites¿ mechanical performance at 3.0 wt % MWCNT in samples injected at reduced velocity. This is explained by the increase of agglomeration behavior at these conditions.This work is funded by the European Community's Seventh Framework Program (FP7-PEOPLE-ITN-2008) within the CONTACT project Marie Curie Fellowship under grant number 238363.Wegrzyn, M.; Sahuquillo, O.; Benedito, A.; Giménez Torres, E. (2015). Morphology, Mechanical Performance and Nanoindentation Behavior of Injection Molded PC/ABS-MWCNT Nanocomposites. Journal of Applied Polymer Science. 132(22):1-8. https://doi.org/10.1002/app.42014S1813222Alig, I., Lellinger, D., Engel, M., Skipa, T., & Pötschke, P. (2008). 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Role of processing history on the mechanical and electrical behavior of melt-compounded polycarbonate-multiwalled carbon nanotube nanocomposites

This work investigates the effects of primary compounding temperature and secondary melt processes on the mechanical response and electrical resistivity of polycarbonate filled with 3 wt % multiwalled carbon nanotubes (CNT). Nanocomposites were melt compounded in an industrial setting at a range of temperatures, and subsequently either injection molded or compression molded to produce specimens for the measurement of electrical resistivity, surface hardness, and uniaxial tensile properties. Secondary melt processing was found to be the dominant process in determining the final properties. The effects observed have been attributed to structural arrangements of the CNT network as suggested by morphological evidence of optical microscopy and resistivity measurements. Properties were found to be relatively insensitive to compounding temperature. The measured elastic moduli were consistent with existing micromechanical models