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- ItemAchieving electrical conductive tracks by laser treatment of non-conductive polypropylene/polycarbonate blends filled with MWCNTs(Weinheim : Wiley-VCH, 2014) Liebscher, Marco; Krause, Beate; Pötschke, Petra; Barz, Andrea; Bliedtner, Jens; Möhwald, Michael; Letzsch, AlexanderElectrical non-conductive polymer blends consisting of a polypropylene (PP) matrix and dispersed particles of polycarbonate (PC) were melt compounded with 3 wt.% multiwalled carbon nanotubes (MWCNTs) loading and processed into plates by injection molding. The morphological analysis confirmed the selective localization of the MWCNTs in the PC component. By local irradiation with a CO2 laser beam, depending on the laser conditions, conductive tracks with dimensions of about 2 mm width, 80 to 370 μm depth and line resistances as low as 1.5 kΩ · cm-1 were created on the surface of the non-conductive plates. The factors affecting the line resistance are the PC content, the laser speed and laser power, as well as laser direction with respect to the melt flow direction. After the irradiation an enrichment of MWCNTs in the laser lines was detected indicating that conductive paths were generated by percolation of nanotubes selectively within these lines in otherwise non-conductive plates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemInterfacial chemistry using a bifunctional coupling agent for enhanced electrical properties of carbon nanotube based composites(Oxford : Elsevier Science, 2013) Socher, Robert; Jakisch, Lothar; Krause, Beate; Oertel, Ulrich; Voit, Brigitte; Pötschke, PetraA bifunctional coupling agent (BCA) containing one oxazoline and one benzoxazinone group was applied to promote a reaction between polyamide 12 (PA12) and multiwalled carbon nanotubes (MWCNTs) during melt mixing. With this modification, the MWCNT content needed for the electrical percolation was significantly reduced by more than a factor of three. For amino functionalized MWCNT-PA12 composites adding 1 wt.% BCA electrical percolation was reached at only 0.37 wt.% MWCNTs compared to 1.0 wt.% without BCA. With the help of a model reaction, the covalent attachment of the BCA to the MWCNTs could be shown by thermogravimetric analysis (TGA) and via fluorescence spectroscopy. Model compounds were applied containing either only the oxazoline or the benzoxazinone group to show that the better electrical properties in the PA12-MWCNT composites were a result of a covalent bond between the polymer and the nanotube which only takes place when the BCA was used. In addition, significantly higher electrical conductivity values were obtained by the addition of BCA as well with amino functionalized as with nonmodified commercial MWCNTs. This surprising result was attributed to the significant hydroxy group content on the surface of those commercial MWCNTs. © 2013 Elsevier Ltd. All rights reserved.
- ItemDispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions(Oxford : Elsevier Science, 2014) Staudinger, Ulrike; Krause, Beate; Steinbach, Christine; Pötschke, Petra; Voit, BrigitteThe dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloroform and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions.
- ItemMelt mixed PCL/MWCNT composites prepared at different rotation speeds: Characterization of rheological, thermal, and electrical properties, molecular weight, MWCNT macrodispersion, and MWCNT length distribution(Oxford : Elsevier Science, 2013) Pötschke, Petra; Villmow, Tobias; Krause, BeateComposites of poly(caprolactone) (PCL) and 0.5 wt.% multiwalled carbon nanotubes (MWCNT) were prepared by melt-mixing in a conical twin-screw micro-compounder by varying the rotation speed between 25 and 400 rpm at constant mixing time and temperature. The state of dispersion analyzed by light microscopy was improved with increasing rotation speed but levels off starting at about 100 rpm. PCL molecular weight as well as crystallization and melting behavior did show only insignificant difference when varying the rotation speed. Concerning melt rheological properties, storage modulus G′ and complex viscosity η* at 0.1 rad/s increased up to a rotation speed of about 75 rpm illustrating improved dispersion. When further increasing the speed G′ and η* decreased which was attributed to more pronounced nanotube shortening as quantified by TEM measurements. Both effects - improved dispersion and nanotube shortening - are also reflected in the electrical resistivity values of compression molded samples which show a minimum of resistivity at the rotation speed of 75 rpm corresponding to a specific mechanical energy input of 0.47 kWh/kg. © 2013 Elsevier Ltd. All rights reserved.
- ItemLocalization of carbon nanotubes in polyamide 6 blends with non-reactive and reactive rubber(Oxford : Elsevier Science, 2014) Krause, Beate; Schneider, Cecile; Boldt, Regine; Weber, Martin; Park, Hye Jin; Pötschke, PetraBlending of two immiscible polymer matrices can be an effective way to combine favourable properties of both blend partners. The additional incorporation of multiwalled carbon nanotubes (MWCNTs) in such thermoplastic blends may further enhance the blend properties and especially generate electrical conductivity. In the present study, 20 wt.% of non-reactive rubber and maleic anhydride functionalized rubber were melt blended with polyamide 6 and 3 wt.% MWCNTs by using different incorporation strategies. For the blends containing non-reactive rubber, the MWCNTs were always localized selectively in the thermodynamically preferred polyamide phase as shown by TEM images and electrical measurements. Interestingly, the different strategies resulted in different localization behaviours of the MWCNTs in case of the reactive rubber. These findings demonstrate the significant influence of maleic anhydride groups of the rubber component on localization of MWCNTs in the different blend phases which results in different values of electrical volume resistivity of the blends. © 2014 The Authors. Published by Elsevier Ltd.