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Author: Krause, Beate × Publisher: Oxford : Elsevier Science × Subject: Polymer-matrix composites ×

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    Melt 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, Beate
    Composites 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.
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    Interfacial 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, Petra
    A 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.