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Now showing 1 - 7 of 7
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    Improvement of carbon nanotube dispersion in thermoplastic composites using a three roll mill at elevated temperatures
    (Barking : Elsevier, 2013) Pötschke, Petra; Krause, Beate; Buschhorn, Samuel T.; Köpke, Ulf; Müller, Michael T.; Villmow, Tobias; Schulte, Karl
    The paper reports the effect of using of a three roll mill as additional dispersion step after twin-screw melt extrusion of nanocomposites containing thermoplastic polymers and multiwalled carbon nanotubes. The three roll milling technology was adapted to elevated temperatures of up to 180 °C and examples are shown for its use in processing of different pre-compounded thermoplastic polymer composites based on polypropylene, polycaprolactone and ethylene-vinyl acetate. The aim is to enhance the state of dispersion achieved by the previous melt extrusion step. In particular, depending on the state of dispersion before three roll milling and the adapted conditions, like number of runs and gap sizes, a reduction of number and size of remaining primary nanotube agglomerates was found. This was studied using light microscopy. The resulting improvements in mechanical properties were assessed and could be attributed to the improved dispersion. In some cases agglomerate free samples could be achieved after the three roll milling process. © 2012 Elsevier Ltd.
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    Influence of feeding conditions in twin-screw extrusion of PP/MWCNT composites on electrical and mechanical properties
    (Barking : Elsevier, 2011) Müller, Michael Thomas; Krause, Beate; Kretzschmar, Bernd; Pötschke, Petra
    The influence of feeding conditions of multiwalled carbon nanotube (MWCNT) materials, namely Baytubes® C150P and Nanocyl™ NC7000, into polypropylene (PP) was investigated with respect to achieving suitable nanotube dispersion, high electrical conductivity, and good mechanical properties. Both MWCNT materials were fed at selected concentrations either in the hopper of the twin-screw extruder or using a side feeder under otherwise identical extrusion conditions (rotation speed, throughput, temperature profile) using a Berstorff ZE 25 twin-screw extruder. Afterwards, injection molding was performed under identical conditions. The results indicate that the more compact Baytubes® C150P agglomerates should be added into the hopper, as the dispersion assessed by light microscopy is better, electrical resistivities measured on compression and injection molded samples are lower, and elastic modulus, yield strength and impact strength are higher as compared to side feeding. On the other hand, for the more loosely packed Nanocyl™ NC7000 agglomerates, addition using the side feeder leads to better dispersion, lower electrical resistivity, and higher mechanical properties. © 2011 Elsevier Ltd.
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    Influence of dry grinding in a ball mill on the length of multiwalled carbon nanotubes and their dispersion and percolation behaviour in melt mixed polycarbonate composites
    (Barking : Elsevier, 2011) Krause, Beate; Villmow, Tobias; Boldt, Regine; Mende, Mandy; Petzold, Gudrun; Pötschke, Petra
    Ball milling of carbon nanotubes (CNTs) in the dry state is a common way to produce tailored CNT materials for composite applications, especially to adjust nanotube lengths. For NanocylTM NC7000 nanotube material before and after milling for 5 and 10h the length distributions were quantified using TEM analysis, showing decreases of the mean length to 54% and 35%, respectively. With increasing ball milling time in addition a decrease of agglomerate size and an increase of packing density took place resulting in a worse dispersability in aqueous surfactant solutions. In melt mixed CNT/polycarbonate composites produced using masterbatch dilution step, the electrical properties, the nanotube length distribution after processing, and the nano- and macrodispersion of the nanotubes were studied. The slight increase in the electrical percolation threshold in the melt mixed composites with ball milling time of CNTs can be assigned to lower nanotube lengths as well as the worse dispersability of the ball milled nanotubes. After melt compounding, the mean CNT lengths were shortened to 31%, 50%, and 66% of the initial lengths of NC7000, NC7000-5h, and NC7000-10h, respectively. © 2011 Elsevier Ltd.
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    Electrical and thermal properties of polyamide 12 composites with hybrid fillers systems of multiwalled carbon nanotubes and carbon black
    (Barking : Elsevier, 2011) Socher, Robert; Krause, Beate; Hermasch, Sylvia; Wursche, Roland; Pötschke, Petra
    Hybrid filler systems of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) were incorporated into two types of polyamide 12 (PA12) using small-scale melt mixing in order to identify potential synergistic effects on the interaction of these two electrical conductive fillers. Although no synergistic effects were observed regarding the electrical percolation threshold, at loadings well above the percolation threshold higher volume conductivities were obtained for samples containing both, MWCNT and CB, as compared to single fillers. This effect was more pronounced when using a higher viscous PA12 matrix. The formation of a co-supporting network can be assumed. The combined use of CB and MWCNTs improved the macrodispersion of MWCNT agglomerates, which can be assigned as a synergistic effect. DSC measurements indicated an effect of the nanofiller on crystallisation temperatures of PA12; however this was independent of the kind or amount of the carbon nanofiller. © 2011 Elsevier Ltd.
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    Ultralow percolation threshold in polyamide 6.6/MWCNT composites
    (Barking : Elsevier, 2015) Krause, Beate; Boldt, Regine; Häußler, Liane; Pötschke, Petra
    When incorporating multiwalled carbon nanotubes (MWCNTs) synthesised by the aerosol-CVD method using different solvents into polyamide 6.6 (PA66) by melt mixing an ultralow electrical percolation threshold of 0.04. wt.% was found. This very low threshold was assigned to the specific characteristic of the MWCNTs for which a very high aspect ratio, a good dispersability in aqueous surfactant dispersions, and relatively low oxygen content near the surface were measured. The investigation of the composites by transmission electron microscopy on ultrathin cuts as well as by scanning electron microscopy combined with charge contrast imaging on compression moulded plates illustrated a good MWCNT dispersion within the PA66 matrix and that the very high aspect ratio of the nanotubes remained even after melt processing. Additionally, the thermal behaviour of the PA66 composites was investigated using differential scanning calorimetry (DSC) showing that the addition of only 0.05. wt.% MWCNT leads to an increase of the onset crystallization temperature of 11. K.
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    Melt mixed nano composites of PA12 with MWNTs: Influence of MWNT and matrix properties on macrodispersion and electrical properties
    (Barking : Elsevier, 2011) Socher, Robert; Krause, Beate; Boldt, Regine; Hermasch, Sylvia; Wursche, Roland; Pötschke, Petra
    Nanocomposites containing four different polyamide 12 (PA12) types and three grades of multiwalled carbon nanotubes (MWNTs) were prepared via small-scale melt processing to study the effect of different MWNTs and the influence of polymer properties on the dispersion of the fillers and the electrical properties of the composites. Under the selected mixing conditions the lowest electrical percolation threshold of 0.7. wt.% was found for Nanocyl™ NC7000 in low viscous PA12. Moreover, big influences of the end group functionality (acid or amine excess) and the melt viscosity of the matrix were found. Composites of PA12 with acid excess showed lower percolation thresholds than those based on amine terminated materials. At constant end group ratio low viscous matrices resulted in lower percolation thresholds than high viscous materials. The best MWNT dispersion was obtained in both high viscous PA12 composites. In these systems the mixing speed was varied indicating an optimum concerning electrical conductivity at 150 rpm as compared to 50 and 250 rpm. © 2010 Elsevier Ltd.
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    Influence of different carbon nanotubes on the electrical and mechanical properties of melt mixed poly(ether sulfone)-multi walled carbon nanotube composites
    (Barking : Elsevier, 2012) Chakraborty, Sourav; Pionteck, Jürgen; Krause, Beate; Banerjee, Susanta; Voit, Brigitte
    Commercial Udel® poly(ether sulfone) (PSU) was filled with three different commercially available multiwalled carbon nanotubes (MWCNTs) by small scale melt mixing. The MWCNTs were as grown NC 7000 and two of its derivatives prepared by ball milling treatment. One of them was unmodified (NC 3150); the other was amino modified (NC 3152). The main difference beside the reactivity was the reduced aspect ratio of NC 3150 and NC 3152 caused by ball milling process. All PSU/MWCNT composites with similar filler content were prepared under fixed processing conditions and comparative analysis of their electrical and mechanical properties were performed and were correlated with their microstructure, characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A non-uniform MWCNT dispersion was observed in all composites. The MWCNTs were present in form of agglomerates in the size of 10-60. μm whereas the deagglomerated part was homogeneously distributed in the PSU matrix. The differences in the agglomeration states correlate with the variations of properties between different PSU/MWCNT composites. The lowest electrical percolation threshold of 0.25-0.5. wt.% was observed for the shortened non-functionalized MWCNT composites and the highest for amine-modified MWCNT composites (ca. 1.5. wt.%). The tensile behavior of the three composites was only slightly altered with CNT loading as compared to the pure PSU. However, the elongation at break showed a reduction with MWCNT loading and the reduction was least for composite with best MWCNT dispersion. © 2012 Elsevier Ltd.