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Subject: Electrical resistivity × Subject: Konferenzschrift × WGL Institute: IPF ×

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Now showing 1 - 3 of 3
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    Effect of additives on MWCNT dispersion and electrical percolation in polyamide 12 composites
    (Melville, NY : AIP, 2017) Socher, Robert; Krause, Beate; Pötschke, Petra
    The aim of this study was to decrease the electrical percolation threshold of multiwalled carbon nanotubes (MWCNTs) in a polyamide 12 matrix by the use of additives. Different kinds of additives were selected which either interact with the π-system of the MWCNTs (imidazolium based ionic liquid (IL) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)) or improve the MWCNT wettability (cyclic butylene terephthalate, CBT). The composites were melt mixed using a DACA microcompounder. The electrical percolation threshold for PA12/MWCNT without additives, measured on compression molded plates, was found between 2.0 and 2.25 wt%. With all used additives, a significant reduction of the electrical percolation threshold could be achieved. Whereas the addition of IL and CBT resulted in MWCNT percolation at around 1.0 wt%, a slightly higher percolation threshold between 1.0 and 1.5 wt% was found for PTCDA as an additive. Interestingly, the electrical resistivity at higher loadings was decreased by nearly two decades when using CBT and one decade after application of PTCDA, whereas IL did not contribute to lower values in this range. In all cases macrodispersion as assessed by light microscopy was not improved and even worse as compared to non-modified composites. In summary, the results illustrate that these kinds of additives are able to improve the performance of PA12 based MWCNT nanocomposites.
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    Influence of a supplemental filler in twin-screw extruded PP/CNT composites using masterbatch dilution
    (Melville, NY : AIP, 2019) Müller, Michael Thomas; Krause, Beate; Kretzschmar, Bernd; Pötschke, Petra
    In this study commercially available multiwalled carbon nanotubes (2-8 wt.%) were incorporated in polypropylene (PP) by direct powder feeding or by a masterbatch dilution procedure using a twin-screw extruder. The influence of a supplemental, electrical non-conductive talc or electrically conductive carbon black (CB), filler on the resulting composite properties was investigated. In comparison to the direct carbon nanotube (CNT) incorporation the masterbatch dilution step resulted in improved CNT macro dispersion. The use of the supplemental fillers CB or talc does not show a significant influence on the CNT dispersion state. When compared to direct CNT incorporation, the second compounding process involved in masterbatch dilution leads to higher electrical resistivity of injection molded samples. On the other hand, the supplemental fillers talc or CB decreased the electrical resistivity values. With the addition of talc or CB an increase of the Young’s modulus due to the reinforcing effect of the second filler was achieved. However, no synergistic effect between the used supplemental fillers and the CNT on the mechanical properties was obtained.
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    Improvement of electrical resistivity of highly filled graphite/pp composite based bipolar plates for fuel cells by addition of carbon black
    (Melville, NY : AIP, 2019) Krause, Beate; Pötschke, Petra; Hickmann, Thorsten
    Novel material solutions for polymer based bipolar plates in fuel cells require adapted ways to develop suitable material compositions. The common pathway to develop materials with at the same time high electrical as well as thermal conductivity is the use of conductive graphite as filler with contents up to 80-85 wt.%. However, there is a need to develop recipes with maximized conductive behavior at lowest possible content of conductive filler to enhance the mechanical properties and allow good processability. In this study, composites based on polypropylene (PP) and different filler systems were melt-mixed using a lab scale co-rotating twin-screw extruder and compression molded to bipolar type plates. As fillers synthetic (G) or expanded (EG) graphites were incorporated. At the overall filler content of 60 wt.% or 80 wt% part of the graphite was replaced by highly conductive carbon black (CB, 2.5 wt.%, 5.0 wt.%). It was found that the addition of CB significantly reduced the electrical volume as well as the surface resistivity up to values of 0.12 Ωcm or 4 mΩ/square, respectively. For the values of thermal conductivity the kind and particle size of the selected graphite was important. If expanded graphite was partially replaced by CB, the thermal conductivity of PP/EG+CB composites decreased significantly. Otherwise, the combination of synthetic graphite and CB changed the thermal conductivity of PP composites only marginal at the same overall filler content. For both graphite types the filler with larger particle size resulted in higher thermal conductivity.