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- ItemElectrical and melt rheological characterization of PC and co-continuous PC/SAN blends filled with CNTs: Relationship between melt-mixing parameters, filler dispersion, and filler aspect ratio(Hoboken, NJ [u.a.] : Wiley, 2018) Liebscher, Marco; Domurath, Jan; Krause, Beate; Saphiannikova, Marina; Heinrich, Gert; Pötschke, PetraElectrical and melt rheological properties of melt-mixed polycarbonate (PC) and co-continuous PC/poly(styrene–acrylonitrile) (SAN) blends with carbon nanotubes (CNTs) are investigated. Using two sets of mixing parameters, different states of filler dispersion are obtained. With increasing CNT dispersion, an increase in electrical resistivity near the percolation threshold of PC–CNT composites and (PC + CNT)/SAN blends is observed. This suggests that the higher mixing energies required for better dispersion also result in a more severe reduction of the CNT aspect ratio; this effect was proven by CNT length measurements. Melt rheological studies show higher reinforcing effects for composites with worse dispersion. The Eilers equation, describing the melt viscosity as function of filler content, was used to fit the data and to obtain information about an apparent aspect ratio change, which was in accordance with measured CNT length reduction. Such fitting could be also transferred to the blends and serves for a qualitatively based discussion. © 2017 Wiley Periodicals
- ItemInfluence of talc with different particle sizes in melt-mixed LLDPE/MWCNT composites(Hoboken, NJ [u.a.] : Wiley, 2013) Müller, Michael Thomas; Dreyße, Janine; Häußler, Liane; Krause, Beate; Pötschke, PetraLinear low-density polyethylene (LLDPE) was melt-mixed with multiwalled carbon nanotubes (MWCNTs) and varying amounts of three different kinds of talc (phyllo silicate), each with a different particle size distribution, to examine the effect of these filler combinations with regards to the electrical percolation behavior. The state of the filler dispersion was assessed using transmission light microscopy and electron microscopy. The use of talc as a second filler during the melt mixing of LLDPE/MWCNT composites resulted in an improvement in the dispersion of the MWCNTs and a decrease of the electrical percolation threshold. Talc with lower particle sizes showed a more pronounced effect than talc with larger particle sizes. However, the improvement in dispersion was not reflected in the mechanical properties. Modulus and stress values increase with both, MWCNT and talc addition, but not in a synergistic manner. The crystallization behavior of the composites was studied by differential scanning calorimetry to determine its potential influence on the electrical percolation threshold. It was found that the crystallinity of the matrix increased slightly with the addition of talc but no further increments were observed with the incorporation of the MWCNTs. © 2013 Wiley Periodicals, Inc.
- ItemEffects of high energy electrons on the properties of polyethylene / multiwalled carbon nanotubes composites: Comparison of as-grown and oxygen-functionalised MWCNT(Melville, NY : AIP, 2014) Krause, Beate; Pötschke, Petra; Gohs, U.Polymer modification with high energy electrons (EB) is well established in different applications for many years. It is used for crosslinking, curing, degrading, grafting of polymeric materials and polymerisation of monomers. In contrast to this traditional method, electron induced reactive processing (EIReP) combines the polymer modification with high energy electrons and the melt mixing process. This novel reactive method was used to prepare polymer blends and composites. In this study, both methods were used for the preparation of polyethylene (PE)/ multiwalled carbon nanotubes (MWCNT) composites in the presence of a coupling agent. The influence of MWCNT and type of electron treatment on the gel content, the thermal conductivity, rheological, and electrical properties was investigated whereby as-grown and oxidised MWCNT were used. In the presence of a coupling agent and at an absorbed dose of 40 kGy, the gel content increased from 57 % for the pure PE to 74 % or 88 % by the addition of as-grown (Baytubes® C150P) or oxidised MWCNT, respectively. In comparison to the composites containing the as-grown MWCNTs, the use of the oxidised MWCNTs led to higher melt viscosity and higher storage modulus due to higher yield of filler polymer couplings. The melt viscosity increased due to the addition of MWCNT and crosslinking of PE. The thermal conductivity increased to about 150 % and showed no dependence on the kind of MWCNT and the type of electron treatment. In contrast, the lowest value of electrical volume resistivity was found for the non-irradiated samples and after state of the art electron treatment without any influence of the type of MWCNT. In the case of EIReP, the volume resistivity increased by 2 (as-grown MWCNT) or 3 decades (oxidised MWCNT) depending on the process parameters. © 2014 American Institute of Physics.
- ItemMelt mixed composites of polypropylene with singlewalled carbon nanotubes for thermoelectric applications: Switching from p- to n-type behavior by additive addition(Melville, NY : AIP, 2019) Pötschke; Petra; Krause, Beate; Luo, JinjiComposites were prepared with polypropylene (PP) as the matrix and singlewalled CNTs (SWCNTs) of the type TUBALL from OCSiAl Ltd. as the conducting component by melt processing in a small-scale twin-screw compounder. In order to switch the typical p-type behavior of such composites from positive Seebeck coefficients (S) into n-type behavior with negative Seebeck coefficients, a non-ionic surfactant polyoxyethylene 20 cetyl ether (Brij58) was used and compared with a PEG additive, which was shown previously to be able to induce such switching. For PP-2 wt% SWCNT composites Brij58 is shown to result in n-type composites. The negative S values (up to −48.2 µV/K) are not as high as in the case of previous results using PEG (−56.6 µV/K). However, due to the more pronounced effect of Brij58 on the electrical conductivity, the achieved power factors are higher and reach a maximum of 0.144 µW/(m·K2) compared to previous 0.078 µW/(m·K2) with PEG. Dispersion improvement depends on the type of SWCNTs obtained by using varied synthesis/treatment conditions. Solution prepared composites of PEG with SWCNTs also have negative S values, indicating the donation of electrons from PEG to the SWCNTs. However, such composites are brittle and not suitable as thermoelectric materials.
- ItemEffect of additives on MWCNT dispersion and electrical percolation in polyamide 12 composites(Melville, NY : AIP, 2017) Socher, Robert; Krause, Beate; Pötschke, PetraThe 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.
- ItemInfluence of graphite and SEBS addition on thermal and electrical conductivity and mechanical properties of polypropylene composites(Melville, NY : AIP, 2017) Krause, Beate; Cohnen, A.; Pötschke, Petra; Hickmann, T.; Koppler, D.; Proksch, B.; Kersting, T.; Hopmann, C.In this study, composites based on polypropylene (PP) and different graphite fillers were melt mixed using small scale microcompounder Xplore DSM15 as well as lab-scale co-rotating twin screw extruder Coperion ZSK26Mc. The measurements of the electrical and thermal conductivity as well as mechanical properties of the composites were performed on pressed plates. It was found that the addition of graphite powders having different particle size distributions leads to different increases of the thermal conductivity. For synthetic graphite, the PP composites filled with TIMCAL Timrex® KS500 reached the highest value of thermal conductivity of 0.52 W/(m·K) at 10 vol% loading, whereas this composite was not electrical conductive. Furthermore, the influence of a styrene-ethylene-butylene-styrene block copolymer (SEBS) based impact modifier on the mechanical properties of PP filled with 80 wt% of different synthetic graphites was investigated. For that the proportion of SEBS in the PP component was varied systematically. The conductivities were influenced by the type of graphite and the content of impact modifier. The results indicate that the impact strength of the composite containing TIMCAL Timrex® KS300-1250 can be increased by approx. 100 % when replacing 50 wt% of the PP component by SEBS.
- ItemAspect ratio effects of multi-walled carbon nanotubes on electrical, mechanical, and thermal properties of polycarbonate/MWCNT composites(Hoboken, NJ [u.a.] : Wiley, 2014) Guo, Jiaxi; Liu, Yanjun; Prada-Silvy, Ricardo; Tan, Yongqiang; Azad, Samina; Krause, Beate; Pötschke, Petra; Grady, Brian P.Two multi-walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin-screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ∼100. Transmission electron microscopy results suggest that melt-mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt-mixing. Molecular weight measurements show that during melt-mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ∼100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc.
- ItemExtruded polycarbonate/Di-Allyl phthalate composites with ternary conductive filler system for bipolar plates of polymer electrolyte membrane fuel cells(Bristol : IOP Publ., 2019) Naji, Ahmed; Krause, Beate; Pötschke, Petra; Ameli, AmirHere, we report multifunctional polycarbonate (PC)-based conductive polymer composites (CPCs) with outstanding performance manufactured by a simple extrusion process and intended for use in bipolar plate (BPP) applications in polymer electrolyte membrane (PEM) fuel cells. CPCs were developed using a ternary conductive filler system containing carbon nanotube (CNT), carbon fiber (CF), and graphite (G) and by introducing di-allyl phthalate (DAP) as a plasticizer to PC matrix. The samples were fabricated using twin-screw extrusion followed by compression molding and the microstructure, electrical conductivity, thermal conductivity, and mechanical properties were investigated. The results showed a good dispersion of the fillers with some degree of interconnection between dissimilar fillers. The addition of DAP enhanced the electrical conductivity and tensile strength of the CPCs. Due to its plasticizing effect, DAP reduced the processing temperature by 75 °C and facilitated the extrusion of CPCs with filler loads as high as 63 wt% (3 wt% CNT, 30 wt% CF, 30 wt% G). Consequently, CPCs with the through-plane electrical, in-plane electrical and thermal conductivities and tensile strength of 4.2 S cm-1, 34.3 S cm-1, 2.9 W m-1 K-1, and 75.4 MPa, respectively, were achieved. This combination of properties indicates the potential of PC-based composites enriched with hybrid fillers and plasticizers as an alternative material for BPP application.
- ItemInfluence 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, PetraIn 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.
- ItemPolymer - Carbon nanotube composites for thermoelectric applications(Melville, NY : AIP, 2017) Luo, J.; Krause, Beate; Pötschke, PetraThe thermoelectric (TE) performance of electrically conductive thermoplastic composites prepared by melt mixing was investigated. A cost effective widely used in industry polymer, namely polypropylene (PP), was chosen as the matrix to fabricate the composites. Singlewalled carbon nanotubes (SWCNTs), the amount (2 wt%) of which was selected to be above the electrical percolation threshold (< 0.2 wt%), were used to form an electrical conducting network. Besides as-produced SWCNTs plasma modified tubes were employed to study the influence of the functionalization on the morphology, dispersion and TE properties of the PP composites. In addition, melt processing conditions, e.g. temperature, rotation speed, and time during mixing in a small-scale compounder were varied. Furthermore, an ionic liquid (IL, 1-methyl-3-octylimidazolium tetrafluoroborate) was used as a processing additive during melt mixing, which was confirmed to improve the electrical conductivity of the composites. Simultaneous increase in the Seebeck coefficient up to a value of 64 μV/K was recorded, leading to a much better power factor of 0.26 μW/(m·K2) compared to composites without IL. This melt mixing strategy opens new avenues for solvent-free, large scale fabrication of polymer based TE materials.