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- 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.
- ItemThe Localization Behavior of Different CNTs in PC/SAN Blends Containing a Reactive Component(Basel : MDPI, 2021-3-1) Gültner, Marén; Boldt, Regine; Formanek, Petr; Fischer, Dieter; Simon, Frank; Pötschke, PetraCo-continuous blend systems of polycarbonate (PC), poly(styrene-co-acrylonitrile) (SAN), commercial non-functionalized multi-walled carbon nanotubes (MWCNTs) or various types of commercial and laboratory functionalized single-walled carbon nanotubes (SWCNTs), and a reactive component (RC, N-phenylmaleimide styrene maleic anhydride copolymer) were melt compounded in one step in a microcompounder. The blend system is immiscible, while the RC is miscible with SAN and contains maleic anhydride groups that have the potential to reactively couple with functional groups on the surface of the nanotubes. The influence of the RC on the localization of MWCNTs and SWCNTs (0.5 wt.%) was investigated by transmission electron microscopy (TEM) and energy-filtered TEM. In PC/SAN blends without RC, MWCNTs are localized in the PC component. In contrast, in PC/SAN-RC, the MWCNTs localize in the SAN-RC component, depending on the RC concentration. By adjusting the MWCNT/RC ratio, the localization of the MWCNTs can be tuned. The SWCNTs behave differently compared to the MWCNTs in PC/SAN-RC blends and their localization occurs either only in the PC or in both blend components, depending on the type of the SWCNTs. CNT defect concentration and surface functionalities seem to be responsible for the localization differences.
- ItemCuxCo1-xFe2O4 (x = 0.33, 0.67, 1) Spinel Ferrite Nanoparticles Based Thermoplastic Polyurethane Nanocomposites with Reduced Graphene Oxide for Highly Efficient Electromagnetic Interference Shielding(Basel : Molecular Diversity Preservation International (MDPI), 2022-2-26) Anju; Yadav, Raghvendra Singh; Pötschke, Petra; Pionteck, Jürgen; Krause, Beate; Kuřitka, Ivo; Vilčáková, Jarmila; Škoda, David; Urbánek, Pavel; Machovský, Michal; Masař, Milan; Urbánek, MichalCuxCo1-x Fe2O4 (x = 0.33,0.67,1)-reduced graphene oxide (rGO)-thermoplastic polyurethane (TPU) nanocomposites exhibiting highly efficient electromagnetic interference (EMI) shielding were prepared by a melt-mixing approach using a microcompounder. Spinel ferrite Cu0.33Co0.67Fe2O4 (Cu-CoF1), Cu0.67Co0.33Fe2O4 (CuCoF2) and CuFe2O4 (CuF3) nanoparticles were synthesized using the sonochemical method. The CuCoF1 and CuCoF2 exhibited typical ferromagnetic features, whereas CuF3 displayed superparamagnetic characteristics. The maximum value of EMI total shielding effectiveness (SEt) was noticed to be 42.9 dB, 46.2 dB, and 58.8 dB for CuCoF1-rGO-TPU, CuCoF2-rGO-TPU, and CuF3-rGO-TPU nanocomposites, respectively, at a thickness of 1 mm. The highly efficient EMI shielding performance was attributed to the good impedance matching, conductive, dielectric, and magnetic loss. The demonstrated nanocomposites are promising candidates for a lightweight, flexible, and highly efficient EMI shielding material.
- ItemCorrelation of carbon nanotube dispersability in aqueous surfactant solutions and polymers(New York, NY [u.a.] : Pergamon Press, 2009) Krause, Beate; Petzold, Gudrun; Pegel, Sven; Pötschke, PetraIn order to assess the dispersability of carbon nanotube materials, tubes produced under different synthesis conditions were dispersed in aqueous surfactant solutions and the sedimentation behaviour under centrifugation forces was investigated using a LUMiFuge stability analyzer. The electrical percolation threshold of the nanotubes after melt mixing in polyamide 6.6 was determined and the state of dispersion was studied. As a general tendency, the nanotubes having better aqueous dispersion stability showed lower electrical percolation threshold and better nanotube dispersion in the composites. This indicates that the investigation of the stability of aqueous dispersions is also able to give information about the nanotubes inherent dispersability in polymer melts, both strongly influenced by the entanglement and agglomerate structure of the tubes within the as-produced nanotube materials. The shape of the nanotubes in the aqueous dispersions was assessed using a SYSMEX flow particle image analyzer and found to correspond to the shape observed from cryofractured surfaces of the polymer composites. © 2008 Elsevier Ltd. All rights reserved.
- ItemEffect of synthesis catalyst on structure of nitrogen-doped carbon nanotubes and electrical conductivity and electromagnetic interference shielding of their polymeric nanocomposites(New York, NY [u.a.] : Pergamon Press, 2016) Arjmand, Mohammad; Chizari, Kambiz; Krause, Beate; Pötschke, Petra; Sundararaj, UttandaramanDifferent catalysts including Co, Fe, and Ni were used to synthesize nitrogen-doped carbon nanotubes (N-CNTs) by chemical vapor deposition technique. Synthesized N-CNTs were melt mixed with a polyvinylidene fluoride (PVDF) matrix using a small scale mixer at different concentrations ranging from 0.3 to 3.5 wt%, and then compression molded. The characterization techniques revealed significant differences in the synthesis yield and the morphological and electrical properties of both N-CNTs and nanocomposites depending on the catalyst type. Whereas Co and Fe resulted in yields comparable to industrial multiwalled CNTs, Ni was much less effective. The N-CNT aspect ratio was the highest for Co catalyst, followed by Ni and Fe, whereas nitrogen content was the highest for Ni. Raman spectroscopy revealed lowest defect number and highest N-CNT crystallinity for Fe catalyst. Characterization of N-CNT/PVDF nanocomposites showed better dispersion for N-CNTs based on Co and Fe as compared to Ni, and the following order of electrical conductivity and electromagnetic interference shielding (from high to low): Co > Fe > Ni. The superior electrical properties of (N-CNT)Co nanocomposites were ascribed to a combination of high synthesis yield, high aspect ratio, low nitrogen content and high crystallinity of N-CNTs combined with a good state of N-CNT dispersion.
- ItemElectrically Conductive Polyetheretherketone Nanocomposite Filaments: From Production to Fused Deposition Modeling(Basel : MDPI, 2018-8-18) Gonçalves, Jordana; Lima, Patrícia; Krause, Beate; Pötschke, Petra; Lafont, Ugo; Gomes, José R.; Abreu, Cristiano S.; Paiva, Maria C.; Covas, José A.The present work reports the production and characterization of polyetheretherketone (PEEK) nanocomposite filaments incorporating carbon nanotubes (CNT) and graphite nanoplates (GnP), electrically conductive and suitable for fused deposition modeling (FDM) processing. The nanocomposites were manufactured by melt mixing and those presenting electrical conductivity near 10 S/m were selected for the production of filaments for FDM. The extruded filaments were characterized for mechanical and thermal conductivity, polymer crystallinity, thermal relaxation, nanoparticle dispersion, thermoelectric effect, and coefficient of friction. They presented electrical conductivity in the range of 1.5 to 13.1 S/m, as well as good mechanical performance and higher thermal conductivity compared to PEEK. The addition of GnP improved the composites' melt processability, maintained the electrical conductivity at target level, and reduced the coefficient of friction by up to 60%. Finally, three-dimensional (3D) printed test specimens were produced, showing a Young's modulus and ultimate tensile strength comparable to those of the filaments, but a lower strain at break and electrical conductivity. This was attributed to the presence of large voids in the part, revealing the need for 3D printing parameter optimization. Finally, filament production was up-scaled to kilogram scale maintaining the properties of the research-scale filaments.
- ItemHigh-Performance, Lightweight, and Flexible Thermoplastic Polyurethane Nanocomposites with Zn2+-Substituted CoFe2O4 Nanoparticles and Reduced Graphene Oxide as Shielding Materials against Electromagnetic Pollution(Washington, DC : ACS Publications, 2021-10-11) Anju; Yadav, Raghvendra Singh; Pötschke, Petra; Pionteck, Jürgen; Krause, Beate; Kuřitka, Ivo; Vilcakova, Jarmila; Skoda, David; Urbánek, Pavel; Machovsky, Michal; Masař, Milan; Urbánek, Michal; Jurca, Marek; Kalina, Lukas; Havlica, JaromirThe development of flexible, lightweight, and thin high-performance electromagnetic interference shielding materials is urgently needed for the protection of humans, the environment, and electronic devices against electromagnetic radiation. To achieve this, the spinel ferrite nanoparticles CoFe2O4 (CZ1), Co0.67Zn0.33Fe2O4 (CZ2), and Co0.33Zn0.67Fe2O4 (CZ3) were prepared by the sonochemical synthesis method. Further, these prepared spinel ferrite nanoparticles and reduced graphene oxide (rGO) were embedded in a thermoplastic polyurethane (TPU) matrix. The maximum electromagnetic interference (EMI) total shielding effectiveness (SET) values in the frequency range 8.2-12.4 GHz of these nanocomposites with a thickness of only 0.8 mm were 48.3, 61.8, and 67.8 dB for CZ1-rGO-TPU, CZ2-rGO-TPU, and CZ3-rGO-TPU, respectively. The high-performance electromagnetic interference shielding characteristics of the CZ3-rGO-TPU nanocomposite stem from dipole and interfacial polarization, conduction loss, multiple scattering, eddy current effect, natural resonance, high attenuation constant, and impedance matching. The optimized CZ3-rGO-TPU nanocomposite can be a potential candidate as a lightweight, flexible, thin, and high-performance electromagnetic interference shielding material.
- ItemEffects of synthesis catalyst and temperature on broadband dielectric properties of nitrogen-doped carbon nanotube/polyvinylidene fluoride nanocomposites(New York, NY [u.a.] : Pergamon Press, 2016) Ameli, A.; Arjmand, M.; Pötschke, Petra; Krause, Beate; Sundararaj, U.This study reports on nitrogen-doped carbon nanotube (N-CNT)/polymer nanocomposites exhibiting relatively high and frequency independent real permittivity (ϵ′) together with low dielectric loss (tan δ). N-CNTs were synthesized by chemical vapor deposition, and their nanocomposites were prepared by melt-mixing with polyvinylidene fluoride (PVDF). In the synthesis of N-CNTs, three catalysts of Co, Fe and Ni, and three temperatures of 650, 750 and 950 °C were employed. The morphology, aspect ratio, synthesis yield, remaining residue, nitrogen content, nitrogen bonding type, and powder conductivity of N-CNTs, and the morphology, polar crystalline phase, and broadband dielectric properties of N-CNT/PVDF nanocomposites were investigated. The results revealed that by proper selection of synthesis catalyst (Fe) and temperature (650 °C and 950 °C), nitrogen doping generated polarizable nanotubes via providing local polarization sites, and resulted in nanocomposites with favorable dielectric properties for charge storage applications at N-CNT loadings as low as 1.0 wt%. As a result, 3.5 wt% (N-CNT)Fe/950°C/PVDF nanocomposites exhibited an insulative behavior with ϵ' = 23.12 and tan δ = 0.05 at 1 kHz, a combination superior to that of PVDF, i.e., ϵ' = 8.4 and tan δ = 0.03 and to those of percolative nanocomposites, e.g., ϵ' = 71.20 and tan δ = 63.20 for 3.5 wt% (N-CNT)Fe/750°C/PVDF. Also, the relationships between the dielectric properties, N-CNT structure, and nanocomposite morphology were identified.
- ItemThermal conductivity of hybrid filled HDPE nanocomposites(Melville, NY : AIP, 2017) Müller, M. T.; Krause, Beate; Kretzschmar, B.; Jahn, I.; Pötschke, PetraIn this study composite materials based on high-density polyethylene (HDPE) with fillers containing nanostructures were prepared using melt mixing. Vapour Grown Carbon Fibers (VGCF), multiwalled carbon nanotubes (MWCNT) of the types Baytubes® C150P and Nanocyl™ NC7000, anthracite powder, microsilica, organoclay and expanded graphite (EG) as well as mixtures of these fillers were used. The amount and mixing ratios of the hybrid filled systems have been varied to determine their effects on the achievable level of thermal conductivity as measured on compression molded plates. The filler dispersion and phase adhesion were studied using scanning electron microscopy. When limiting the maximum filler content to 10 wt%, the highest enhancement in thermal conductivity by 166% was found for VGCF followed by a 1:1 filler combination of VGCF with EG (148%).
- ItemCellulose-carbon nanotube composite aerogels as novel thermoelectric materials(Amsterdam [u.a.] : Elsevier, 2018) Gnanaseelan, Minoj; Chen, Yian; Luo, Jinji; Krause, Beate; Pionteck, Jürgen; Pötschke, Petra; Qu, HaisongThermoelectric materials based on cellulose/carbon nanotube (CNT) nanocomposites have been developed by a facile approach and the effects of amount (2–10 wt%) and types of CNTs (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs)) on the morphology (films and aerogels) and the thermoelectric properties of the nanocomposites have been investigated. Composite films based on SWCNTs showed significantly higher electrical conductivity (5 S/cm at 10 wt%) and Seebeck coefficient (47.2 μV/K at 10 wt%) compared to those based on MWCNTs (0.9 S/cm and 11 μV/K, respectively). Lyophilization, leading to development of aerogels with sub-micron sized pores, decreased the electrical conductivity for both types by one order of magnitude, but did not affect the Seebeck coefficient of MWCNT based nanocomposites. For SWCNT containing aerogels, higher Seebeck coefficients than for films were measured at 3 and 4 wt% but significantly lower values at higher loadings. CNT addition increased the thermal conductivity from 0.06 to 0.12 W/(m∙K) in the films, whereas the lyophilization significantly reduced it towards values between 0.01 and 0.09 W/(m∙K) for the aerogels. The maximum Seebeck coefficient, power factor, and ZT observed in this study are 49 μV/K for aerogels with 3 wt% SWCNTs, 1.1 μW/(m∙K2) for composite films with 10 wt% SWCNTs, and 7.4 × 10−4 for films with 8 wt% SWCNTs, respectively.