20 results
Search Results
Now showing 1 - 10 of 20
- ItemMelt-mixed PP/MWCNT composites: Influence of CNT incorporation strategy and matrix viscosity on filler dispersion and electrical resistivity(Basel : MDPI, 2019) Pötschke, Petra; Mothes, Fanny; Krause, Beate; Voit, BrigitteSmall-scale melt mixing was performed for composites based on polypropylene (PP) and 0.5–7.5 wt % multiwalled carbon nanotubes (MWCNT) to determine if masterbatch (MB) dilution is a more effective form of nanofiller dispersion than direct nanotube incorporation. The methods were compared using composites of five different PP types, each filled with 2 wt % MWCNTs. After the determination of the specific mechanical energy (SME) input in the MB dilution process, the direct-incorporation mixing time was adjusted to achieve comparable SME values. Interestingly, the electrical resistivity of MB-prepared samples with 2 wt % MWCNTs was higher than that of those prepared using direct incorporation—despite their better dispersion—suggesting more pronounced MWCNT shortening in the two-step procedure. In summary, this study on PP suggests that the masterbatch approach is suitable for the dispersion of MWCNTs and holds advantages in nanotube dispersion, albeit at the cost of slightly increased electrical resistivity.
- 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.
- ItemThe influence of the blend ratio in PA6/PA66/MWCNT blend composites on the electrical and thermal properties(Basel : MDPI, 2019) Krause, Beate; Kroschwald, Lisa; Pötschke, PetraIt is known that the percolation threshold of polyamide 6 (PA6)/multiwalled carbon nanotube (MWCNT) composites is higher than that of PA66/MWCNT composites under the same mixing conditions and melt viscosity. A series of blends of PA6 and PA66 containing 1 wt % MWCNTs have been prepared to investigate this phenomenon. At contents up to 20 wt % PA66, the blends were not electrically conductive. The electrical resistivity dropped to 109 Ohm∙cm for PA66/PA6 30/70 blends. The resistivity was 105 Ohm∙cm at higher PA66 contents. Differential scanning calorimetry was used to investigate the thermal behavior of blends. The glass transition temperature was almost constant for all blend compositions, indicating that the amorphous phases are miscible. The MWCNT addition influenced the crystallization of PA66 much more than the PA6 crystallization. A heterogeneous crystallization of the polyamide in PA66/PA6 blends took place, and the MWCNTs were mainly localized in the earlier crystallizing PA66 phase. Thus, the formation of the nanotube network and thus the electrical volume resistivity of the PA6/PA66 blends with 1 wt % MWCNTs is significantly influenced by the crystallization behavior. In PA66/PA6 blends up to 60 wt %, the more expensive PA66 can be replaced by the cheaper PA6 while retaining its electrical properties
- ItemSystematic evaluation of oligodeoxynucleotide binding and hybridization to modified multi-walled carbon nanotubes(London : Biomed Central, 2017) Kaufmann, Anika; Hampel, Silke; Rieger, Christiane; Kunhardt, David; Schendel, Darja; Füssel, Susanne; Schwenzer, Bernd; Erdmann, KatiBackground: In addition to conventional chemotherapeutics, nucleic acid-based therapeutics like antisense oligodeoxynucleotides (AS-ODN) represent a novel approach for the treatment of bladder cancer (BCa). An efficient delivery of AS-ODN to the urothelium and then into cancer cells might be achieved by the local application of multi-walled carbon nanotubes (MWCNT). In the present study, pristine MWCNT and MWCNT functionalized with hydrophilic moieties were synthesized and then investigated regarding their physicochemical characteristics, dispersibility, biocompatibility, cellular uptake and mucoadhesive properties. Finally, their binding capacity for AS-ODN via hybridization to carrier strand oligodeoxynucleotides (CS-ODN), which were either non-covalently adsorbed or covalently bound to the different MWCNT types, was evaluated. Results: Pristine MWCNT were successfully functionalized with hydrophilic moieties (MWCNT-OH, -COOH, -NH2, -SH), which led to an improved dispersibility and an enhanced dispersion stability. A viability assay revealed that MWCNT-OH, MWCNT-NH2 and MWCNT-SH were most biocompatible. All MWCNT were internalized by BCa cells, whereupon the highest uptake was observed for MWCNT-OH with 40% of the cells showing an engulfment. Furthermore, all types of MWCNT could adhere to the urothelium of explanted mouse bladders, but the amount of the covered urothelial area was with 2-7% rather low. As indicated by fluorescence measurements, it was possible to attach CS-ODN by adsorption and covalent binding to functionalized MWCNT. Adsorption of CS-ODN to pristine MWCNT, MWCNT-COOH and MWCNT-NH2 as well as covalent coupling to MWCNT-NH2 and MWCNT-SH resulted in the best binding capacity and stability. Subsequently, therapeutic AS-ODN could be hybridized to and reversibly released from the CS-ODN coupled via both strategies to the functionalized MWCNT. The release of AS-ODN at experimental conditions (80 °C, buffer) was most effective from CS-ODN adsorbed to MWCNT-OH and MWCNT-NH2 as well as from CS-ODN covalently attached to MWCNT-COOH, MWCNT-NH2 and MWCNT-SH. Furthermore, we could exemplarily demonstrate that AS-ODN could be released following hybridization to CS-ODN adsorbed to MWCNT-OH at physiological settings (37 °C, urine). Conclusions: In conclusion, functionalized MWCNT might be used as nanotransporters in antisense therapy for the local treatment of BCa.
- ItemNanofiller dispersion, morphology, mechanical behavior, and electrical properties of nanostructured styrene-butadiene-based triblock copolymer/CNT composites(Basel : MDPI, 2019) Staudinger, Ulrike; Satapathy, Bhabani K.; Jehnichen, DieterA nanostructured linear triblock copolymer based on styrene and butadiene with lamellar morphology is filled with multiwalled carbon nanotubes (MWCNTs) of up to 1 wt% by melt compounding. This study deals with the dispersability of the MWCNTs within the nanostructured matrix and its consequent impact on block copolymer (BCP) morphology, deformation behavior, and the electrical conductivity of composites. By adjusting the processing parameters during melt mixing, the dispersion of the MWCNTs within the BCP matrix are optimized. In this study, the morphology and glass transition temperatures (Tg) of the hard and soft phase are not significantly influenced by the incorporation of MWCNTs. However, processing-induced orientation effects of the BCP structure are reduced by the addition of MWCNT accompanied by a decrease in lamella size. The stress-strain behavior of the triblock copolymer/MWCNT composites indicate higher Young’s modulus and pronounced yield point while retaining high ductility (strain at break ~ 400%). At a MWCNT content of 1 wt%, the nanocomposites are electrically conductive, exhibiting a volume resistivity below 3 × 103 Ω·cm. Accordingly, the study offers approaches for the development of mechanically flexible functional materials while maintaining a remarkable structural property profile.
- 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.
- 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.
- ItemDispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions(Oxford : Elsevier Science, 2014) Staudinger, Ulrike; Krause, Beate; Steinbach, Christine; Pötschke, Petra; Voit, BrigitteThe dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloroform and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions.
- ItemNanocomposites with p-and n-type conductivity controlled by type and content of nanotubes in thermosets for thermoelectric applications(Basel : MDPI, 2020) Kröning, Katharina; Krause, Beate; Pötschke, Petra; Fiedler, BodoIn this work, composites based on epoxy resin and various carbon nanotubes (CNTs) were studied regarding their thermoelectric properties. The epoxy composites were prepared by infiltration of preformed CNT buckypapers. The influence of different types of CNTs on the Seebeck coefficient was investigated, namely lab-made and commercially available multi walled carbon nanotubes (MWCNTs), lab-made nitrogen doped MWCNTs (N-MWCNT) and commercially available single walled carbon nanotubes (SWCNTs). It was found that only by varying the lab-made MWCNT content could both n-and p-type composites be produced with Seebeck coefficients between -9.5 and 3.1 µV/K. The incorporation of N-MWCNTs resulted in negative Seebeck coefficients of -11.4 to -17.4 µV/K. Thus, the Seebeck coefficient of pure SWCNT changed from 37.4 to -25.5 µV/K in the epoxy/1 wt. % SWCNT composite. A possible explanation for the shift in the Seebeck coefficient is the change of the CNTs Fermi level depending on the number of epoxy molecules on the CNT surface. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemThe influence of matrix viscosity on MWCNT dispersion and electrical properties in different thermoplastic nanocomposites(Oxford : Elsevier Science, 2012) Socher, Robert; Krause, Beate; Müller, Michael T.; Boldt, Regine; Pötschke, PetraComposites of MWCNTs having each three different levels of matrix viscosity with five different polymers (polyamide 12, polybutylene terephthalate, polycarbonate, polyetheretherketone and low density polyethylene) were melt mixed to identify the general influence of matrix viscosity on the electrical properties and the state of MWCNT dispersion. Huge differences in the electrical percolation thresholds were found using the same polymer matrix with different viscosity grades. The lowest percolation thresholds were always found in the composites based on the low viscosity matrix. The state of primary MWCNT agglomerate dispersion increased with increasing matrix viscosity due to the higher input of mixing energy. TEM investigations showed nanoagglomerated structures in the low viscosity samples which are obviously needed to achieve low resistivity values. The effect of nanotube shortening was quantified using two different viscosity grades of polycarbonate. Due to the higher mixing energy input the nanotube shortening was more pronounced in the high viscosity matrix which partially explains the higher percolation threshold. © 2011 Elsevier Ltd. All rights reserved.