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- ItemMultifilament fibres of poly(ε-caprolactone)/poly(lactic acid) blends with multiwalled carbon nanotubes as sensor materials for ethyl acetate and acetone(Amsterdam [u.a.] : Elsevier, 2011) Rentenberger, Rosina; Cayla, Aurélie; Villmow, Tobias; Jehnichen, Dieter; Campagne, Christine; Rochery, Maryline; Devaux, Eric; Pötschke, PetraConductive poly(ε-caprolactone) (PCL) + 4% multiwalled carbon nanotubes (MWCNTs)/poly(lactic acid) (PLA) = 50/50 wt% blend multifilament fibres were melt-spun and a woven textile was made by a handloom with the conductive fibres in weft direction. The fibres were tested for cyclic liquid sensing in ethyl acetate and acetone as two moderate solvents and in ethanol as a poor solvent. The liquid sensing responses, namely the relative resistance changes Rrel relating the resistance change to the initial resistance of the samples on contact with ethyl acetate and acetone, were fast (R rel higher than 16 after 100 s), with high amplitudes (R rel higher than 23 after 500 s), and well reproducible. At the same time, the fibres were resistant against these solvents. The response to ethanol was also reproducible, however, very slow and with low amplitude. PLA was found to crystallize during the immersion process, whereas in PCL the crystalline domains transformed into amorphous ones as studied by Wide Angle X-ray Diffraction. The crystallization of PLA does not influence negatively the liquid sensing properties which can be assigned to the finding that the MWCNT are predominantly localized in the PCL phase as confirmed by Scanning Electron Microscopy. In the final step, a textile based on those fibres was prepared and its sensing behaviour was investigated on ethyl acetate and acetone clearly showing that such textiles are suitable to detect these solvents.
- ItemVapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks(Amsterdam [u.a.] : Elsevier, 2011) Fan, Qingqing; Qin, Zongyi; Villmow, Tobias; Pionteck, Jürgen; Pötschke, Petra; Wu, Yongtao; Voit, Brigitte; Zhu, MeifangThe volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament - carbon nanotubes (TPU-CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU-CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU-CNTs composite, while the former effect plays the major role.
- ItemDuctile-to-semiductile transition in PP-MWNT nanocomposites(Weinheim : Wiley-VCH, 2007) Satapathy, Bhabani K.; Ganß, Martin; Weidisch, Roland; Pötschke, Petra; Jehnichen, Dieter; Keller, Thomas; Jandt, Klaus D.A ductile-to-semiductile transition in the crack resistance behaviour of PP/MWNT composites is discussed, using an essential work of fracture approach based on a post yield fracture mechanics concept and its possible interrelation to the structural attributes studied by TEM, SEM, and WAXD. A maximum in the non-essential work of fracture is observed at 0.5 wt-% MWNT content, which demonstrates the enhanced resistance to crack propagation compared to pure PP, followed by a sharp decline with the increase in MWNT content to 1.5 wt.-%, which reveals a ductile-to-semiductile transition. Fracture kinetic studies present a qualitative picture of the nature of such a transition in terms of a) switch over from non-steady (in pure PP) to steady-state crack tip opening displacement rate (in nanocomposites), and b) a ductile-to-semiductile transition
- ItemAttenuation of electromagnetic waves by carbon nanotube composites(Amsterdam [u.a.] : Elsevier, 2008) Hornbostel, Björn; Leute, Ulrich; Pötschke, Petra; Kotz, Jochen; Kornfeld, Daniela; Chiu, Po-Wen; Roth, SiegmarExperiments on polycarbonate/single-walled carbon nanotube composites were performed to explore the potential of carbon nanotubes in attenuating electromagnetic waves. According to the results of these experiments a distinct effect is present. The effect is dependent on the tubular filler properties and on the morphology of the composite. At a loading of 5.4 wt% single-walled carbon nanotubes in polycarbonate an attenuation of the field of 47 dB could be detected, which corresponds an attenuation of the power of 99.998%.
- ItemLiquid sensing of melt-processed poly(lactic acid)/multi-walled carbon nanotube composite films(Amsterdam [u.a.] : Elsevier, 2008) Kobashi, Kazufumi; Villmow, Tobias; Andres, Timo; Pötschke, PetraLiquid sensing properties of poly(lactic acid) (PLA)/multi-walled carbon nanotube (MWNT) composites were studied on the basis of the change of electrical properties on solvent contact. The composites were prepared by melt processing using a twin screw extruder. The MWNT loading differed between 0.5 and 2.0 wt%, and an electrical percolation threshold below 0.5 wt% MWNT content was obtained. TEM observations revealed that the nanotubes form a conductive network structure in the PLA matrix, which is the key for liquid sensing. Electrical resistance of the composites was monitored in solvent immersion/drying cycles on samples prepared from thin pressed composite sheets. The resistance reversibly changed upon the cycles with good reproducibility. Lower MWNT loadings resulted in larger resistance changes, indicating that the conductive MWNT network tends to readily disconnect due to the less dense structures as compared to higher loadings. Various solvents (n-hexane, toluene, chloroform, tetrahydrofuran, dichloromethane, ethanol, and water) were successfully detected, showing different degrees of the resistance changes (ca. 4-1.0 × 103 Ω) and the relative resistance changes (ca. 0.003-3.0 × 103). The solubility parameters of the solvents were found to be good indicators to estimate liquid sensing properties of these PLA/MWNT composites for the poor and good solvents.
- ItemFire behaviour of polyamide 6/multiwall carbon nanotube nanocomposites(New York, NY [u.a.] : Elsevier, 2005) Schartel, B.; Pötschke, Petra; Knoll, U.; Abdel-Goad, M.Nanocomposites of polyamide 6 with 5 wt.% multiwall carbon nanotubes are investigated to clarify their potential as regards the fire retardancy of polymers. The nanocomposites are investigated using SEM, electrical resistivity, and oscillatory shear rheology. The pyrolysis is characterized using thermal analysis. The fire behaviour is investigated with a cone calorimeter using different external heat fluxes, by means of the limiting oxygen index and the UL 94 classification. The fire residue is characterized using SEM. The comprehensive fire behaviour characterization not only allows the materials' potential for implementation in different fire scenarios and fire tests to be assessed, but also provides detailed insight into the active mechanisms. The increased melt viscosity of the nanocomposites and the fibre-network character of the nanofiller are the dominant mechanisms influencing fire performance. The changes are found to be adjuvant with respect to forced flaming conditions in the cone calorimeter, but also deleterious in terms of flammability.
- ItemRheological characterization of melt processed polycarbonate-multiwalled carbon nanotube composites(Amsterdam : Elsevier, 2005) Abdel-Goad, Mahmoud; Pötschke, PetraIn this study polycarbonate/multiwalled carbon nanotube composites were produced with different compositions by diluting a masterbatch using melt mixing in a DACA-Micro-Compounder. The composites were rheologically characterized using an ARES-rheometer in the dynamic mode under nitrogen atmosphere at 280 °C and frequency varying from 100 to 0.056 rad/s. The results showed that the dynamic moduli and the viscosity increased with increasing MWNT content. At a concentration of 0.5 wt.% MWNT, a significant change in the frequency dependence of the moduli was observed which indicates a transition from a liquid like to a solid like behavior of the nanocomposites. This transition can be related to the formation of a combined network between the nanotubes and the polymer chains.
- ItemMelt mixing of polycarbonate with multiwalled carbon nanotubes: Microscopic studies on the state of dispersion(New York, NY [u.a.] : Elsevier, 2004) Pötschke, Petra; Bhattacharyya, Arup R.; Janke, AndreasThe focus of the paper is to investigate several issues related to the state of dispersion of multiwalled carbon nanotubes (MWNTs) in a polycarbonate (PC) matrix. A masterbatch of PC-MWNT (15 wt.%) was diluted with different amounts of PC in a small scale conical twin screw extruder (DACA Micro Compounder) to obtain different compositions of MWNT. In this system, electrical measurements indicated percolation of MWNT between 1.0 and 1.5 wt.%. We report TEM and AFM investigations of the state of dispersion of MWNT, in the entire volume of the matrix, in selected composites with compositions below (1 wt.% MWNT) and above the percolation threshold (2 and 5 wt.% MWNT). In addition, it was investigated if surface segregation of MWNT and flow induced orientation of nanotubes within the extruded strands had been occurred. It is found that the nanotubes dispersed uniformly through the matrix showing no significant agglomeration in the compositions studied. TEM micrographs seem to be able to detect the percolated structure of the carbon nanotubes. Furthermore, by comparing AFM micrographs from the core region and near to surface region no evidence of segregation or depletion of MWNT at the surface of the extruded strand was found. Comparison of TEM and AFM micrographs on surfaces cut along and perpendicular to the strand direction led to the conclusion that no preferred alignment had occurred as a result of extrusion. Aside from TEM technique, AFM is shown to be suitable to characterize the state of nanotube dispersion along with the issue of surface segregation and orientation of the nanotubes.
- ItemElectrical, rheological and morphological studies in co-continuous blends of polyamide 6 and acrylonitrile-butadiene-styrene with multiwall carbon nanotubes prepared by melt blending(Amsterdam [u.a.] : Elsevier, 2009) Bose, Suryasarathi; Bhattacharyya, Arup R.; Kulkarni, Ajit R.; Pötschke, PetraMultiwall carbon nanotubes (MWNT) were incorporated in melt-mixed co-continuous blends of polyamide 6 (PA6) and acrylonitrile-butadiene-styrene (ABS) using a conical twin-screw microcompounder. The state of dispersion of MWNT in the blends was assessed through AC electrical conductivity measurements and melt-rheological investigations. The electrical and rheological percolation threshold in PA6/ABS blends was ∼3-4 and ∼1-2 wt% MWNT, respectively. A unique reactive modifier (sodium salt of 6-amino hexanoic acid, Na-AHA) was employed to facilitate 'network-like' structure of MWNT and to confine them in a specific phase. This was achieved by establishing specific interactions with the delocalized 'π-electron' clouds of MWNT and melt-interfacial reaction during melt-mixing. The electrical percolation threshold was significantly reduced in the blends (∼0.25 wt%) in the presence of Na-AHA modified MWNT and even coincided with the rheological percolation threshold. Significant refinement in the co-continuous structure was also observed in the presence of Na-AHA modified MWNT.
- ItemUse of carbon nanotube filled polycarbonate in blends with montmorillonite filled polypropylene(Amsterdam [u.a.] : Elsevier, 2007) Pötschke, Petra; Kretzschmar, Bernd; Janke, AndreasBlends were prepared by melt mixing from a conductive polycarbonate composite filled with multiwalled carbon nanotubes (MWNT) and polypropylene containing clay (montmorillonite, MMT). The PC composite, containing 2 wt% MWNT (PC-2NT), was prepared by diluting a PC masterbatch by melt extrusion. The PP nanoclay composite with 3 wt% MMT (PP-3MMT) was produced by melt compounding. Blends were prepared in a small scale Daca Microcompounder over the whole composition range. The aim of the study was to produce conductive blends containing less MWNT than required for the pure PC by using the concept of double percolation through the formation of a co-continuous morphology. The fully co-continuous morphology range was found between 40 and 80 wt% of the filled PC phase. A significant increase in electrical conductivity could be obtained in the composition range starting at 50 wt% (MWNT content about 0.6 vol%). In this range the filled PC forms a continuous phase. Whereas in the blends the MWNT were still dispersed homogeneously within the PC phase, the MMT segregated from the PP towards the blend interface.