Browsing by Author "Kobashi, Kazufumi"

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    Liquid 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, Petra
    Liquid 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.
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    Liquid sensing properties of fibres prepared by melt spinning from poly(lactic acid) containing multi-walled carbon nanotubes
    (Amsterdam [u.a.] : Elsevier, 2010) Pötschke, Petra; Andres, Timo; Villmow, Tobias; Pegel, Sven; Brünig, Harald; Kobashi, Kazufumi; Fischer, Dieter; Häussler, Liane
    Poly(lactic acid) (PLA)/multi-walled carbon nanotube (MWNT) composites were melt spun with different take-up velocities (max. 100 m/min) to obtain electrically conductive fibres. The incorporation of MWNT contents between 0.5 and 5.0 wt.% was realised in a previous melt mixing process using twin-screw extrusion. The relative resistance change of the fibres caused by contact with different solvents (water, n-hexane, ethanol, methanol) and solvent concentrations was used as liquid sensing response, whereas the time dependent resistance was recorded during immersion and drying cycles. Transmission electron microscopy and Raman spectroscopy indicated enhanced orientation of MWNT along the fibre axis with take-up velocity, resulting in decreased sensitivity during solvent contact. Additionally, sensitivity decreased as the weight content of MWNT increased and was furthermore dependent on the characteristics of used solvents. In context with the targeted application of leakage detection, fibres with low MWNT amount and low draw down ratio (as extruded fibres with 2 wt.% MWNT) are suitable, as they showed relative resistance changes of up to 87% after 10 min immersion in methanol even if the recovery upon drying was suppressed significantly.
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    Liquid sensing properties of melt processed polypropylene/poly(ε-caprolactone) blends containing multiwalled carbon nanotubes
    (Amsterdam [u.a.] : Elsevier, 2011) Pötschke, Petra; Kobashi, Kazufumi; Villmow, Tobias; Andres, Timo; Paiva, Maria Conceição; Covas, José António
    The sensing properties of polypropylene (PP)/poly(ε-caprolactone) (PCL) blends containing multiwalled carbon nanotubes (MWNT) were studied in terms of their electrical resistance change in presence of liquids (solvents). The preparation of co-continuous blends based on the double percolation concept was done by melt mixing of electrically conductive PCL composites containing 3. wt.% MWNT and neat PP in ratios of 30:70, 40:60, and 50:50. The electrical resistance change of the PCL-MWNT composites and blends was monitored in a solvent immersion/drying cycle. Various solvents, such as n-hexane, ethanol, methanol, water, toluene, chloroform, and tetrahydrofuran were successfully detected, yielding different responses and reversibility of the resistance changes.PP and PCL were tested separately for solvent sorption using ethanol and n-hexane, both showing a low sorption of n-hexane. Ethanol sorption was large for PCL and almost absent for PP. The 50/50 blend composites with 3. wt.% MWNT in the PCL phase presented larger resistance changes for n-hexane, showing larger sensing ability for this solvent compared to PCL composites with 1 and 3. wt.% loadings. The opposite response was observed for immersion in ethanol where the PCL-MWNT composites showed larger changes than the blends. As the ratio of the conductive PCL phase over PP in the blend composition (i.e. the overall MWNT content) decreased, larger resistance changes were observed. The liquid sensing properties of compression-moulded discs and melt-drawn filaments were compared indicating higher responses for the discs.