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Author: Krause, Beate × End date: 2009 × Start date: 2006 ×

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    Comparison of the molecular properties and morphology of polypropylenes irradiated under different atmospheres and after annealing
    (Hoboken, NJ [u.a.] : Wiley InterScience, 2006) Krause, Beate; Häußler, Liane; Voigt, Dieter
    Electron-beam irradiation, a well-known way of generating long-chain branching, was used to modify polypropylene. Samples were investigated with differential scanning calorimetry, polarized light microscopy, and size exclusion chromatography. Independently of the atmosphere, postannealing led to the deactivation of residual radicals and to the reduction of the nucleus density. In comparison with the initial polypropylene, the crystallization temperatures increased for nonannealed samples but decreased for annealed samples. Stable products were obtained only by irradiation in nitrogen followed by annealing. A reaction including free radicals with oxygen in the ambient atmosphere led to increasing molar mass degradation and the formation of long-chain branching after Storage. © 2006 Wiley Periodicals, Inc.
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    Correlation 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, Petra
    In 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.
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    Characterization of electron beam irradiated polypropylene: Influence of irradiation temperature on molecular and rheological properties
    (Hoboken, NJ [u.a.] : Wiley InterScience, 2006) Krause, Beate; Voigt, Dieter; Häuβler, Liane; Auhl, Dietmar; Münstedt, Helmut
    The aim of the investigations was to analyze the influence of the temperature during the irradiation process of polypropylene on the molar mass, the formation of long chain branching and the final branching topology. A linear isotactic polypropylene homopolymer was modified by electron beam irradiation at different temperatures, with two irradiation doses to insert long chain branching. The Samples were analyzed by size exclusion chromatography coupled with a multiangle laser light scattering detector, by differential scanning calorimetry, and by shear and elongational rheology. The shear and elongational flow behavior isdiscussed in terms of the influence of molecular parameters and used to analyze the topology of the irradiated samples. With increasing temperature, a slight reduction of the molar mass, an increase of long chain branching and an increase of crystallization temperature were found. © 2006 Wiley Periodicals, Inc.
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    Long-chain branching of polypropylene by electron-beam irradiation in the molten state
    (Hoboken, NJ [u.a.] : Wiley InterScience, 2006) Krause, Beate; Stephan, M.; Volkland, S.; Voigt, D.; Häußler, L.; Dorschner, H.
    The electron-beam irradiation of polymers generates modification effects in the macromolecular structure and material properties. Therefore, irradiation processing is mostly realized in the polymer solid state. In this way, the modification of linear polypropylene may result in long-chain branching of polypropylene macromolecules. The objective of this article is to investigate the effect of a polymer in the molten state during electron-beam irradiation on the macromolecular structure and material properties of polypropylene. For this procedure, a special irradiation vessel (BG3) has been developed in which a rapid transfer of polymer films from the solid state to the molten state and a defined temperature during electron-beam irradiation are realizable. The irradiated samples have been analyzed by high-temperature size exclusion chromatography coupled with a multi-angle laser light scattering detector and differential scanning calorimetry (DSC) measurements. With an increasing irradiation dose, a high reduction of the molar mass and an increasing amount of long-chain branching are found. Compared with irradiation in the solid state, the modification in the molten state leads to a higher degree of branching. The Theological experiments in elongation flow clearly exhibit the existence of long-chain branching. Furthermore, DSC measurements show that the glass-transition temperature and peak temperatures of melting and crystallization decrease. © 2005 Wiley Periodicals, Inc.
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    Influence of small scale melt mixing conditions on electrical resistivity of carbon nanotube-polyamide composites
    (Barking : Elsevier, 2009) Krause, Beate; Pötschke, Petra; Häußler, Liane
    Polyamide 6 (PA6) and polyamide 6.6 (PA66) were filled with multiwalled carbon nanotubes (MWNT) using small scale melt mixing under variation of processing conditions, including temperature, rotation speed, and mixing time. In PA66 an electrical percolation threshold of 1 wt% MWNT was found which is lower than that of PA6 at 2.5-4 wt%. In both cases mixing conditions influenced strongly the dispersion and distribution of CNT and the electrical volume resistivity, whereas crystallisation behaviour was only slightly changed. With increasing mixing energy input remaining agglomerates were less in number and smaller, leading to better dispersion. On the other hand, in samples containing 5 wt% MWNT in PA6 electrical volume resistivity showed a minimum at a quite low energy input and then increased considerably with further input of mixing energy. This increase may be related to MWNT breaking during mixing and encapsulation of MWNT by the polyamide chains. © 2008 Elsevier Ltd. All rights reserved.