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Schkopau, Germany

Lu K.,TU Eindhoven | Sourty E.,TU Eindhoven | Sourty E.,FEI Company | Guerra R.,Dow Chemical Company | And 2 more authors.
Macromolecules | Year: 2010

We have utilized bright field conventional transmission electron microscopy (BF-CTEM) tomography and annular dark field scanning transmission electron microscopy (ADF-STEM) tomography to characterize a well-defined carbon black (CB) filled polymer nanocomposite with known CB volume concentration. For both imaging methods, contrast can be generated between the CB and the surrounding polymer matrix. The obtained volume reconstructions were analyzed and the CB volume concentrations were carefully determined from the reconstructed data. For both imaging modes the measured CB volume concentrations are substantially different: the CB volume concentration measured in BF-CTEM tomograms exceeds by about 40%, whereas the one measured in ADF-STEM tomograms equals to a good approximation the concentration actually used to synthesize the composite. We critically discuss possible reasons for this significant difference in relation to the characteristics of the imaging technique arguing that, at least in the considered case of low electron scattering materials as polymer systems, ADF-STEM tomography provides good contrast between the components and volume data sets most suitable for further reliable quantification of nanofiller concentrations and filler distributions in polymer nanocomposite systems. © 2010 American Chemical Society.

Sladeczek F.,Dow Olefinverbund GmbH | Hottenrott K.,Martin Luther University of Halle Wittenberg
Zentralblatt fur Arbeitsmedizin, Arbeitsschutz und Ergonomie | Year: 2010

Today there is no doubt, that company based health promotion is essential for company success. At the one hand elements and actions should meet the needs of employees but on the other hand they also should have professional stress and strain in focus. But there is a danger for decreasing participation ratios in health promotion activities provided by the entrepreneur given. With this background and a strategic request of the Board of Directors of the Dow Chemical Company for measurable health improvements, it was necessary to identify new opportunities for a higher inclusion of employees, in particular of those with health risks. In cooperation with the ILUG (Institut für Leistungsdiagnostik und Gesundheitsförderung Halle) it was possible to meet this goal. The offered tests were a good opportunity for a short individual advice and for an anonymous group analysis as well.

Sijbrandi N.J.,University of Twente | Kimenai A.J.,Dow Chemical Company | Mes E.P.C.,Dow Chemical Company | Broos R.,Dow Chemical Company | And 6 more authors.
Macromolecules | Year: 2012

The synthesis, morphology, and properties of segmented poly(ether amide)s based on flexible PTHF segments (M n = 1.1 × 10 3 g mol -1) and uniform rigid oxalamide segments were investigated. The amount of oxalamide groups in the hard segment and the spacer length of bisoxalamide-based hydrogen bonded arrays were varied systematically. The segmented poly(ether amide) with single oxalamide groups connecting the polyether blocks was a sticky solid with a melting temperature of ∼25 °C. Incorporation of uniform hard segments consisting of two interconnected oxalamide units provided highly phase-separated thermoplastic elastomers with a broad temperature-independent rubber plateau. By decreasing the aliphatic spacer length separating two oxalamide units from 10 to 2 methylene groups, the melting transitions increased from 140 to 200 °C. FT-IR evidenced strongly hydrogen bonded and highly ordered bisoxalamide hard segments with degrees of ordering between 66 and 90%. AFM revealed the presence of fiber-like nanocrystals with lengths up to several hundreds of nanometers randomly dispersed in the soft PTHF matrix. The long dimension of the crystals was found parallel to the direction of the hydrogen bonds. One of the other small dimensions of the crystal approximately equals the length of the oxalamide segment, whereas the other one may correspond to the height of a stack containing ca. 10-20 hydrogen-bonded sheets. Upon heating, the crystalline phase melts over a broad temperature range to give a homogeneous melt according to temperature-dependent FT-IR, SAXS, and rheology data. Increasing the number of oxalamide groups in the hard segment to three afforded a highly phase-separated material with a melting transition above 200 °C. The segmented copolymers with two or three oxalamide groups in the hard segment show a distinct yield point and have an elastic modulus between 121 and 210 MPa, a stress at break ranging from 15 to 27 MPa, and strain at break of 150 up to 900%. The results demonstrate that alternating block copolymers with soft PTHF segments and uniform hard segments containing two or three oxalamide groups are TPEs with good thermal and mechanical properties. © 2012 American Chemical Society.

Rosenthal M.,CNRS Mulhouse Institute of Materials Science | Portale G.,European Synchrotron Radiation Facility | Burghammer M.,European Synchrotron Radiation Facility | Bar G.,Dow Olefinverbund GmbH | And 2 more authors.
Macromolecules | Year: 2012

The microstructure of banded spherulites of a typical semirigid-chain polymer, poly(trimethylene terephthalate), PTT, has been explored with microbeam X-ray diffraction. It is shown that during microbeam scans along the spherulite radius, different diffraction peaks exhibit oscillations with the same periodicity, which means that the lamellar twist is strictly uniform and regular. The twisted PTT crystals formed from the melt at 170 °C reveal a one-to-one correlation between the handedness and growth axis polarity. Thus, the lamellae are right-handed for the growth along the negative growth direction (-a) while they are left-handed for the positive growth direction (+a). This is in line with predictions of the KP-model, although the original model cannot explain why, for example left-handed crystals have to grow along (-a). The direction of the chain tilt in the lamellar crystal correlates with the lamellar handedness as postulated by the KP-model. However, the measured chain tilt in the crystal (4°) is too faint to be the primary source of the surface stresses required for twisted lamellar growth. © 2012 American Chemical Society.

Rosenthal M.,CNRS Mulhouse Institute of Materials Science | Bar G.,Dow Olefinverbund GmbH | Burghammer M.,European Synchrotron Radiation Facility | Ivanov D.A.,CNRS Mulhouse Institute of Materials Science
Angewandte Chemie - International Edition | Year: 2011

Twisted crystals: Upon crystallization, achiral polymers can form chiral crystalline lamellae, such as right- and left-handed helicoids. The chiral parameter imparted by crystallization is the chain tilt with respect to the lamellar normal. Thus, lamella having crystalline stems tilted to the right from the normal to the basal plane will form right-handed helicoids, and vice versa. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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