Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite's electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred

Modelling of Pore Collapse during Polymer Sintering: Viscoelastic Model with Enclosed Gas

Frenkel’s model for the late stage of coalescence of viscous particles has been extended to describe pore collapse in a viscoelastic melt during polymer sintering. The shrinkage of a pore in a polymer melt driven by surface tension is extended by taking into account the effects of trapped gas and gas transport out of the pore. Viscoelasticity has been shown to have a considerable impact on the time scale of the coalescence process. In addition, gas diffusion modifies the coalescence dynamics. Based on a parameter study, different regimes for the pore collapse have been identified. At the beginning of pore collapse, surface tension is considerably stronger than gas pressure within the pore. In this time interval (surface-tension-driven regime), the pore shrinks even in the absence of gas diffusion through the matrix. In the absence of gas transport, the shrinkage dynamic slows down and stops when the surface tension balances the gas pressure in the pore. If gas transport out of the pore is possible, surface tension and gas pressure are balanced while the gas pressure slowly decreases (diffusion-controlled regime). The final phase of pore collapse, which occurs when the gas pressure within the pore decreases sufficiently, is controlled again by surface tension. The limitations of the model are discussed. To analyze the interplay between different mechanisms and process steps during selective laser sintering, the respective time scales are compared using experimental data

Thermische Alterung und Eigenschaften von Polymermaterialien für das selektive Lasersintern

Die thermische Alterung von Polyamid-12-Pulvern für das Selektive Lasersintern bzw. gesinterte Prüfkörpern unter Stickstoff und in Luft wurde mit Differenzkalorimetrie, dynamisch-mechanischer Analyse, Lichtmikroskopie und Bildanalyse, Schlagzähigkeitsexperimenten, rheologischen Messungen in der Schmelze sowie mit GPC und Infrarot-Spektroskopie sowie thermogravimetrischer Analyse untersucht. Die mittlere Molmasse nimmt mit zunehmender Alterungszeit und steigenden Alterungstemperaturen zu. Zeitaufgelöste rheologische Messungen in der Schmelze zeigen eine Zunahme der Molmasse und/oder das Entstehen von Vernetzungen. Für längere Alterungszeiten bei höheren Temperaturen ist ein Kettenabbau nachweisbar. Als Alterungsmechanismus wird ein Wechselspiel von Kettenverlängerung/Vernetzung und thermo-oxidativem Abbau angenommen

Stochastic temperature modulation : a new technique in temperature-modulated DSC

A new temperature-modulated differential scanning calorimetry (TMDSC) technique is introduced. The technique is based on stochastic temperature modulation and has been developed as a consequence of a generalized theory of a temperature-modulated DSC. The quasi-static heat capacity and the frequency-dependent complex heat capacity can be determined over a wide frequency range in one single measurement without further calibration. Furthermore, the reversing and non-reversing heat flows are determined directly from the measured data. Examples show the frequency dependence of the glass transition, the isothermal curing of thermosets and a solid–solid transition

Down-to-earth coatings: Carbon nanotube paints reduce lightning damage to aircraft

The low conductivity of composite materials used on aircraft, wind turbines etc. can lead to damage by lightning strikes, and conventional paints can aggravate this problem. Carbon nanotubes offer the possibility of producing paints with special electrical properties for this application as well as for electronics use. Studies now being undertaken are outlined and some initial results are presented

Effect of Irradiation Temperature and Atmosphere on Aging of Epoxy Resins for Superconducting Magnets

The superconducting magnets of future particle accelerators will be exposed to high irradiation doses at cryogenic temperatures. To investigate the effect of irradiation temperature and atmosphere on the aging behavior, we have characterized the changes in thermomechanical properties of six epoxy resins for potential use in superconducting magnets after irradiation up to 20 MGy in ambient air, inert gas, and liquid helium. Based on the results obtained by Dynamic Mechanical Analysis (DMA), we discuss the effect of irradiation temperature and the presence of oxygen. The irradiation temperature can have a strong influence on the rates at which cross-linking and chain scission occur