Showing papers by "Dipak Khastgir published in 1991"

Electromagnetic Interference Shielding by Conductive Nitrile Rubber Composites Containing Carbon Fillers

Abstract: Electromagnetic interference (EMI) shielding characteristics of nitrile rubber composites filled with short-carbon fibre (SCF), conductive car bon black (Conductex™ 900), and filler blend (SCF + Co...

The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubber

Abstract: The effect of carbon black concentration on the dynamic mechanical properties of bromobutyl rubber vulcanizates has been studied over a wide range of temperature (− 150 to + 250 °C), frequency (3.5 to 110 Hz) and dynamic strain amplitude (0.07 to 5%). The influence of carbon black concentration on the glass-rubber transition has also been investigated with respect to the isochronal variation in dynamic properties. The influence of carbon black concentration consists mainly of the change in the levels of the moduli values in the glassy and rubbery state. In the glassy region; the increase in stiffness with carbon black loading may be fully explained by the hydrodynamic effect of the carbon black particles embedded in the polymer continuum. With increased carbon black concentration the glass-rubber transition temperature (tan δ peak temperature) does not show a shift in its location but peak shoulder broadening and decrease in peak height are observed. At a particular temperature, the effect of carbon black concentration on dynamic properties of bromobutyl rubber is dependent on the combined effects of applied strain amplitude and frequency. With increase in filler concentration the thermal stability of the vulcanizate increases.

Effect of frequency and temperature on dielectric properties of polystyrene at microwave frequencies

Abstract: Ambient dielectric measurements as functions of frequency in X-band microwave region have been made on solid samples of polystyrene. Effects of temperature (−120 to +160°C) at three different frequencies have also been studied. The measurement technique applied based on short-circuited waveguide method of Roberts and von Hippel modified by Dakin and Works for low loss and medium loss samples. Two different types of relaxations are identified originating from main chain motion, wagging, and rotational motions of pendent phenyl group. Intrinsic activation energy for polystyrene molecule, dipole moment per repeat unit, and the average apparent energy of a polystyrene molecule associated with its induced transient dipoles have also been calculated and the data so obtained are explained and compared with standard literature. Die dielektrischen Eigenschaften von Polystyrol wurden zwischen –120 und +160°C bei drei Frequenzen im Mikrowellenbereich untersucht. Die Mestechnik basierte auf der von Dakin und Works modifizierten Kurzschluswellenleiter-Methode nach Roberts und von Hippel fur Material mit niedrigen und mittleren Verlustmoduli. Zwei verschiedene Relaxationsmechanismen wurden identifiziert, die von der Hauptkettenbewegung und den Rotationsschwingungen der Phenylringe herruhren. Aktivierungsenergien und Dipolmomente wurden berechnet, interpretiert und mit Literaturwerten verglichen.