Paulus Antonius Maria Steeman

Dielectric properties of polyamide-4,6

Abstract The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature and moisture content. The dielectric spectra were compared with the results of dynamic mechanical measurements in torsion at 0.2153 Hz, as a function of temperature, and with the dynamic dielectric properties of commercial polyamide-6,6. Three relaxation processes are observed in polyamide-4,6, which are related to either local or collective molecular mechanisms of motion, similar to the relaxation processes observed in other polyamides. At temperatures above the glass transition temperature, ionic conductivity is observed, which, due to the semicrystalline structure of the material, gives rise to a strong Maxwell—Wagner—Sillars (MWS) polarization. With increasing temperature, the conductivity increases sharply, eventually causing electrode polarization, and thus obscuring the dielectric effects in the material. All loss processes shift to lower temperatures with increasing water content. The activation energies of the secondary relaxations decrease with increasing water uptake, while the β and α relaxations are enhanced in magnitude.

Micromechanical and microdielectric transitions in P(S-g-EO) modified PPO/PMMA blends

Abstract The effect of two poly(styrene- graft -ethylene oxide)s with different graft lengths and graft densities on the interphase properties of poly(2,6-dimethyl-1,4-phenylene oxide)/poly(methyl methacrylate) (PPO/PMMA) blends was studied by different techniques. The miscibility between the copolymers and the homopolymers, as well as the phase reduction in the ternary blends, was favoured by longer and more separated grafts. Transmission electron microscopy shows that the addition of any of the copolymers leads to the formation of an interphase between the heterogeneous PPO and PMMA phases. The ternary blends present micromechanical and microdielectric transitions at temperatures in the range 60–100°C, where the transition temperatures decrease with increasing copolymer contents. The micromechanical and microdielectric transitions originate from the change in the relative moduli values and the dielectric losses of the matrix, interphase and particle phase of the ternary blends.

Dielectric monitoring of water absorption in glass-bead-filled high-density polyethylene

Abstract Model composites of spherical glass particles dispersed in a matrix of high-density polyethylene (HDPE) were prepared. Samples of the composite material were, after careful drying, exposed to several relative humidities at room temperature. The dielectric properties and the mass gain of the composite samples were monitored during the water absorption from the environment. The dielectric measurements covered the frequency range from 0.1 Hz to 50 kHz. A theoretical model for the dielectric properties of composites with an interlayer describes the detected dielectric loss processes due to the electrically conducting layer of adsorbed water at the filler-matrix interface. A quantitative relationship between the amount of absorbed water and the frequency of maximum dielectric loss can be established by taking into account the thickness dependence of the conductivity of the interfacial water layer.