Influence of Surface Modification of Montmorillonite on Dielectric Properties of Epoxy-based Composites

Many polymer-based electrical insulating composites containing a proportion of mineral fillers up to tens of weight percent are being prepared in the present time. Used fillers, often as flame retardants, are commonly modified with surfactants primarily to provide better filler dispersion in the polymer matrix. Currently, high interest is given to the good dispersion of particles and the processing of as homogeneous material as possible; nevertheless, potential adverse effects of such modification, often with strongly polar character, on important dielectric parameters of the material are analyzed in detail rarely. This problem will be emphasized in this paper, which compares the dielectric properties of composites based on the epoxy resin with the addition of montmorillonite clay without and with surface modification (by quaternary ammonium salt). Monitored loss factor representing dielectric losses in materials prove that the effect of the montmorillonite modification is negative in a certain frequency and temperature interval. The observed loss factor increases caused by the surface modification of montmorillonite is approximately threefold at 50 Hz and 50 °C (common operating conditions). It is advisable to pay attention to optimizing the incorporation of mineral fillers as a multi-step homogenization of mineral fillers within the polymer composites processing for electrical insulation systems. Only when the required level of filler dispersion has not been achieved by optimizing of filler incorporation without modification, the usage of modification designed to improve dispersion is well-founded.