Dielectric permittivity and breakdown characteristics of polymer-mica composites

Abstract

Novel and economically promising polymer/mica composites have been produced by microwave-plasma irradiation of micaflakes in ethylene prior to incorporation into a polyethylene matrix . These materials have good melt flow properties, favorable filler alignment, and controlled interfacial characteristics. This has prompted us, firstly, to carry out "diagnostic" measurements of the interfacial polarization (MaxwellWagner effect) and, secondly, to evaluate these composites from the point of view of their possible interest in high voltage insulation technelogy. IntroductionIn recent years the use of pol ymer-based composites has become wide-spread in diverse applications. The mechanical properties of such composites can often be significantly enhanced by the suitable choice of f iller materials, flake particulates and fibre-shaped solids being well-known reinforcing agents for a wide range of commodity polymers!.Adhesion at the polymer-matrix interface is one of the most important variables in the formulation of such composite materials, and a variety of coupling agents (eg silanes) have been developed to promote this adhesion. Encapsulation of fillers by polymers synthesized on the reinforcing solids, when these are used as catalyst supports in the polymerization, is al so a recognized route towards performance improvement 2 , but both of these methods are time-consuming and tend to add significantly to the cost of the reinforcing processes.We have developed a surface treatment technique for fillers which consists of irradiating the filler particles in a "cold" microwave plasma using the recently developed LMP apparatus (Large Volume Microwave Plasma Generator) 3, prior to incorporating them in the polymer matrix. This technique has several advantages: in contrast to conventional procedures, it is brief (generally of the order of seconds), simple, and involves only low-cost materials.In the work described here, Suzorite™ mica flake (60/100 mesh) was irradiated in an LMP discharge in ethylene vapor. This treatment results in the formation of a thin olefinic polymer layer on the mica flakes which substantially modifies the physical properties of polymerie composites incorporating the treated mica: Rheological (melt flow) and tensile measurements indicate that strong interfacial bonds exist between plasma-treated filler particles and polyolefin matrices 4 . * Senior Member IEEE

Electrical properties of polymers

“…Cooper (339) shows the effects of prestress on the density of traps of polyethylene films. Wertheimer et al (347) present a novel composite (polyethylene/mica) which is felt to hold some promise in high voltage insulating technology.…”