The thermal step technique: an advanced method for studying the properties and testing the quality of polymers

Abstract

It is well known that the physical properties of a polymer alter with time. This phenomenon—ageing—is strongly related to the external factors acting upon the polymer and to the manufacturing process. An appropriate process could prevent the premature and undesired changes in the characteristics of a polymeric material. For this reason, considerable efforts are made to understand the mechanism of polymer degradation. Past studies have shown that the existence of electrical charges in the bulk of polymers can affect their properties significantly. These charges—usually called space charges or space charge—were first observed in polymers used for electrical insulation and therefore submitted to high electric fields. Some recent studies, particularly those presented in this paper, proved that space charge exists in almost every polymer. It has been shown that space charge can be present within the material from the very manufacturing process, without previous submission to stress. The increase of the amount of the space charge seems strongly related to the deterioration of the physical properties of polymers. Space charge measurements can therefore be considered as a test of quality for polymers. This paper is dedicated to a method for measuring space charge: the Thermal Step Method (TSM). The physical basis of the technique, as well as its applications, are presented. Results obtained on various polymers are presented and discussed. The results show that the features of this technique, particularly its high sensitivity, make it an appropriate tool for the characterization of a wide variety of materials. The TSM could also be associated with other physical, chemical or physico-chemical techniques. © 1998 SCI.