The Effect of Solvent on the Crazing of Enameled Wires

Abstract

The effect of solvent on crazing of enameled wires is discussed in the light of rheological data obtained for enameled polymer films. The enamels studied were polyesterimide, modified polyvinyl formal, trimellitic polyamideimide, and Nylon 66. The test wires were specifically prepared by coating these polymers on an oxidized conductor whose adhesion to the polymers was poor, and they were subjected to rheological measurement after treatment by various solvents. Two types of solvent effect were observed on the stress relaxation curves under constant elongation. In one, there was an abrupt change in the stress relaxation rate upon application of the solvent, and in the other, a stress growth for a certain period resulting in a stress relaxation curve with a maximum. This difference seemed to be attributable to the nature of the solvent rather than to the polymer, at least within the tested combinations of polymers and solvents.
The mechanical tan curves of the polymer films stripped from wires were also investigated, with and without application of solvents. It has been found that the shift of the glass transition temperature caused by the solvent is a good measure of the solvent effect on crazing of enameled wires. That is, a solvent which lowers more markedly the glass transition temperature of a given polymer film shows a greater tendency to cause crazing.