DC-electrical conductivity as a method for monitoring radiation curing of unsaturated polyester resins III. Evaluation of results

Abstract

The results of DC-electrical conductivity monitoring of radiation and thermally initiated crosslinking of unsaturated polyester resins are interpreted using conductivity data itself instead of commonly used logarithmic data form. The main setbacks of logarithmic conductivity data were the shift toward longer reaction time compared to non-logarithmic conductivity data and extraction analysis results and pronounced scattering at the end of the reaction so it was impossible to detect vitrification point. By revision of approach to analysis of results, full sensitivity of the electrical conductivity method to structural changes in the reacting system was shown. The apparent rate constants calculated from conductivity itself showed the influence of upper liquid–liquid transition on the rate of radiation induced reaction that could not be seen if the logarithm of conductivity was used. Influence of dose rate effects and electrical field effects on reaction rate were detected too and confirmed by DSC measurements. All details of reaction can be detected using first derivative of conductivity and in the case of thermally initiated reaction two maxims of reaction rate were found that are probably caused by local increase of temperature due to highly exothermic reaction.