Microwave dielectric properties of rubber compounds undergoing vulcanisation

The application of microwave measurements to the characterisation of rubber compounds vulcanisation is considered. The change of mechanical and microwave (20 GHz) dielectric parameters during vulcanisation was measured for three kinds of compounds: Pure natural rubber, a compound with vulcanisation system and the corresponding compound containing carbon black. Changes of microwave dielectric permittivity and loss, probably caused by the change of concentration of the polar molecules and groups during vulcanisation, were detected. The difference in behaviour between unvulcanised and vulcanised compounds was clearly seen. Our study proves that microwave dielectric measurements are a highly sensitive and informative tool for following and monitoring the progress of vulcanisation reactions.