Real-Time Ultrasonic Monitoring of the Vulcanization Process in Nitrile Rubbers

Nitrile rubbers, also known as Nitrile-Butadiene rubbers, belong to the category of synthetic rubbers and are a better choice as materials for applications requiring higher abrasion resistance and material adhesion. To meet the requirements, vulcanization of such rubbers to the appropriate level is necessary. Earlier, various spectroscopy-based experimental techniques and methods like nuclear magnetic resonance (NMR), chemical analysis, DMA analysis, differential calorimetric have been reported to be used to detect cure reaction of thermosets. In the present work, ultrasonic measurement techniques are employed on the rubber samples in a nondestructive manner via a test setup integrated with a fully automated ultrasonic data acquisition system developed in-house. Real-time monitoring of the vulcanization process of the rubber samples is carried out at different temperatures in order to capture the dependence of the rate of vulcanization on ultrasonic parameters. Tests are carried out at five different temperatures ranging from 140 to 180°C on nitrile rubber samples, and temporal variations of ultrasonic velocity and back wall amplitude are derived by post-processing the digitized data. Ultrasonic responses are observed to identify the rate of vulcanization and completion of the vulcanization process comprehensively. Observations are further consolidated by hardness measurements on the bounding faces of the rubber samples.