Determination of thermal degradation of vulcanized rubbers using diffracted SH ultrasonic waves

Thermal degradation of NBR and CR heated in air was determined by analysis of diffracted SH ultrasonic waves. Thermal degradation was evaluated by exa mining wave pattern characteristics of SH waves passing through the surface depth between transmitter and receiver. Thermal crosslinking of main chain s in thermally degraded NBR and CR, accompanied by lowering of mechanical p roperties, can evaluate by decrease of launched time and appearance of 0.9 MHz side peak of the power spectrum. The thermal degradation also causes ph ase delay at high frequencies, showing regression of viscoelasticity associ ated with formation of dangling ends. (C) 1999 John Wiley & Sons, Inc.