Ultrasonic and mechanical measurements for the detection of crosslink density of SBR and NBR based on various curing systems

The stress-strain measurements of styrene-butadiene rubber (SBR) samples based on various curing systems were used to access the crosslink density of various rubber mixes. Same materials were subjected to various uniaxial compression strains. The thicknesses before compression and after recovery were recorded. After recovery, pulse echo method was used to measure the ultrasonic velocity for the dilatational wave and that of shear wave at a frequency of 2 MHz and at room temperature. Both of the ultrasonic velocities were used to determine the elastic moduli of the samples. The relation between the elastic moduli and the corresponding recovery values were used to determine the crosslink density of samples. The crosslink density values obtained from the two techniques were compared. Butadiene-acrylonitrile (NBR) rubber mix was used to show that the ultrasonic technique is applicable for other rubber compounds.