To validate the approach presented by Leblanc, we performed tests using several filled rubber compounds – including not only carbon black compounds but also silica rubber compounds. Experiments were run on Alpha Technologies’ Premier™ RPAs using FT-Rheology via LAOS. 

To confirm the predictive ability of the LAOS technique to evaluate the filler dispersion, we characterized a highly silica filled SBR/BR compound for tire application with the Premier RPA. The silica tread rubber compound was prepared with a suitable silica-silane reinforcing system and mixed on an internal mixer characterized by intermeshing rotors and an automatic adjustable rotor speed system, performing a two-mixing stage process.  

Lab technicians took samples from each stage at different mixing times – for example, at the beginning of the first mixing step (after 1 min.) and at the end of this stage.  – to determine if the full dispersion of the filler in the rubber matrix has been achieved, by the end of the mixing process. 

We performed a LAOS test on all samples taken from the mixer at different times as strain sweep subtests from ±30.0% to ±1000% strain at 100°C and 0.5 Hz.  By plotting the third relative torque harmonic versus strain for each compound sample, we were able to track the progress of the filler dispersion and the silanization reaction along the mixing line, see Fig 1.