Alternate instrumental methods of measuring scorch and cure characteristics

After the development of the oscillating disk curemeter over 30 years ago, standard conditions for measuring scorch times (time till the onset of vulcanization) were developed. ISO 3417 and ASTM D2084 describe ts1 and ts2 test parameters which are accepted by the rubber industry as a method for measuring scorch times. ts1 is the time until one torque unit rise above minimum torque and ts2 is the time until two torque units rise above minimum torque. These parameters are arbitrary and do not measure the ‘true’ scorch time. Also ts1 and ts2 may not be an accurate comparison for compounds which differ greatly in their state of cure. Experience has shown that some rotorless curemeter designs are far more sensitive to physicochemical changes occurring during the cure process than the conventional oscillating curemeters. The MDR 2000® rotorless curemeter (MDR) and the RPA 2000™ Rubber Process Analyzer (RPA) measure subtle changes in viscoelastic properties during the curing process. This paper discusses the feasibility of using the time until the viscous torque (S′') peaks (trmmaxS′') to more accurately measure the ‘true’ scorch time. Other techniques for measuring cure characteristics are also reviewed for comparison.