Chemical kinetics of vulcanisation and compression set

Different natural rubber-based masterbatches compounded using an efficient sulphur, conventional sulphur, peroxide, and diurethane vulcanisation systems were characterised in terms of cure behaviour, vulcanised to different levels of cure, and then tested for set in compression. Cure system, cure temperature, and duration of cure were amongst others, factors which influenced the rate of cure, the density of crosslinks in the vulcanisate network, as well as the set in compression of the vulcanisates. The reduction in compression set with extent of cure (modifications of the vulcanisate network structure) was exponential and could be characterised in terms of a structural modification constant which defines the rate of network modification with prolonged cure. This constant is similar to the reverse relaxation time in stress relaxation measurements.