Investigation into the fatigue resistance of natural rubber vulcanisates

Abstract

The fatigue resistance of dicumyl peroxide (DCP) and conventional sulphur cured Natural Rubber (NR) vulcanisates have been investigated. The rubbers were examined both with and without hot acetone extraction under nitrogen, before and after vulcanisation. Extraction reduced the fatigue life of vulcanisates made by both procedures i.e., before and after vulcanisation. The non-rubber constituents of NR were shown to exhibit anti-fatigue activity in both vulcanisates, but the effect was more pronounced in DCP vulcanisates. Extra-network compounds produced by both vulcanising systems did not show any adverse effect on fatigue life. The fatigue life of DCP vulcanisates was found to be very dependent on DCP loading. Below 2 parts per hundred of rubber, the fatigue life was found to be higher than a conventional sulphur vulcanisate cured to the same rheometer torque. The structures resulting from DCP vulcanisation of NR have been studied by infra-red and it is shown that aromatic compounds, almost certainly derived from the cumyloxy radical, are attached to the crosslinked polymer. In the presence of IPPD, the DCP cured rubbers have a lower modulus than the control, and attempts have been made to find coagents to compensate for this. Trimethylol propane trimethacrylate was shown to satisfy this requirement; however, it showed an adverse effect on fatigue life.