Accelerated Heat-Aging Studies on Fluororubber in Various Media

The nature, extent and, rate of chemical changes that take place in certain elastomers at long times is being studied. The chemical degradation of styrene-butadiene rubber (SBR) and fluorosilicone rubber (FVMQ) were reported previously. Investigations carried out with fluororubber (FKM) are discussed in this paper. Like fluorosilicone, this fluorocarbon elastomer is regarded as a high-temperature- and hydrocarbon-fuel-resistant rubber. The designation FKM is given to the copolymers of vinylidene fluoride (VF) and perfluoropropylene (PFP). The one discussed here is reported to contain also small quantities of a third component, tetrafluoroethylene. The detailed structure, assigned to the FKM polymer as a result of nuclear magnetic resonance studies, shows that it consists of blocks of VF homopolymer, 95% of which is head-to-tail, and blocks of VF-PFP copolymer, 93% of which is head-to-tail. The ratio of the copolymer to the VF homopolymer is dependent on the mole fraction of VF used. Vulcanization of FKM with derivatives of diamines is the commercially preferred method, although peroxides and high-energy radiation can be used for the same purpose. In the present study, N, N-dicinnamylidene-1,6-hexanediamine a Schiff 's base of 1,6-hexanediamine, was used with magnesium oxide as the acid acceptor. Chemical stress relaxation was the method most extensively used to determine the network changes taking place in the heat-aged fluororubber. Swelling, gel permeation chromatography (gpc), and infrared (ir) spectroscopy were also used to obtain additional information.