Comparison of Graphite and Graphene Precursors in HNBR

High shear mixing of expanded graphite produced a small but statistically significant reduction of permeability in HNBR at a shear rate of about 20,000 second^-1, though the small reduction of permeability due to high shear mixing was less than the differences observed between different grades of graphite, and is not believed to indicate exfoliation to graphene. The research showed that high degrees of reinforcement and enhanced permeation resistance are seen with dispersions of expanded graphite compared to micronized graphite. The bulk density of expanded graphite as initially produced (“vermiform”) is extremely low, 0.004 g/cc in the sample used in this study. Vermiform expanded graphite was compared to four commercially available grades of graphite,  including two commercially available grades of expanded graphite, at equal volume loading of graphite or carbon black (used in the control compound), in peroxide-cured HNBR. Permeation of an aliphatic permeant (trimethylpentane) was significantly lower for HNBR compounds containing all grades of graphite tested compared to N-550 carbon black. The expanded graphite grades produced significantly lower permeation than the micronized natural graphite, and the vermiform lab expanded graphite produced the lowest permeation rate of any of the fillers tested. Blistering is observed in HNBR, IIR, BIIR, and ethylene/octene copolymer elastomers when high levels of expanded graphite is used as a reinforcing filler.