For the use in packer elements for oil exploration, rubber materials are required that can withstand high mechanical loads, high temperatures, and aggressive chemical media. To fulfill these demands, we designed composites of hydrogenated acrylonitrile butadiene rubber filled with both carbon black and short cut aramid fibers. Scanning electron micrographs indicate a strong connection between the resorcinol formaldehyde latex fiber coating and the peroxide-cured rubber matrix. During the preparation of the test specimens, especially care was taken to obtain samples with very well-defined fiber orientations. We studied the effect of fiber anisotropy on the hardness and on the mechanical properties under uniaxial elongation and cyclic compression at room temperature and 1508C. The strongest reinforcing effect is observed when the fibers are oriented along the main direction of deformation. For tensile test, this is the case, as expected, for fibers oriented parallel to elongation. For compression tests on cylindrical specimens, we find that the fiber orientation perpendicular to compression direction is most effective. At 20-40% strain, tensile tests exhibit a pronounced yield stress which is likely the result of the loss of adhesion between the rubber matrix and the fibers. Repeated loading and unloading compression tests reveal a considerable stress softening effect between the first and second cycle for fiber-filled composites. At 1508C, the rubber composites soften considerably, but small amounts of fiber still induce a significant reinforcement. POLYM. COMPOS., 00:000-000, FIG. 9. SEM-Micrographs of a RFL-coated aramid fiber (a), a fiber located at the fracture surface of a tensile test specimen with fibers oriented in L-direction (b), and fracture surfaces of composites with 80 phr CB, 6 phr peroxide, and 6 phr AF with fibers oriented in L-and T-orientation, (c) and (d), respectively.
Sulfur can be used as crosslink coagent in unsaturated elastomer. In this work, a fully saturated HNBR with 39 wt % nitrile content was selected to investigate the effect of a small amount of sulfur acting as crosslink coagent on the physical and mechanical properties of peroxide-cured vulcanizates. First, selective cleavage of polysulfide (ASxA) and monosulfide(ASA) bond by combined thiol-piperidine treatment were performed and the existence of poly/monosulfide bond in sulfur-contained HNBR compounds was verified. Then, no-filler HNBR compounds with various content of sulfur were investigated to detect the influence of sulfur on the crosslink density and cure kinetics. The MDR results showed that the crosslink density of HNBR compounds reduced only when the amount of sulfur is 0.25 phr and above. Besides, the curing rate of no-filler HNBR compounds increased with the increasing of the amount of sulfur and reached a maximum at a dosage of 0.25 phr sulfur. Finally, physical and mechanical properties of fully formulated compounds were evaluated and it was found that the addition of small amounts of sulfur in fully saturated HNBR compounds could improve the dynamic properties of peroxide-cured HNBR compounds remarkably but at a cost of slightly higher compression set values and a small loss in heat aging resistance. In a conclusion, small amount of sulfur can impart the peroxide vulcanizates some "sulfide properties" like dynamic property, tensile strength, but at the same time, due to the introduction of sulfur, some "peroxide vulcanizates property" like heat-resistance property, hot air resistance were weakened slightly.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.