NBR Vulcanizates Resistant to High Temperature and “Sour” Gasoline

Abstract

Abstract NBR compounded in a conventional fuel hose tube formulation is markedly degraded by “sour” gasoline or “sour” ASTM Fuel C within 7 days at 40°C. Furthermore, the conventional NBR compound is not resistant to aging at 125°C. Use of an NBR designed for heat resistant compounding and an appropriate choice of compound greatly improve resistance to fuel which contains hydroperoxides. The preferred system for “sour” gasoline resistance and resistance to long term aging at 125°C is a cadmium oxide activated low sulfur-sulfur donor compound with silica as the principal filler. This vulcanizate is not much more affected after 7 days at 40°C by gasoline of peroxide number 50 than by clean gasoline, and is less affected by gasoline of peroxide number 200 than are other NBR vulcanizates. The balance of high and low temperature properties can be optimized by appropriate choice of plasticizer and acrylonitrile level. Aging resistance is somewhat improved by increase in acrylonitrile content, and fuel permeability is markedly decreased. Permeability to gasoline with 30 aromatic content can be changed appreciably by compounding, but the resistance to Fuel C with 50% aromatic content does not appear to respond to compounding changes. The stability of NBR vulcanizates in “sour” gasoline is reduced by copper salts and, to a lesser extent, by metallic copper. Bound antioxidant NBR does not appear to offer an advantage in “sour” gasoline resistance over heat resistant NBR compounded in a comparable formulation.