Migration of Antiozonant from Neoprene Hose Covers

Certain fuel line hoses having neoprene covers and nitrile inner tubes and test slabs of these materials were subjected to accelerated heat, fuel, and ozone exposure. Results indicate some neoprene hose covers can lose ozone resistance after severe test exposure to heat and/or fuel circulation. Chemical analysis indicates that one type of antiozonant, nickeldibutyldithiocarbamate, is extracted out of the neoprene cover by fuel circulation through the inner nitrile tube. Similarly, heat aging causes a migration of this antiozonant from the neoprene cover into the nitrile tube. These two factors are largely responsible for the loss of ozone resistance. Extraction of plasticizing oil also occurs during fuel circulation with subsequent hardening of hoses. However this contributes only in a secondary manner to the observed loss of ozone resistance. Test conditions for candidate fuel line hoses are recommended to provide improved ozone resistance. Both Hypalon (chlorosulfonated polyethylene) and EPDM (ethylene-propylenediene monomer) hose covers show no evidence of cracking in ozone after heat aging and fuel circulation. One of these improved hose covers has been incorporated into all production vehicles for some time now.