Aging of anhydride-hardened epoxies in lubricants at elevated temperatures
In automotive under-the-hood applications, electronics respectively their packaging materials come in contact with automotive fluids. The effect of automatic transmission fluid (ATF) on an anhydride-cured epoxy was investigated at temperatures up to 180 8C for up to 1000 h. This study has shown that ATF retards the oxidative aging of the epoxy, presumably due to oxygen consumption. Where as in air the material underwent a thermo-oxidative aging with a mass loss of up to 4% and a strong broadening of Tg to higher temperatures, in ATF a temperature dependent distinctive drop of Tg from 142 8C to 126 8C after 1000 h aging at 180 8C, and a mass loss of maximum 1% was observed which might be a thermal decomposition of the epoxy material. A slight broadening of the damping factors might indicate an intrusion of ATF components. A color change of the samples could be observed after aging in air and ATF, with the discoloration in air being more intense. An explanation for the color change might be either a minor amount of oxygen causing an oxidative discoloration reaction or the intrusion of colored ATF degradation products. While the oxidation-kinetics in air exhibited Arrhenius temperature-dependence the mechanism in ATF changed above 165 8C. An acceleration of aging tests at temperatures beyond 150 8C is therefore not possible.
Robert Bosch GmbH, Robert-Bosch-Campus 1, Renningen 71272, Germany & Faculty for Production Engineering-Mechanical Engineering & Process Engineering, University of Bremen, Badgasteiner Strasse 1, Bremen 28359, Germany