Elastomer compatibility test of alternative fuels using stress-relaxation test and FTIR spectroscopy

Global efforts to reduce CO₂ emissions and to tackle the problem of depleting petroleum resources have stimulated the exploitation of alternative fuels in the aviation industry. One crucial aspect amongst others is to investigate the compatibility of alternative fuels with elastomeric materials currently used in gas turbine engines. However, little knowledge about this has been understood so far for commercial aircrafts under real engine conditions. This study combines Stress-Relaxation test and FTIR spectroscopy techniques to look at the effect of alternative fuels on O-rings made from different materials; such as nitrile, fluorocarbon and fluorosilicone. Results indicated that after immerged in fuels for a period of time while simultaneously being compressed at certain temperatures, the fluorocarbon O-rings showed minimum change in the eight types of fuels tested. This meant they are compatible with these fuels, with the nitrile O-rings changing the most. Furthermore, FT-SPK+20% hexanol caused the biggest relaxation in fluorosilicone O-rings but had the smallest effect on nitrile ones while all fuels presented similar behavior in fluorocarbon. FTIR spectrum analysis showed molecular composition changes are dependent on the reactions between different materials and fuels. For fluorosilicone O-rings, the absorbance reduction from 1150 to 1050 cm^-1 was caused by the breakdown of (Si-O-Si) while the formation of new O-H bonds enhanced the intensity from 3000 to 2800 cm ^-1. For fluorocarbon O-rings, obvious increase in absorption could be found in the region from 1400 to 650 cm^-1, while from 3000 to 2800 cm^-1, the absorption decreased. Multiple linear regression analysis indicated a highly correlated relationship between the chemical structure changes and the force relaxation.