The effect of temperature on the properties of the NBR/PVC blend exposed to ethanol fuel and different gasolines

Abstract

The use of ethanol fuel or ethanol/gasoline mixtures has greatly increased in recent years. The effect of the fuels on the stability of the polymeric components of vehicles is an important point of investigation, especially taking into account that other solvents are sometimes used to adulterate the ethanol/gasoline mixtures. To assess the compatibility of the fuel with the NBR/PVC blend, we studied the changes in the weight, hardness and mechanical properties of this polymeric blend during the immersion tests with different gasolines (regular, premium, regular doped with rubber solvent and regular with addition of cyclohexene) and with bioethanol fuel. The immersion tests were performed by 20days at immersion temperatures of 30°C, 60°C and 110°C. The diffusion coefficients related to the fuel sorption and desorption processes were calculated. The values of the parameters Tau3 and I3 were obtained by positron annihilation lifetime spectroscopy (PALS) to investigate the free volume of the NBR/PVC blend. All of the blend samples became less elastomeric and more rigid after the exposure tests. The swelling of the NBR/PVC blends exposed to the different gasolines increased with the immersion temperature. The NBR/PVC blend samples exposed to the gasoline doped with cyclohexene showed a two-fold increase in swelling compared with the other gasolines. The samples immersed in bioethanol showed the highest weight loss due to the polar character of the alcohol, which caused the extraction of a large quantity of the polymeric blend constituents. The pure ethanol was more aggressive for NBR/PVC blend than all of the Brazilian gasolines studied.