Evaluation of Aged Tires with Innerliners Containing Varying Halobutyl Levels

Tires made with 100-phr bromobutyl rubber, 80/20 bromobutyl/natural rubber, and 60/40 bromobutyl/natural rubber innerliners were evaluated to understand the effect of the halobutyl rubber content in the innerliner compound has on tire aging.  Each of the tires was oven aged for 6 weeks at 70°C and subsequently run on a 1.7-m roadwheel according to the FMVSS 139 Endurance test.  Optical micrographs showed the strong effect of halobutyl content on tire durability.  The crack length decreased with increasing halobutyl rubber content.  Modulus profiling showed the details of the aging in each tire type.  The indentation modulus analysis was performed at various locations: under groove, under lug, centerline, and belt edge.  In all locations the advantages of the innerliner were quantified.  In all locations halobutyl rubber provided an advantage in aging (oxidation) resistance, and the extent of the advantage varied with location.  Diffusion Limited Oxidation (DLO) modeling substantiated the aging resistance benefits of halobutyl rubber innerliners and agreed with the results of modulus profile measurements.  The DLO model predicted a stronger effect of tire innerliner on the oxidation rate than of other internal components during roadwheel testing than oven aging.