The compatibility of plastic materials used in gasoline storage and dispensing applications was determined for test fuels representing neat gasoline (Fuel C), and blends containing 25% ethanol (CE25a), 16% isobutanol (CiBu16a), and 24% isobutanol (CiBu24a). A solubility analysis was also performed and compared to the volume swell results obtained from the test fuel exposures. The plastic specimens were exposed to each test fuel for16 weeks at 60°C. After measuring the wetted volume and hardness, the specimens were dried for 65 hours at 60°C and then remeasured for volume and hardness. Dynamic mechanical analysis (DMA), which measures the storage modulus as a function of temperature, was also performed on the dried specimens to determine the temperature associated with the onset of the glass-to-rubber transition (Tg).
For many of the plastic materials, the solubility analysis was able to predict the relative volume swell for each test fuel. Those plastic materials commonly used as permeation barriers exhibited the least amount of volume and hardness change (<5%) when exposed to the test fuels. The response of other plastics (especially nylon) varied according to type and grade. Nylon 6 and Nylon 6,6 showed the lowest property changes following exposure Fuel C and the isobutanol blends, but swelled over 7% when exposed to CE25a. Acetal and polybutylene terephthalate (PBT) swelled around 5% with exposure to the test fuels, while high density polyethylene (HDPE) swelled around 10% for each test fuel. The remaining thermoplastics swelled to higher values and in the case of polypropylene, dissolution occurred with exposure to gasoline containing 25% ethanol. The fiberglass resins experienced more swelling in CE25a when compared to the baseline fuel or the two isobutanol blends. In general, the plastics exhibited a positive volume change when dried, which was attributed to fuel retention. For many plastics the Tg was not measurably affected by the test fuel exposures. However, polyethylene terephthalate (PET) and the nylons were notable exceptions. The Tg for PET was reduced by 30°C with CE25a, while the reductions observed for nylon depended on both nylon grade and oxygenate type.
