The compatibility of plastic materials used in fuel storage and dispensing applications was determined for test fuels representing gasoline blended with 25 vol.% ethanol and gasoline blended with 16 and 24 vol.% isobutanol. Plastic materials included those used in flexible plastic piping and fiberglass resins. Other commonly used plastic materials were also evaluated. The plastic specimens were exposed to Fuel C, CE25a, CiBu16a, and CiBu24a for 16 weeks at 60oC. After measuring the wetted volume and hardness, the specimens were dried for 65 hours at 60oC and then remeasured for volume and hardness. Dynamic mechanical analysis (DMA) was also measured on the dried specimens.
The plastic materials used as permeation barriers exhibited the least amount of properly change when exposed to the test fuels. The performance of nylon was highly dependent on the grade; of the four nylons evaluated, Nylon 6 and Nylon 6,6 showed the lowest property change following exposure to Fuel C, CiBu16a and CiBu24s, 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 CE25a. The fiberglass resins experience more swelling in CE25a that with the Fuel C or the two isobutanol blends. In general, the plastics exhibited a positive volume change when dried, which was attributed to fuel retention. In addition CE25a produced a higher degree of property change than the other test fuels.
 

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Tim Theiss
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Oak Ridge National Laboratory
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