Compatibility Assessment of Plastic Infrastructure Materials with Off-Highway Diesel and a Diesel Blend Containing 20 Percent Fast Pyrolysis Bio-Oil
The compatibility of plastic materials used in fuel storage and dispensing applications was determined for an off-highway diesel fuel
and a blend containing 20% bio-oil (Bio20) derived from a fast pyrolysis process. Bio20 is not to be confused with B20, which is a
diesel blend containing 20% biodiesel. The feedstock, processing, and chemistry of biodiesel are markedly different from bio-oil.
Plastic materials included those identified for use as seals, coatings, piping and fiberglass resins, but many are also used in vehicle
fueling systems. The plastic specimens were exposed to the two fuel types for 16 weeks at 60°C. After measuring the wetted volume
and hardness, the specimens were dried for 65 hours at 60°C and then remeasured to determine extent of property change. A solubility
analysis was performed to better understand the performance of plastic materials in fuel blends composed of bio-oil and diesel.
All of the plastic materials evaluated in this study exhibited higher solubility (volume swell) with the Bio20 fuel blend. This result was
predicted by the solubility analysis. However, there were two notable exceptions; the volume swell results for high density
polyethylene (HDPE) and polypropylene (PP) did not correlate with their respective solubility curves. HDPE and PP were also unique
in that they were the only two plastics that exhibited pronounced volume expansion in the baseline diesel test fuel.
The plastic materials which showed the best compatibility to the bio-oil blend were the barrier plastics polypropylene sulfide (PPS),
polyethylene terephthalate (PET or Mylar™), and polytetrafluoroethylene (PTFE or Teflon™). Polyvinylidene fluoride (PVDF or
Kynar™) is also used extensively as a permeation barrier material; however, it swelled over 15% when exposed to Bio20. Four grades
of nylon were evaluated and the petroleum-derived nylons (Nylon 6, Nylon 6,6, and Nylon 12) showed good compatibility with the
test fuels. In contrast, Nylon 11, which is derived from vegetable oil, expanded over 4% with Bio20. HDPE also swelled around 4%,
but did so with both test fuels. Two acetal materials and polybutylene terephthalate (PBT) were also observed to swell to 4% with
Bio20. Four fiberglass resins were included in the study and they exhibited 10-18% volume expansion. High volume swell was also
noted for PP, the PET polyethylene - glycol copolymer (PETG), and polythiourea (PTU). PP also expanded over 15% following
exposure to the baseline diesel test fuel.