Compatibility Assessment of Fuel System Infrastructure Plastics with Bio-oil and Diesel Fuel

Bio-oil derived via fast pyrolysis is being developed as a renewable fuel option for petroleum distillates. The compatibility of neat bio-oil with 18 plastic types was evaluated using neat diesel fuel as the baseline. The plastic materials included polyphenylene sulfide (PPS), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyoxymethylene (POM), POM copolymer, high density polyethylene (HDPE), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene terephthalate glycol (PETG), polythiourea (PTU), four nylon grades, and four thermosetting resins. Specimens of each material were immersed in the test fuels for a period of 16 weeks to achieve full saturation. Except for PP and HDPE, the plastic materials underwent higher volume expansion in bio-oil than in the baseline diesel (which was negligible in most cases). This volume increase corresponds to the higher polarity of the bio-oil. PPS, PET, and PTFE were unaffected by bio-oil exposure, but modest swelling (between 2 and 5%) occurred for the two acetals (POM and POM copolymer), Nylon-12, PBT, PETG, and the four resin grades. More moderate swelling (8–15%) was noted for Nylon-6, Nylon-6/6, and Nylon-11, and excessive swell (>40%) occurred for PTU. The nonpolar nature of PP and HDPE matches that of diesel, leading to higher solubility (swell) in this fuel type. The relatively low volume expansion following exposure indicates that many of the existing infrastructure plastics (excluding PTU) should be suitable for use with bio-oil.