Long-term performance of a polyamide-12-based fuel line with a thin poly(ethylene-co-tetrafluoroethylene) (ETFE) inner layer exposed to bio- and petroleum diesel

• Published in: Polymer degradation and stability 2018-10, Vol.156, p.170-179
• Main Authors: Wei, Xin-Feng, Kallio, Kai J., Bruder, Stefan, Bellander, Martin, Gedde, Ulf W., Hedenqvist, Mikael S.
• Format: Article
• Language: English
• Subjects: Ageing; Annealing; Biodiesel; Biodiesel fuels; Carbon black; Diesel; Diesel fuels; Electrical conductivity; Electrical resistivity; Ethylene; Ethylene tetrafluoroethylenes; Fluorine containing polymers; Fluoropolymers; Fuel lines; Fuel pipe; Fuel pipes; Gasoline; Glass; Glass transition; Glass transition temperature; High temperature; Isothermal conditions; Long term performance; Low level; Migration; Modulus of elasticity; Motor vehicles; Oxidation; Pipes; Plasticizer loss; Plasticizers; Poly(ethylene-co-tetrafluoroethylene); Polyamide; Polyamide resins; Polyamides; Polyamines; Polyethylene terephthalate; Reinforced plastics; Tetrafluoroethylene
• ISSN: 0141-3910; 1873-2321; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2018.09.003

The long-term performance of a polyamide-12 (PA12)-based (bio)diesel fuel line/pipe with a thin poly(ethylene-co-tetrafluoroethylene) (ETFE) inner layer was investigated in “close to real” and high-temperature isothermal conditions with fuel on the inside and air on the outside of the pipe. The inner carbon-black-containing ETFE layer resisted fuel attack, as revealed by the small fuel uptake, the very low degree of oxidation, and the unchanged electrical conductivity, glass transition and melting behaviour. The properties of the ETFE layer remained the same after exposure to all the fuel types tested (petroleum diesel, biodiesel and a blend of 80% diesel with 20% biodiesel). Because of the presence of the ETFE layer on the inside, the fuel pipe experienced noticeable changes only in the outer PA12 pipe layer through migration of plasticizer, annealing and slight oxidation. The evaporation of plasticizer was found to be diffusion-controlled and it led to an increase in the glass transition temperature of PA12 by 20 °C. This, together with a small annealing-induced increase in crystallinity, resulted in a stiffer and stronger pipe with an increase in the flexural/tensile modulus and strength. The oxidation of PA12 remained at a low level and did not lead to an embrittled pipe during the simulated lifetime of the vehicle. This study reveals that fluoropolymers have a great potential for use as fuel-contacting materials in “demanding” motor vehicle fuel line systems. •The ageing properties of a polyamide-12 (bio)diesel fuel line with a thin ETFE inner layer were investigated.•The fuel lines were aged in “close to real” conditions with fuel on the inside and air on the outside of the pipe.•This study reveals an excellent resistance of ETFE to fuel/(bio)diesel attack.•The ageing processes of the PA12 layer involved plasticizer migration, oxidation, annealing and stiffening of the material.