Ageing properties of a polyoxymethylene copolymer exposed to (bio) diesel and hydrogenated vegetable oil (HVO) in demanding high temperature conditions

Abstract The increasing use of renewable biofuels in the transportation sector has driven attention on the incompatibility issues between biofuels and the polymeric materials used in the vehicle fuel system. Here, the ageing effects on a polyoxymethylene copolymer exposed to four types of fuels; petroleum diesel, biodiesel, a commercial mixture of these, and hydrogenated vegetable oil (HVO) at demanding high-temperature conditions, were investigated and compared with its performance in air. The degree of material degradation during ageing was highest in the presence of the non-polar fuels (HVO/petroleum diesel). The samples aged in different fuels underwent the same increase in crystallinity due to annealing. Surface powdering was observed on the sample aged in the fuel mixture. The negative effects from a combination of plasticization and swelling, induced by the sorbed fuel, oxidation and surface cracks dominated the changes in mechanical properties, leading to reduced stiffness, strength and extensibility. The results indicate that care should be taken when choosing this polymer in contact with, especially, non-polar fuels at severe conditions.