Scheme of the used specimen with typical damage pattern observed in the interfacial zone between biodiesel and air after 150 days at 60 °C
Source: BAM, Division Mechanics of Polymers and Division Technical Properties of Polymeric Materials
Fuels from renewable sources as for example biodiesel are still of increasing importance – as replacement or especially as additive to conventional fossil fuels. As a typical container material high-density polyethylene (PE-HD) is used also for storage and transport of chemicals and dangerous goods as well as for fuel tanks. For the latter the question is raised to what extent the material behavior in contact with biofuels differs from that in contact with conventional fuels.
First, biodiesel as a fatty acid methyl ester (FAME) exhibits a higher polarity compared to diesel which causes differences with respect to the immediate interaction with the container material – in case of PE-HD e.g. the solubility and the resulting plasticization affecting mechanical properties. At the same time biodiesel is much more prone to oxidation than diesel. The reported investigation of the long-term behavior covering about two years shows that this may cause a much more pronounced oxidative degradation of the PE-HD – locally where biodiesel is in contact with the container material and the oxidizing air atmosphere simultaneously. Thus, by systematic investigation based on mechanical properties and microscopic analysis of fracture surface and fracture zone the co-oxidation of polyethylene by biodiesel is proven in a practical setting. Hence, in contact with diesel such degradation phenomena were not observed. A second PE-HD material with a distinctly higher content of stabilizing antioxidants does not show signs of a significant oxidative deterioration within the covered period of time.
Physical and chemical effects of biodiesel storage on high-density polyethylene: Evidence of co-oxidations
Maren Erdmann, Martin Böhning, Ute Niebergall
published in Polymer Degradation and Stability 2019, Volume 161, Pages 139 - 149
BAM, Mechanics of Polymers division and Technical Properties of Polymeric Materials