Physical and chemical effects of biodiesel storage on high-density polyethylene: Evidence of co-oxidation

• Published in: Polymer degradation and stability 2019-03, Vol.161, p.139-149
• Main Authors: Erdmann, Maren, Böhning, Martin, Niebergall, Ute
• Format: Article
• Language: English
• Subjects: Biodiesel fuels; Biological evolution; Carbonyls; Chemical effects; Crystal structure; Crystallinity; Deformation mechanisms; Degradation; Diesel; Diesel fuels; Elongation; Esters; Fossil fuels; Fourier transforms; High density polyethylenes; Infrared spectroscopy; Long-term storage; Necking; Organic chemistry; Oxidation; PE-HD; Plastic deformation; Polymers; Renewable resources; Sorption; Storage tanks; Stress-strain curves; Stress-strain relationships; Tensile test; Tensile tests
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2019.01.018

The physical and chemical effects of diesel and biodiesel fuels on two high-density polyethylene (PE-HD) types were investigated. Both semi-crystalline PE-HD are common thermoplastic materials for container and storage tank applications. Biodiesel, a composition of unsaturated fatty acid esters from renewable resources, was chosen as it is regarded a possible green alternative to fossil fuels. The study aims at identifying significant differences between biodiesel and conventional diesel fuels based on the differences in the chemical nature of the two. The physical effects of the fuels on the polymer at first comprises the sorption behavior, i.e. kinetics and final equilibrium concentration. Not only are both fuels absorbed by the amorphous phase of the semi-crystalline PE-HD, they also induce a plasticization effect that modifies the molecular mobility and therefore also the characteristic yielding properties, manifest in the obtained stress-strain curves. The chemical effects related to degradation phenomena is investigated by a long-term storage scenario using partially immersed tensile test specimens in diesel and biodiesel. We were able to confirm the proposed co-oxidation mechanism by Richaud et al. for polyethylene-unsaturated penetrant systems on a larger scale based on practical tensile tests. One of the investigated polyethylene grades subjected to tensile drawing showed a significant loss of plastic deformation and the onset of premature failure after 150 days of storage in biodiesel. Further biodiesel storage showed a systematically reduced elongation at break before necking. None of these effects were observed in diesel. Oxidation of fuels and polymer after progressing storage times were analyzed by the evolution of carbonyl species in FT-IR/ATR spectroscopy. [Display omitted] •Sorption of biodiesel and diesel leads to plasticization effects with respect to mechanical properties of PE-HD.•Long-term storage of partially immersed PE-HD shows indications for premature degradation at the air-biodiesel interface.•Tensile fracture of exposed specimens occurred specifically at the air-biodiesel interface.•Oxidative degradation was not observed for long-term diesel storage – evidence of co-oxidation effect of biodiesel.