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Long-term localization experiments reveal aging degradation mechanisms of biobased and petroleum-based polyurethanes in natural environments: degradation characteristics, product assessment and degradation cycle prediction
Summary
Researchers conducted a 807-day field localisation experiment to study the degradation mechanisms of biobased and petroleum-based polyurethanes used as polymer coatings on controlled-release fertilisers in natural soil environments. The study characterised the degradation products, assessed environmental risk, and developed a predictive model for the degradation cycle, finding that both polyurethane types fragment into microplastic residues at different rates.
The widespread use of polymer-coated controlled release fertilizers has raised concerns, as it may become a new source of microplastic pollution in the environment. However, there is limited knowledge on the transport and fate of different types of polyurethane in soil. We conducted a 807-day field experiment to compare the degradation characteristics of conventional polyester polyurethane (PPU) coatings with novel, biobased coatings from liquefied starch-based polyurethane (SPU) and castor oil polyurethane (CPU). The biobased coating SPU degraded 2.2 times faster than the petroleum-based PPU. After degradation, biobased coatings exhibited a more porous microstructure, higher concentrations of oxygen and dissolved organic matter, more oxygen-containing functional groups, and higher degrees of fragmentation, consistent with greater aging. It is estimated that the starch-based polyurethane coating would take approximately 75 years to degrade by 90 % in deeply buried soil, which is significantly faster than its petroleum-based counterpart (163 years), highlighting the importance of shifting toward biobased products that degrade more quickly. Biobased coatings also produced fewer toxic byproducts in soil than petroleum-based PPU products. These results clarify the degradation processes of polyurethane coatings and improve our understanding of the fate of polyurethane microplastics in soils.
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