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.
Tian H, Chen Q, Liu Z, Zhang M, Abolfathi S
Summary
7.9/10A two-year field study compared how quickly different plastic coatings used on fertilizers break down in soil, finding that plant-based polyurethane coatings degrade about 2.2 times faster than petroleum-based versions while producing fewer toxic byproducts, offering a more sustainable solution to reduce microplastic pollution from agricultural inputs.
Key Findings
Starch-based polyurethane (SPU) coatings degraded 2.2 times faster than conventional petroleum-based polyester polyurethane (PPU) over an 807-day field experiment
SPU coatings would take approximately 75 years to degrade by 90% in deeply buried soil, compared to 163 years for conventional PPU
Biobased polyurethane coatings produced fewer toxic byproducts in soil than petroleum-based PPU while exhibiting more porous microstructures and higher degrees of fragmentation
Original Abstract
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.