Soil experiment finds slow aging in already weathered plastics
Already weathered plastics retained most of their bulk properties after another 581 days buried in soil near Dijon, France. Researchers compared halves of 29 pieces, keeping one half in dark storage. Some surface oxidation measures declined, potentially as oxidized layers detached. The experiment distinguishes surface changes from the degradation of an entire plastic piece.
Science··Morning
Little change beneath the surface
Plastics already weathered in agricultural soils retained most of their bulk properties after a further 581 days underground. The peer-reviewed field experiment, published on November 5, followed 29 pieces representing films, rigid fragments and fibers. Most measurements of crystallinity, thermal stability and available molecular weights showed little change. The samples came with unknown exposure histories, so the results describe continued weathering of existing debris rather than the complete lifetime of a newly manufactured plastic product.[1]
Two halves for comparison
Researchers divided each piece and buried one half roughly ten centimeters deep at the same site outside the French city of Dijon. The other half remained in dark storage. The selection covered polyethylene, polypropylene, polystyrene and polyethylene terephthalate, commonly abbreviated PET. Analyses compared surface chemistry and morphology with bulk properties where enough material was available. Molecular-weight measurements covered polystyrene and PET only, because the other polymers could not be dissolved using the available procedure. Some pieces also lacked enough material for all the tests.[1]
A falling oxidation indicator
Some polyethylene and polystyrene surfaces had a lower carbonyl index, a measure of oxidation. The authors suggest that highly oxidized outer layers may have fragmented and detached. Small fragments were not directly tracked, leaving that mechanism an interpretation rather than a measured particle-release rate. Leaching, biological processes and cleaning could also contribute. A lower surface indicator therefore cannot establish that the whole polymer degraded. The study distinguishes surface alteration from bulk change and cautions against using oxidation alone to estimate environmental age.[1]
