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Influence of additives on long-term degradation and microplastic formation of polyethylene
Summary
Common plastic (LDPE, used in packaging) breaks down into microplastics much faster when it lacks UV-blocking additives, cracking apart within just 600 hours of sun exposure. Even the best additive tested couldn't fully stop the plastic from shedding tiny microplastic particles over time—it just slowed the process down and changed the size and makeup of the particles produced. This matters because it shows that the additives added to plastic packaging don't just affect how long products last on shelves—they directly influence how much and what kind of microplastic pollution ends up in our environment and, potentially, in our food.
There are limited studies showing how additive contents used for packaging plastics affect polymer degradation and microplastic formation. Hence, we used accelerated abiotic weathering for studying the mechanisms leading to the degradation of additivated, semi-crystalline low-density polyethylene (LDPE). For this purpose, LDPE plates with different, realistic concentrations of additives (antioxidants and UV stabilizers) were weathered in an accelerated weathering chamber and analyzed using SEM, DSC, high temperature GPC and solid-state 13C CP MAS NMR spectroscopy. Our results reveal that non-UV-stabilized LDPE degrades rapidly, showing extensive microcracking, molecular weight reduction, and formation of polar polymer defects within 600 hours. The addition of hindered amine light stabilizers (HALS) significantly delays these effects, yet their performance varies depending on the specific formulation. While Tinuvin 622 protects the polymer for about 2500 hours before sudden degradation and cracking occurs, Tinuvin 783 effectively prevents severe chain scission and large crack formation over the sampled 4000 hours of exposure. However, even with Tinuvin 783, fine surface microcracks still develop and cause the detachment of small microplastic particles. Ultimately, the most important finding is that even small amounts of additives have strong effects dictating not only the degradation kinetics but also the shape and chemical composition of the secondary microplastic particles formed by fragmentation.