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Designing for degradation: the importance of considering biotic and abiotic polymer degradation
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Sequential abiotic/biotic degradation testing framework showing standard methods underestimate polymer breakdown by up to twofold.
Considering the increasing global plastic demand, there is a critical need to gain insight into environmental processes that govern plastic degradation in order to inform novel design of sustainable polymers. Current biological degradation testing standards focus on formation of CO2 (i.e., mineralization) alone as a diagnostic, ultimately limiting identification of structure-degradation relationships in a timely fashion. This work developed a sequential abiotic (i.e., photodegradation and hydrolysis) and biotic degradation test and applied it to a suite of 18 polymers, including ten lab produced, novel polyhydroxyalkanoate polyesters, and eight commercially available, bio-based (i.e., polylactic acid and poly-3-hydroxybutyrate) and fossil-derived (i.e., polystyrene, polypropylene, low density polyethylene, poly(ethylene terephthalate) and tire rubber) polymers. Biomineralization alone following standard methods (i.e., ASTM 6691-17, ISO 23977-1 2020) underestimated polymer degradation up to two-fold over 28 days. Simulated sunlight enhanced the overall polymer degradation by mobilizing dissolved organic carbon (DOC). After photoirradiation, up to 100% of released dissolved organic carbon was bioavailable for marine microbes over 14 days. Photodegradation and hydrolysis could be explained by structural drivers in the commodity polymers, and the lab-synthesized polymers illustrated a limit to total degradation beyond which no enhancements in degradation were achieved. Taken together, this workflow allows for relatively fast experimental determination of environmentally relevant stimuli to help support eventual elucidation of structure-property relationships for enhanced a priori design of degradable polymers.
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Abiotic degradation and accelerated ageing of microplastics from biodegradable and recycled materials in artificial seawater
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Researchers examined the degradation behavior of microplastics from two biodegradable plastics (polylactic acid and Mater-Bi) and recycled PET under simulated seawater and photo-oxidative conditions. They identified hydrolysis as the primary degradation pathway and characterized the oligomers, degradation products, and plastic additives released into the water. The study improves understanding of how these alternative plastic materials break down in marine environments and what chemicals they release.
The fate of biodegradable polyesters in the marine environment
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Researchers tracked the degradation of five biodegradable plastics in simulated marine environments over nearly a year, including materials like polylactic acid and polyhydroxybutyrate. While all materials showed signs of degradation such as surface cracking and weight loss from hydrolysis, they also released polymer fragments into surrounding sand, indicating that even biodegradable plastics can generate microplastic pollution. The findings suggest that labeling a plastic as biodegradable does not guarantee it will fully break down in ocean conditions.
Aging dynamics and subsequent dissolved organic matter evolution of microplastics regulated by UV-salinity conditions.
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A lab study exposed common plastics (polyethylene, polypropylene) and a biodegradable plastic (polylactic acid) to sunlight-like UV and different salt levels for 60 days. UV light caused more breakdown in all plastics, and higher salinity worsened this for the conventional plastics, while the biodegradable plastic broke down through a different process and released more dissolved material.
Photodegradationof Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)and Its Effects on Marine Biodegradability
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Researchers examined the photodegradation dynamics of the biodegradable polymer PHBH under simulated UV conditions and assessed the effects on its marine biodegradability. UV weathering altered PHBH's surface properties and modified its degradation rate in marine environments, raising questions about the environmental safety claims for this material.
Photodegradation of Poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) and Its Effects on Marine Biodegradability
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Researchers investigated the photodegradation of the biodegradable polymer PHBH under accelerated UV exposure and tested whether photodegradation affected its marine biodegradability. They found that UV exposure degraded PHBH's surface and altered its biodegradation rate in seawater, suggesting that environmental weathering affects this supposedly ocean-safe material.
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