Understanding the degradation of bio-based polymers across contrasting marine environments using complementary analytical techniques

Biodegradable and compostable polymers have emerged as an alternative to conventional plastics to mitigate environmental problems related to plastic perdurability. However, these materials are certified as biodegradable/compostable following technical standards that consider a limited range of environmental conditions. Therefore, some materials may not degrade as rapidly as expected under certain natural conditions. Understanding degradation patterns of polymers across diverse environments is essential to ensure their sustainable use. We examined the degradation of bio-based materials certified as biodegradable/compostable under various marine conditions, including the seabed and both the euphotic and aphotic zones of the water column, for one year through a comprehensive analytical approach combining weight loss measurements, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Despite the marked different degradation rate between materials, both lost five times more weight in sediment than in the water column, highlighting the influence of environmental compartment on degradation. Although light did not contribute to weight loss, it promoted molecular degradation by modifying chemical structures and thermal properties. Degradation was influenced by material-specific characteristics, with polymers of higher hydrophilicity and lower crystallinity being more prone to degradation. This was evidenced by changes in analytically derived parameters, including shifts in FTIR indices and reductions in maximum degradation temperature, activation energy and crystallinity, highlighting the complementary insights provided by the applied techniques. These findings provide an integrated understanding of degradation processes, supporting the design of more sustainable materials, and contributing to the development of new technical standards that better reflect natural conditions.