Degradation and mechanical behaviour of rotationally moulded PLA and PE components in marine environment

Plastic pollution in oceans and marine environments is increasing, generating significant negative effects due to the widespread use of non-biodegradable polymers in marine applications such as buoys, sensors, covers, boat components, and various accessories, which often end up as marine litter. Polylactic acid (PLA), a well-known biodegradable and bio-based polymer, is increasingly being considered as a sustainable alternative to conventional plastics. However, while the marine degradation of PLA has been investigated in injection-moulded parts, films, and additively manufactured components, it remains largely unexplored in rotationally moulded structures, despite the fact that this processing method induces significant differences in material properties. In this work, PLA samples were manufactured using rotational moulding, a common method for producing hollow plastic parts, and later exposed to real marine conditions for 18 months. Samples were extracted every three months to assess weight loss, mechanical properties, thermal stability, and hydrophobicity, and results were compared with polyethylene (PE) controls. After 18 months, the material largely retained its mechanical properties and thermal stability, exhibiting a weight loss of approximately 1.3%, while hydrophobicity increased by nearly 40%, in line with expected hydrolytic degradation processes. Although further research is required, PLA may not entirely prevent long-term marine litter due to its low degradation rate in the marine environment; however, appropriate design and manufacturing strategies could enable controlled degradation.