Effect of soft segment chemistry on marine-biodegradation of segmented polyurethane elastomers

Marine plastic pollution is a critical global concern with widespread ecological impacts. Among the various types of plastic waste, polyurethane (PU), a versatile polymer used in numerous applications, contributes significantly to marine pollution, posing unique challenges for degradation and potential toxic effects on marine organisms and ecosystems. To eliminate natural PU waste, the process of PU biodegradation must be properly understood. In this study, we investigated the biodegradation of three segmented polyurethane (SPU) elastomer films with various soft segment (SS) structures in extracted seawater. Degradation tests revealed that polycaprolactone (PCL) - based SPU exhibited the highest biodegradability when exposed to extracted seawater. In contrast, poly(tetramethylene ether)glycol (PTMG) - based- and polybutylene adipate (PBA) - based SPU showed minimal biodegradability in the extracted seawater. Two marine bacterial strains that are closely related to Halopseudomonas gallaeciensis and Halopseudomonas pachastrellae species, which demonstrate a capacity for biodegrading PCL-based SPU, were isolated. Synchrotron radiation X-ray scattering (WAXS/SAXS) revealed that biodegradation predominantly occurred within the SS phase comprising the PCL chains of the SPU film, while the hard segment (HS) was intact after the 4-week biodegradation test. Consequently, careful consideration of the ratio between the hard segment (trans-1,4-bis(isocyanatomethyl)cyclohexane and 1,4-butanediol) and the PCL components is essential for minimizing the residual of the hard segment in nano- or microplastic forms in the ecosystem, given its inherent stability under environmental conditions.