Internal Structure Dependence of Biodegradation for Polyamide 4 Thin Films in Seawater.

Recently, polyamides have been widely used in various fields due to their excellent durability, thermal stability, and other advantageous properties. However, polyamide products that end up in oceans have become a source of microplastics. For this reason, the development of highly degradable polyamides is greatly desired. We here focused on polyamide 4 (PA4), which has a high density of amide groups in its main chain. As model samples, two types of PA4 thin film, thermally annealed at different temperatures, were prepared, and their aggregation states and biodegradation behavior were examined. The results revealed that the swelling properties of the PA4 thin films in underwater environments play a crucial role in their degradation. It was also found that the crystal polymorph of the PA4 thin films significantly influences their biodegradation behavior. This fundamental understanding of PA4 degradation behavior will contribute to the further development of PA4-based devices.