Marine-Biodegradable Polyamide 4/6 Copolymer Fibers

Mismanaged fishing gear significantly contributes to marine plastic pollution and ghost fishing. Marine biodegradable polyamide 4/6 (PA4/6) random copolymers containing 66, 87, and 93 mol % PA6 were synthesized in this study via bulk ring-opening polymerization to combine processability and environmental degradability. Differential scanning calorimetry and thermogravimetric analyses revealed that copolymerization reduces the melting temperatures (Tm) of PA4 and PA6 while maintaining a thermal decomposition temperature considerably above Tm, enabling a wide processing window. Fishing-line-grade fibers fabricated from these copolymers exhibited mechanical properties comparable to those of commercial PA6 lines, with the fracture stress increasing with an increasing PA6 content. Photooxidative aging under accelerated ultraviolet (UV) light exposure demonstrated that the incorporation of PA4, as compared to PA6, enhances UV resistance. Biodegradation tests in extracted seawater demonstrated that the biodegradability increases with an increasing PA4 content. Notably, all copolymer fibers became biodegradable after UV exposure. These results indicate that PA4/6 copolymers are promising candidates for high-performance biodegradable fishing gear and offer a viable alternative to persistent PA6, polyethylene terephthalate, and poly(vinylidene fluoride) fishing lines in marine environments.