Degradation Behavior of Biodegradable and Conventional Polymers for Gill Nets, Exposed to Accelerated Aging

Replacing nondegradable plastics in fishing gear with abrasion-resistant biodegradable polymers is expected to reduce marine pollution caused by seabed contact and to lower the environmental impact of abandoned, lost, or otherwise discarded fishing gear (ALDFG). The chemical and physical properties, as well as the tribological behavior of conventional polyamide (PA6) and biodegradable poly butylene succinate-co-adipate-co-terephthalate (PBSAT) monofilaments for a commonly used fishing gear (gill nets), treated under accelerated aging simulating outdoor conditions, have been studied. A plethora of different methods have been used to investigate the degradation mechanism, including scanning electron microscopy, optical microscopy, 3D imaging and wear measurements, nanoindentation, mechanical and tribological testing, ATR-FTIR analyses (including micro-ATR-FTIR microscopy), and ¹H NMR spectroscopy. FTIR data indicate alterations in the outermost monofilament layer, and NMR analysis corroborates that the aging effects initially take place at the surface. PA6 showed signs of chain cleavage, while PBSAT did not show any sign of degradation, indicating hydrolysis to small, dissolved molecules during aging. The findings revealed that for both PA6 and PBSAT, the process of aging exerts a small influence on the tensile modulus. After a thousand hours of aging, an increase in the tensile modulus was observed, amounting to 21% and 5%, respectively, for PA6 and PBSAT. However, a pronounced impact on the elongation at break was detected. The elongation at break diminished by approximately 67% and 91% for PA6 and PBSAT, respectively. Tribological testing of the monofilaments shows higher wear and abrasion of the PBSAT monofilament under dry conditions compared to PA6. Nevertheless, under conditions of lubrication by seawater, the wear and friction force exerted by PBSAT and PA6 were found to be comparable. This study demonstrates that biodegradable PBSAT materials can replace nondegradable PA6 in gill nets.