Degradation mechanisms in PBSAT nets immersed in seawater

Fishing gears are known to continue fishing after being abandoned, lost, or discarded through a phenomenon called ghost fishing. After this ghost fishing period, disintegrated nets contribute to plastic pollution. Biodegradable nets could be an alternative to conventional nets to reduce ghost fishing but must strike a delicate balance between durability and degradation. This study evaluates the seawater degradation of a net made of polybutylene(succinate-co-adipate-co-terepthalate) (PBSAT) at several scales: monofilament, knot, and net. Mechanical testing was used to monitor the strength at each scale during immersion at several temperatures: 4 °C, 15 °C, 25 °C, 40 °C. Steric exclusion chromatography (SEC), scanning electron microscopy (SEM) and X-ray tomography were used to investigate degradation processes. While no degradation was observed for samples immersed for 240 days at 4 °C, hydrolysis led to embrittlement at 40 °C. Biotic degradation was observed at both 15 °C and 25 °C with distinct degradation patterns and bacteria shapes. At both temperatures, the degradation was accelerated in the knot, leading to an unusable net after 240 days at 15 °C while no loss of strength was detected at the monofilament scale. These findings suggest that the durability of the knot is critical for successful development of a biodegradable polymer for application in gillnets.