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Influence of knot strength on the mechanical performance of a biodegradable gillnet
Summary
Researchers compared conventional nylon (PA6) gillnets to biodegradable alternative nets and found the biodegradable material lost even more strength at knots than expected from its weaker base fiber, making it less suitable as a direct replacement. Developing effective biodegradable fishing gear is important because lost or abandoned plastic nets — called ghost gear — are a major source of marine microplastic pollution.
Ghost fishing is a global issue that can be addressed using fishing gear materials that do not persist in the marine environment. However, for these alternatives to be widely adopted, they must meet the same mechanical specifications as current commercial materials while degrading without any negative impact. The objective of this study was to compare a conventional gillnet made of polyamide 6 (PA6) with an alternative made of poly(butylene succinate-co-adipate-co-terephthalate) (PBSAT) at three different scales: monofilament, knot, and net. While the PBSAT monofilament's strength was half that of the conventional PA6 net, knot and net losses were even more significant. This indicates a greater sensitivity of the material to the knot. Since the results between the knot and net scales were coherent, testing whole net panels is not necessary. Studying the curvature and the behaviour of the knot revealed its complex geometry and mechanical behaviour. Testing the weaver's knot is a good indicator for studying the relevance of an alternative to conventional fishing gear materials. This should be considered when developing biodegradable nets in order to reduce ghost fishing at sea.