Identifying the Polymer Content and Valorizing Waste Fishing Nets from Greek Coasts via Pyrolysis

Discarded fishing gear accumulating in marine and coastal environments poses a significant threat to marine ecosystems, particularly in Mediterranean countries such as Greece, and is increasing at an alarming rate. Therefore, sustainable management and recycling strategies for abandoned fishing gear and waste fishing nets (WFNs) are urgently needed. This study investigates pyrolysis as a sustainable valorization approach for WFN. A critical first step involves identifying the polymeric composition of the collected nets. For this purpose, a comparative assessment of polymer identification characterization methods was performed on twelve visually distinct WFN samples, employing Fourier Transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC), followed by GC/MS analysis of the pyrolysis products. According to the results, the WFN samples were identified as HDPE, PP, PA-6 and PA-6,6. Subsequently, the suitability of pyrolysis as a valorization strategy for WFN was evaluated in relation to the polymeric composition of the samples, using a laboratory-scale pyrolysis reactor. Pyrolysis of PA-6-based WFNs yielded more than 91 wt.% liquid products, with a high relative abundance of ε-caprolactam (51.6–61.8% r.a.), indicating strong potential for monomer recovery and further development toward closed-loop recycling. In contrast, pyrolysis proved less promising for the valorization of PA-6,6-based WFNs. Polyolefin-based WFNs yielded more than 88 wt.% hydrocarbon-rich liquid products, with potential valorization as fuel precursors.