Composite materials for automotive applications based on recycled fishing nets and biochar

Discarded fishing nets constitute a significant part of ocean pollutants (640,000 tonnes/year), accounting for 20 % of all marine activities. Giving new economic value to end-of-life fishing nets could encourage their recovery through an appropriate logistical collection system. Their reuse as raw material can reduce marine pollution and the use of petro-based plastics, particularly in the automotive sector. In this context, the present study aims to explore the recyclability of disposed fishing nets to produce more sustainable composites, using epoxidized waste vegetable oil (EWVO) as a biocompatible material. Furthermore, rice husk biochar (BC) is used as a renewable alternative to traditional carbon black due to its multifunctional characteristics as a flame retardant. EWVO was synthesized by epoxidation of Repurpose Used Cooking Oil (RUCO) and BC was produced by pyrolysis of rice-husk. Fishing nets were collected, washed, air-dried, and characterized by FTIR and DSC analyses. Thermal analyses were performed to assess the materials' suitability for subsequent mechanical recycling and compounding by melt extrusion. The composites were produced by a single-screw extruder at 235-240°C (60 rpm, N2 atmosphere) using different EWVO and BC amounts. Rheological analyses and tensile testing were conducted to evaluate material processability and mechanical performance compared to virgin plastics. Flame retardant characteristics of developed composites were evaluated through cono-calorimetric measurements and vertical burn tests. The analyses conducted resulted in the identification of HDPE, polyamide 6, and polyamide 6,6 as the constituents of the gathered nets, with polyamide 6 being the predominant material. Each net was successfully reprocessed by extrusion, exhibiting similar mechanical properties to the virgin plastics. Preliminary compatibilization tests for HDPE/PA6 blends using EWVO showed that for HDPE/PA6 75/25 and 85/15 blends, the addition of EWVO at 2 phr had a satisfactory compatibilizing effect. The epoxy groups of EWVO reacted during blending with both PA6 carboxyl and amino terminal groups, resulting in oil-terminated PA6. These molecules migrate to the PA6/HDPE interphase, thereby reducing interfacial tension and improving compatibility between the polar polyamide and the hydrophobic polyethylene. This resulted in a material with improved mechanical properties compared to the blend without compatibiliser. Composites based on recycled PA6-based fishing nets, containing 5, 10, 15, and 20 wt.% of BC, were successfully processed by extrusion. The incorporation of BC increased Young's Modulus and stress at break of PA-6 but reduced strain at break. Furthermore, preliminary cone calorimetric measurements suggest the tendency of rice husk biochar, markedly rich in silica, to induce flame retardant properties.