Flame Retardancy via in-Mould Coating and Durability of Flame Retardants After Mechanical Recycling in all-polyamide Composites Prepared by In Situ Polymerisation

Sustainable development requires that the structural materials can be easily recycled. The advantage of all-polyamide composites (APCs) is that the matrix and the reinforcing material come from the same material family and can be easily mechanically recycled. In the research, polyamide 6.6 (PA6.6) reinforced polyamide 6 (PA6) composites by anionic ring-opening polymerisation are prepared and created a flame retardant coating on their surface by in-mould coating. The thermal stability of the created flame retarded APCs is investigated by thermogravimetric analysis (TGA), and the flammability is tested by UL-94 test, limiting oxygen index (LOI) and mass loss type cone calorimetry (MLC). The coatings reduced the peak heat release rate (pHRR) by up to 49% and increased the residual mass after combustion. The flame retarded APCs are mechanically recycled with the addition of 50 mass% primary material, and their thermal properties and flammability are investigated. The most effective formulations fully preserved their ability to reduce pHRR, demonstrating the durability of flame retardant properties through multiple life cycles. In the case of the sample containing 3% phosphorus from hexaphenoxycyclotriphosphazene (HPCTP) and 4% expandable graphite (EG), the pHRR after recycling is reduced by 35% compared to primary APC without flame retardants.