Effect of Recycled Nylon and Phosphorus-Based Flame Retardant Content on the Thermal, Physical, and Flame Retardant Properties of Recycled Nylon Flame-retardant Composites

With the growing demand for sustainable engineering plastics, recycled nylon has attracted considerable attention as a high-value material for automotive and electrical/electronic applications. However, its inherent flammability and melt-dripping behavior necessitate the development of effective halogen-free flame-retardant systems, among which phosphorus-based flame retardants have emerged as promising alternatives due to their excellent flame-retardant performance achieved through combined gas-phase and condensed-phase mechanisms. This study investigates the effects of recycled nylon content, as well as the type and loading level of phosphorus-based flame retardants, on the thermal, mechanical, and flame-retardant properties of recycled nylon-based flame-retardant composites. The results demonstrated that increasing the flame retardant content generally lowered the thermal decomposition temperature, while promoting char formation, thereby improving the flame-retardant performance of the composites. In terms of mechanical properties, higher recycled nylon content resulted in an overall decrease in both tensile strength and impact strength, whereas PL900 exhibited relatively superior impact strength retention compared to the other flame retardants. Flame retardancy tests further revealed that the control sample without flame retardant showed a UL-94 V-2 rating, while most samples containing medium to high flame retardant loadings achieved the UL-94 V-0 rating. However, CEPPA-Al exhibited relatively limited effectiveness in achieving the V-0 rating even at high loading levels. These findings suggest that the type and loading level of flame retardants exert a complex influence on the physical properties and flame-retardant performance of recycled nylon-based composites, highlighting the importance of optimizing the composite formulation based on the desired performance requirements.