Synergistic effects of resorcinol bis (diphenyl phosphate) (RDP) on the flame retardancy, foaming behavior, and thermal stability of poly (2,6-dimethyl-1,4-phenylene oxide) / polyamide (PPO/PA) composites

This study explores the modification and foaming behavior of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) and polyamide 6 (PA6) composites with resorcinol bis (diphenyl phosphate) (RDP) as the flame retardant. The composites were prepared by extrusion blending, followed by chemical foaming injection molding. The effects of RDP content and core-back distance on microstructure, thermal properties, rheological behavior, flame retardancy, and foaming performance were systematically evaluated. RDP improved the flame retardancy by forming a dense protective char layer, but simultaneously reduced the thermal stability and crystallinity due to its plasticizing effect. Notably, incorporation of RDP improved the foaming quality, producing a more uniform cellular structure with smaller cell size. Rheological analysis indicated that an increase in RDP content reduced the melt viscosity and elasticity, thus promoting superior foam formation. The foamed structure could reduce the LOI value slightly, compared to un-foamed samples, but the overall flame retardancy remained high. At 8% RDP loading, the average cell diameter reached 87 μm, and the cell density increased to 5.3×10 5 cells/cm 3 . This shows the synergistic effects of RDP on the flame retardancy and foaming performance of the composites. These findings underscore the potential of PPO/PA6 composites for applications demanding lightweight materials with enhanced fire safety. • The high flame-retardant and lightweight PPO/PA composites were prepared. • RDP enhances both the flame retardancy and foaming performance of PPO/PA6 composites through its collaborative efficiency. • RDP improves the processability and enhances the thermal stability of the PPO/PA6 composites.