Preparation and properties of toughened/flame‐retardant PA6/glass‐fiber composites reinforced by linear polyphosphazene elastomers

Abstract In this study, the challenges of brittleness and flammability in Polyamide 6/glass fiber (PA6/GF) composites, which are crucial for heat‐resistant and stress‐bearing structural parts, are addressed. Polyphosphazene (PZ) elastomers, known for their exceptional flame‐retardant properties, are introduced to enhance the robustness and safety of these composites. Specifically, poly(diaryloxy)phosphazene (PDAP) and poly(difluoroalkoxy)phosphazene (PDFP) are utilized, both contributing to the improved toughness and flame resistance of the PA6/GF composites. Experimental results show that PDAP mainly played the role of solid‐phase flame retardant, while PDFP mainly acted the role of gas‐phase flame retardant. For PA/PZs composites without adding GF, PDFP plays a more efficient flame retardant effect than PDAP. By introducing 15 Vol% of PDFP, the limiting oxygen index (LOI) of the composite reached 26.1%, while the notched impact strength increased by 297%. For PA/PZs/GF composites, PDAP plays a better flame retardant role than PDFP. Under the action of 30 vol% GF and 15 vol% PDAP, the LOI of PA6/PDAP/GF composite reached 26.8%, and the notch impact strength improved to 18.7 kJ/m 2 , which is 165% higher than that of PA6/GF, and the UL‐94 test reaches V‐0 level. The findings of the study highlight the potential of PDAP and PDFP to act as dual‐function modifiers. These modifiers can considerably ameliorate both the impact resistance and flame retardancy of PA6 and PA6/GF composites. Such dual enhancement surpasses the typical trade‐offs seen in conventional composites, indicating a constructive direction for future material innovation. Highlights Polyphosphazenes simultaneously enhance PA6's toughness & flame resistance. Distinct flame retardant mechanisms found in PDAP and PDFP. GF presence alters PDAP and PDFP's flame retardant efficacy. PDAP shows superior flame resistance in GF‐reinforced PA6 composites. Without GF, PDFP outperforms PDAP in enhancing flame retardancy.