Synergistic effect of graphitic carbon nitride and ammonium polyphosphate on the enhanced flame retardant and smoke suppression properties of biobased polyamide 56

Abstract Seeking a facile strategy to synthesize efficient and inexpensive flame retardant which endows biobased polyamide 56 (PA56) with desirable flame retardancy is an urgent need. Here, ammonium polyphosphate (APP) was modified with graphitic carbon nitride (g‐C 3 N 4 ) to synthesize a nitrogen‐phosphorus flame retardant (CN@APP) and then applied in biobased PA56. The X‐ray diffraction (XRD) and Fourier transform infrared (FT‐IR) spectra demonstrated that APP was successfully microencapsulated with g‐C 3 N 4 . The micromorphology structure was further characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PA56/CN@APP attained a UL 94 V‐0 rating and limiting oxygen index (LOI) value of 31.7%. A sharp reduction of 35.3% in peak heat release rate (pHRR) and 24.0% in total heat release (THR) and an 874% increase in char yield were noticed for PA56/CN@APP2 compared with pure PA56. Additionally, the peak smoke production rate (pSPR) and total smoke production (TSP) of PA56/CN@APP2 were 33.0% and 21.8% lower than those of pure PA56. Scanning electron microscopy (SEM), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy were employed to analyze the condensed phase residues from the cone calorimeter test (CCT). The results indicated that CN@APP was beneficial for forming a more stable and compact carbon layer during combustion, thereby insulating the heat transfer and improving the flame retardancy and smoke suppression of PA56.