Novel polyamide 6 composites based on Schiff-base containing phosphonate oligomer: High flame retardancy, great processability and mechanical property

Conventional methods of improving the flame retardancy of PA 6 usually involve the sacrifice of mechanical properties, which is unfavorable for the practical application. Herein, two Schiff-base containing phosphonate oligomers PSA and POSC, were designed and used as novel flame retardants for PA 6. The PA 6-PSA20 composite involving P-Ph structure achieved a LOI value of 27% and UL-94 V-0 rating, while the PA 6-POSC20 composite involving P-O-Ph structure achieved a higher LOI value of 32% but a UL-94 V-2 rating. The PA 6-POSC composites also exhibited better heat-suppression effect than the PA 6-PSA composites. The different flame-retardant mechanism of these two flame retardants were comprehensively studied via Raman spectra, XPS, FTIR, TG-IR and Py-GC/MS. Additionally, the PA 6 composites all exhibited great processability and largely retained mechanical properties. This work proposed an efficient route for preparing flame-retardant polyamide composite with excellent overall performance.