Fabrication and thermal stability studies of polyamide 66 containing triaryl phosphine oxide

An intrinsically halogen-free flame retardant polyamide 66 (FR-PA66) was fabricated successfully by two-step polymerization reaction with adipic acid hexamethylene salt (AH salt) and bis(4-carboxyphenyl) phenyl phosphine oxide (BCPPO) as raw materials. The structure, combustion properties and thermal stability were characterized by means of intrinsic viscosity, Fourier transform infrared spectroscopy (FTIR), combustion testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and scanning electron microscope (SEM). Experiments show that BCPPO have excellent copolymerization properties with AH salt. And incorporation of triaryl phosphine oxide (TPO) did not transform the crystal phase structure of PA66. During fabrication of FR-PA66, melt polymerization time exhibits more surprising influence on intrinsic viscosity than aqueous solution polymerization time. The LOI value of FR-PA66 with 9 wt% TPO reaches 27·2, and corresponding UL94 rating reaches V-0. Improved thermo-stability of FR-PA66 can be attributed to both forming of compact char protective layer and further consolidation effect of P/N synergistic system.