Enhancement of a hyperbranched charring and foaming agent on flame retardancy of polyamide 6

A hyperbranched polyamine was prepared using an A(2)+B(3) approach. It acted as a hyperbranched charring and foaming agent (HCFA) in combination with ammonium polyphosphate (APP) to form a new intumescent flame retardant (IFR) system for polyamide 6 (PA6). Effect of HCFA on flame retardant and thermal degradation properties of IFR-PA6 was investigated by limiting oxygen index (LOI), UL-94 vertical burning, cone calorimeter, and thermogravimetric analysis (TGA) tests. The IFR system presented the most effective flame retardancy in PA6 when the weight ratio of APP to HCFA was 2:1. The LOI value of IFR-PA6 could reach 36.5 with V-0 rating when the IFR loading was 30 wt%. Even if the loading decreased to 25 wt%, IFR-PA6 could still maintain V-0 rating with an LOI value of 31. TGA curves indicated that APP would interact with both PA6 and HCFA in PA6/APP/HCFA composite under heating. The interaction between APP and HCFA improved the char formation ability of IFR system and then much more char was formed for PA6/APP/HCFA composite than for PA6/APP. Therefore, better flame retardancy was achieved. Moreover, the structure and morphology of char residue were studied by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results indicated that compact and foaming char layer containing P-O-C structure was formed for PA6/APP/HCFA system during combustion. Copyright (C) 2010 John Wiley & Sons, Ltd.