Synergistic effect between a hyperbranched charring agent and ammonium polyphosphate on the intumescent flame retardance of acrylonitrile-butadiene-styrene polymer

A hyperbranched polyamine charring agent (HPCA) containing triazine was prepared by using 4,4′-oxybisbenzenamine and cyanuric trichloride through A2 + B3 approach. The structure and thermal stability of the product were characterized by Fourier transform infrared spectrometry (FT-IR), nuclear magnetic resonance spectrometry (1H NMR) and thermogravimetric analysis (TGA). It is shown that the carbonaceous residue at 700 °C is higher than 60 wt% suggesting a good char forming ability. Intumescent flame retarded acrylonitrile-butadiene-styrene (IFR-ABS) was prepared with HPCA and ammonium polyphosphate (APP) via melt blending. The flame retardance and thermal properties of the IFR-ABS were studied through limited oxygen index (LOI) and UL-94 vertical burning. The thermal degradation and char forming behaviour was tested with TGA and the morphology of char layer was observed by using scanning electron microscopy (SEM). The results show that a good synergistic effect is present between HPCA and APP. The calculated carbonaceous residue at 800 °C is 24.3 wt%, however the experimental value is 49.7 wt%, which is twice the former. Furthermore, the HPCA and APP have a promoting effect for char forming of IFR-ABS during combustion, for example, there is little carbonaceous residue for ABS at 550 °C according to TGA results in air, but there is 18.4 wt% carbonaceous residue for IFR-ABS with 25 wt% flame retardants. Moreover, the LOI for IFR-ABS is improved to 26.9 from 18.0 for ABS, and UL-94 V-0 rating is achieved with 30 wt% flame retardants.