Effect of a novel intumescent retardant for ABS with synergist Al(H2PO2)3

Abstract

A novel intumescent flame retardant (IFR), containing ammonium polyphosphate (APP) and poly(hexamethylene terephthalamide) (PA6T), was prepared for acrylonitrile–butadiene–styrene (ABS). Limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA) were used to investigate the flammability property and thermal stability of the IFR/ABS systems. It was found that the flame retardancy of the IFR/ABS systems was improved significantly. When the components of the IFR were 25% APP and 5% PA6T, the LOI value of IFR/ABS system reached to the maximum of 29, but only UL-94V-1 rating was passed. Thus, Al(H2PO2)3 was incorporated into ABS/APP/PA6T system as a synergistic agent, it was found 2% addition of Al(H2PO2)3 caused PA6T/APP/PA6T/Al(H2PO2)3 (70/23.3/4.7/2) to pass V-0 rating of UL-94 test. Meanwhile, the TGA curves indicated that PA6T could be effective as a charring agent and there was a synergistic reaction between PA6T and APP, which effectively promoted the char formation of IFR/ABS composites. Moreover, the residual char obtained after the LOI test of the IFR/ABS was characterized by Fourier transform infrared spectra (FTIR). Results indicated that P–O–C chemical bond was formed in the residual char, which could indicate the cross-linking reaction between PA6T and APP could occur. Furthermore, scanning electron microscopy (SEM) was used to investigate the morphology of the residual char formed in the LOI tests. It was revealed that both ABS/APP/PA6T (70/25/5) and PA6T/APP/PA6T/Al(H2PO2)3 (70/23.3/4.7/2) formed uniform and compact intumescent charred layers.