Intumescent flame retardant-montmorillonite synergism in ABS nanocomposites

A synergistic effect was observed between montmorillonite and a novel intumescent flame retardant, poly (4, 4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) in ABS nanocomposites. Montmorillonite dispersion was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal stability and flammability properties were investigated by thermogravimetric analysis (TGA) and cone calorimeter tests. Incorporating PDSPB together with montmorillonite enhanced thermal stability and flame retardancy of the ABS resin. The synergistic mechanism is caused by formation of silicoaluminophosphate (SAPO) structure formed by reactions between the phosphoric acid generated on heating from PDSPB and montmorillonite. Decomposition of the alkylammonium ion yields strongly acidic catalytic sites that may promote the oxidative dehydrogenation crosslinking charring process and increase the char yield. Silicoaluminophosphate was characterized by FT-IR spectrometry and field emission scanning electron microscopy.