A novel intumescent flame retardant and smoke suppression system for flexible PVC

Triazine derivatives containing a hydroxystannate or zinc hydroxystannate (ZHS) group were synthesized as a novel intumescent flame retardant (IFR) and smoke suppressant for flexible PVC, and their structure and thermal stability were evaluated by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), respectively. Limiting oxygen index (LOI) and smoke density rating (SDR) tests demonstrated that melamine hydroxystannate (MASN) and a composite of MASN and ZHS (MAZSN) are effective flame retardants and smoke suppressants for flexible PVC at levels of 5-30 parts per hundred parts of base resin (phr). The thermal degradation of the flame-retardant flexible PVC was investigated by TGA, differential thermal analysis (DTA), and scanning electron microscopy (SEM). The results showed that adding MASN and MAZSN not only decreased the initial decomposition temperature and increased the weight loss rate at the first stage, but also promoted char formation and expansion at the second stage. Moreover, flame retardants consisting of MASN or MAZSN and the PVC matrix form a novel IFR and smoke suppression system, in which the PVC matrix acts as the carbonization agent and Sn(OH)(6)(2-) and Zn(2+) provide the acid (Lewis acid). When combustion occurs, Sn(OH)(6)(2-) and Zn(2+) catalyze dehydrochlorination and promote early crosslinking of PVC, and hydrogen chloride and melamine (MA), acting as the blowing agent, enhance the intumescence of the char. Copyright (C) 2011 John Wiley & Sons, Ltd.