Two series of inorganic melamine salts as flame retardants and smoke suppressants for flexible PVC

Two series of inorganic melamine salts containing a tungstate or molybdate were synthesized as a flame retardant and smoke suppressant for flexible PVC, and their flame retardancy and smoke suppression were studied by limiting oxygen index (LOI), smoke density rating (SDR) test, cone calorimeter, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). It can be found that the presence of melamine tungstate or melamine molybdate causes an obvious increase in LOI and a decrease in SDR. The cone calorimeter results reveal that melamine tungstate or melamine molybdate can clearly change the decomposition behavior of PVC and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate, smoke production rate, total smoke production, and so on. The TGA and SEM results demonstrate that melamine tungstate can delay the degradation of PVC and improve the stability of the char residue. Moreover, melamine molybdate and the PVC matrix form a novel intumescent flame retardant and smoke suppression system, in which the PVC matrix acts as the carbonization agent and molybdate as the acid source (Lewis acid). Molybdate can catalyze the dehydrochlorination reaction and promote the crosslinking reaction of PVC effectively. Melamine (MA) and the released hydrogen chloride can act as the blowing agent, which enhance the intumescence of the char. POLYM. COMPOS., 39:529–536, 2018. © 2016 Society of Plastics Engineers