Low‐melting sulfate glasses as additives to semirigid PVC and their flame retardant and smoke suppressant properties

The role of low‐melting sulfate glasses (LMSG) as additives on the flame retardant and smoke suppressant properties of semirigid poly(vinyl chloride) (PVC), as well as the mechanism for flame retardancy and smoke suppression, were studied through the Limiting Oxygen Index (LOI) test. Smoke Density Rating (SDR) test, DTA‐TG, and SEM. The results show that the LMSG have good smoke suppressant properties. When the PVC compound contains 40 parts of LMSG, the SDR value will be reduced by about 45%. The Cu²⁺, Zn²⁺, Mn²⁺, and Ni²⁺ sulfates, as well as MoO₃, cause PVC to crosslink and form char, and the melt can protect not only the char formed during combustion and thermal degradation, but also undecomposed polymer. That is the main mechanism for flame retardation and smoke suppression when the additives melt. The mechanical properties of the PVC compounds containing different levels of LMSG were also studied.