Effect of single-and double-layer encapsulated ZnSnO₃ on flame retardancy and smoke suppression properties of poly(vinyl chloride) membrane composites

The influence of single layer ZnSnO₃@Mg(OH)₂ microcapsule and double layer ZnSnO₃@Mg(OH)₂@melamine formaldehyde resin(MF) microcapsule on the flame retardancy and smoke suppression properties of polyvinyl chloride(PVC) membranes were analyzed by limiting oxygen index(LOI), horizontal and vertical burning test, smoke density(SDR) test, SEM and TG instrument. The results show that ZnSnO₃@Mg(OH)₂ and ZnSnO₃@Mg(OH)₂@MF_m icrocapsules can effectively enhance the flame retardancy, smoke suppression, anti-dripping and self-extinguishing properties of PVC membranes. The LOI value of ZnSnO₃@Mg(OH)₂/PVC and ZnSnO₃@Mg(OH)₂@MF/PVC membrane composites obviously increases, with increasing the content of the microcapsules. However, when the content of the microcapsules increases, the smoke density and self-extinguishing time of ZnSnO₃@Mg(OH)₂/PVC and ZnSnO₃@Mg(OH)₂@MF/PVC membrane composites decreases. The TG results show that the initial degradation temperature of ZnSnO₃@Mg(OH)₂/PVC and ZnSnO₃@Mg(OH)₂@MF/PVC membrane composites move to low temperature and the amount of residual carbon increases with the content of the microcapsules. The SEM micrographs of residual carbon of ZnSnO₃@Mg(OH)₂/PVC and ZnSnO₃@Mg(OH)₂@MF/PVC membrane composites show that the addition of the microcapsules effectively promotes the form compact carbon layer of ZnSnO₃@Mg(OH)₂/PVC and ZnSnO₃@Mg(OH)₂@MF/PVC membrane composites during burning, which not only can inhibit oxygen and heat to go into the PVC bulk, but also inhibit combustion gases to go out the PVC bulk. SEM and tensile strength results show that double layer microcapsule can availably improve the dispersion and compatibility between inorganic particles and PVC matrix.