Combustion Characteristics Of Hydrotalcite/zinc Compouds Modified Poly(vinyl Chloride)

Poly(vinyl chloride) (PVC) is a widely used plastic due to its fire and corrosion resistances, good mechanical properties and low production cost. But PVC also has disadvantages of poor thermal stability, producing of a lot of heat, smoke and toxic chemicals during its combustion. Hydrotalcite (HT) is a new fire and smoke retardant for PVC. In this thesis, PVC resins modified by HT, HT/ZnO, HT/Zn3(PO4)2 and HT/Zn2SnO4 were prepared by in-situ suspension polymerization of vinyl chloride (VC), and the influences of the composition and added amount of inorganic fire and smoke retardants on the combustion characteristics of modified PVC composites were measured by using cone calorimeter and smoke density analyzer.At first, PVC composite resins with acceptable particle size and morphology were prepared by in-situ suspension polymerization of VC in the presence of inorganic with a maximum content of 10wt% (to VC mass). TEM analysis showed that HT and other inorganic particles were dispersed well in PVC matrix. Smoke density analysis showed that HT with smaller dispersion size exhibited better smoke retardant effect to PVC. The maximum smoke densities of PVC composites were decreased 56.9% and 59.2%, when 1 wt% (to VC mass) 2# and 3# HT were added in the polymerization system under the non-fire combustion mode.Secondly, the combustion characteristics of unplasticized PVC modified by HT/ZnO, HT/ZnO/MgO and HT/Zn3(PO4)2 were analyzed by using the cone calorimeter. It is found that the fire and smoke retardant efficiencies of HT/ZnO to PVC were increased as the amount of added HT and ZnO increased. The peak heat release rate (pk-HRR), peak smoke production rate (pk-SPR) and CO production (COP) of PVC composite were decreased 50%,39% and 41%, respectively, when 2wt% HT and 2wt% ZnO (to VC) were added. The HT/Zn3(PO4)2 composite also had good fire and smoke retardant effect to PVC. The pk-HRR, total heat release and average heat release were decreased more than 50%, and pk-SPR and COP were decreased 38% and 50%, respectively, when 1 wt% HT and 1 wt% Zn3(PO4)2(to VC) were added. The addition of HT and zinc compounds would be favor to the formation of carbon.Finally, the influences of HT and zinc stannate composite on the limited oxygen index (LOI) and smoke density of plasticized PVC were investigated. It was found that the addition of dioctyl (o-)phthalate (DOP) plasticizer would significantly increase the smoke density of PVC. The HT/Zn2SnO4 composite had a particular fire and smoke retardant effect to PVC. The LOIs of modified PVC with 3wt% HT and 3wt% Zn2SnO4 were 33.5%,28.6% and 26.2%, and smoke densities were 172.4,195.8 and 252.5, respectively, when 30phr,40phr and 50phr DOP were added. Compared with PVC with no HT and Zn2SnO4, the smoke densities were decreased 47%, 42% and 34% for PVC with 3Ophr,40phr and 5Ophr DOP.The obtained results would instruct the preparation of PVC composites with excellent fire and smoke retardancy.