High flame retardant PVC sheath compound for power cable (2)

High flame retardant PVC sheath compound for power cable (2)


2.1.2 Effects of different amounts of antimony trioxide and ammonium octadromolybdate on material properties  

Antimony flame retardants have always been effective flame retardants of polymer and occupy an important position in the development of flame retardancy of polymer materials, especially when Sb2O3 synergy with halogen flame retardant, it could achieve effective flame retardancy. PVC as commonly used sheath material, the Chloridion of PVC could synergy with Sb2O3. And study shows when adding 5-10phr Sb2O3 could has excellent flame retardant properties. But the smoke release of halogen-antimony system is high, can not meet smoke suppression requirement.

At present, as the most effective smoke suppressant in PVC materials, molybdenum compounds are widely used in low smoke PVC materials. Compared with Sb2O3, molybdenum series compounds have better flame retardant and smoke elimination effect, and some studies show that it plays a role in the condensed phase, and has a very effective role in the flame retardant shell forming of PVC materials.  

Chart 3 Influence of different antimony trioxide amount on material properties

Sb2O3Tensile strength (MPa)Elongation at break (%)Oxygen Index (%)Density (g/cm3)

Chart 4 Influence of different AOM amount on material properties

AOMTensile strength (MPa)Elongation at break (%)Oxygen Index (%)Density (g/cm3)

From chart 3 we can see that the tensile strength and elongation at break of PVC compound has no clear decrease when adding 21phr Sb2O3, and when adding 9phr Sb2O3, the oxygen index of PVC compound reaches 29%, and then the increase variation is small when continuing adding Sb2O3. At the same time, along with the proportion of Sb2O3, the density of PVC compound increases, so when design power cable, the content of Sb2O3 should not be excessive.

From chart 4 we can see that the tensile strength and elongation at break of PVC compound has no clear decrease when

adding AOM. The performance is similar with adding Sb2O3.

2.1.3 Influence of different amount of zinc botate and zinc stannate amount on material properties

Zinc series flame retardant is also widely used in PVC compound as lame retardant, especially zinc borate, zinc stannate. Zinc borate hydrate compound will release crystal water at 290~450℃. Zinc borate has the advantages of cost effective, low specific gravity, halogen-free and non-toxic. In the polymer combustion, zinc borate can form glass inorganic expansion coating, through the formation of borate ester salt, to promote the surface of the polymer carbonization, then form an effective oxygen isolation layer, with shell oxygen isolation effect, effectively inhibit the combustion and smoke of PVC materials. Zinc stannate is often used as a smoke suppressant in PVC. It has a synergistic effect with the halogen of PVC material itself. Its flame retardant mechanism is similar to zinc borate, and it has better smoke suppression effect.  

It can be seen from the experiment that the tensile strength and elongation at break of PVC material do not change obviously when the zinc borate is 12phr. The tensile strength and elongation at break of PVC materials decreased to a certain extent when the amount of zinc borate was increased. At the same time, it can be seen from the change of oxygen index of PVC material that zinc borate material can improve the oxygen index of PVC, but when the amount is greater than 12, the oxygen index of PVC material does not increase significantly. In addition, the effect of zinc stannate on mechanical properties of PVC material is consistent with that of zinc borate. What’s different is that the oxygen index is keeping increase with the adding of zinc stannate.

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