Flame Retardant are substances that can be chemically inserted into the polymer molecule or be physically blended in polymers after polymerization to suppress, reduce, delay or modify the propagation of a flame through a plastic materials. There are several classes of flame retardants; Halogenated Hydrocarbons (Chlorine and Bromine containing compounds and reactive flame retardants), Inorganic flame retardants ( Boron compounds, Antimony oxides, Aluminium Hydroxide, molybdenum compounds, zinc and magnesium oxides ), Phosphorous containing compounds (Organic phosphate esters, phosphates, halogenated phosphorus compounds and inorganic phosphorus containing salts).
Zinc Borate is a boron-based fire retardant with a chemical composition of xZnOyB2O3zH2O. The most commonly used grade have following structure 2ZnO.3B2O3zH2.3,5H2O.
Zinc Borate can be used as a fire retardant in PVC, Polyolefins, Elastomers, Polyamides, Epoxy resins. In halogen-containing systems, Zinc Borate is used in conjunction with antimony oxide, while in halogen-free systems, it is normally used in conjunction with alumina trihydrate, magnesium hydroxide, or red phosphorus. In some particular application Zinc Borate can be used alone.
Zinc Borate act through :
- Zinc halide or zinc oxyhalide that accelerate the decomposition of halogen sources and promote char formation.
- by the B2O3 moiety released, a low melting glass, that can stabilize the char. B2O3 released can also promote the formation of ceramic formation in systems containing ATH or magnesium hydroxide.
- the endothermic, stepwise release of water that can promote the formation of foamy char.
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