Zinc Borate is a multifunctional boron-based fire retardant with the chemical composition xZnO.yB₂O₃.zH₂O. The company who was successful firstly to R & D is USA Borax Company, and registered brand Firebrake ZB. According to the formulation, there were decades of types product. 2ZnO 3B₂O₃ 3.5H₂O was normal formulation, in which contain 3.5 crystal hydrate, molecule weight is 434.68, it was called ZB2335 also.

Zinc borate is white crystal powder, insoluble in water, but little soluble in hot water and dilute acid. The solubility in NaOH solution is very little, but good in strong alkali and its solution. The oil absorption is 35/100g. Zinc borate will loss crystal hydrate over 300.

 

Flame retardant mechanism

 

1. When the temperature is over 300, Zinc Borate will release crystal hydrate to absorb lots of thermal energy and decline the temperature of char.

2. The released water will dilute O₂ content in the air, which will suppress combustion reaction obviously.

3. In the last, glassy layer of B₂O₃ will be produced to cover the polymer, which could be thermal insulation and oxygen prohibition.

4. If Mixed with other organic halogenide, Zinc Borate will decompose and react with halogen to produce ZnX₂ZnXH₃BO₃(XC1Br) that will cover the surface of char and prohibit the air. Additionally, during the combustion of BX₃, released HX will catalyze to prohibit the chain reaction between high active free radical, so there will be much better flame retardant effect than completely single flame retardant material.