Afterglow suppressant, zinc borate

Zinc Borate as a Flame Retardant, Smoke Suppressant, and Afterglow Suppressant in Polymers... 

Zinc Borate (2Zn0-3B203-3.5H20) is a unique multifuntional fire retardant. It can function as a flame retardant, smoke suppressant, afterglow suppressant, as well as an anti-tracking agent in polymers. It has been used extnesively as a fire retardant in PVC, polyolefin, nylon, polyester, epoxy, acrylic, urethane, rubbers, etc. 

AS AN AFTERGLOW SUPPRESSANT. Due to its unique glass-forming ability (i.e., from the B203 moiety), the zinc borate can also function as an afterglow suppressant as illustrated in Table... 

In halogen-containing polymers, the multifunctional zinc borate can function as a flame retardant, smoke suppressant, and afterglow suppressant. 

Polyolefins When used in conjunction with a halogen-based flame retardant, this zinc borate can partially replace antimony oxide (30%-40%) and still maintain the same fire test performance. In addition, it can improve aged elongation properties, increase char formation, and decrease smoke generation. The B203 moiety in zinc borate can also provide afterglow suppression (Table 9.6). 

Zinc borates are predominately a condensed phase fire retardant. In a halogenated system such as flexible PVC, it is known to markedly increase the amount of char formed during polymer combustion whereas the addition of antimony trioxide, a vapor-phase flame retardant, has little effect on char formation. Analyses of the char show that about 80%-95% of the antimony is volatilized, whereas the majority of the boron and zinc from Firebrake ZB remains in the char (80% and 60%, respectively).48-56 The fact that the majority of the boron remains in the condensed phase is in agreement with the fact that boric oxide is a good afterglow suppressant. The mode of action can be summarized in the following equation (not balanced). 

Shen, K.K. and Griffin T.S. 1990. Zinc borate as a flame retardant, smoke suppressant, and afterglow suppressant in polymers. In Fire and Polymers (ACS Symposium Series, vol. 425), Nelson G.L. (ed.). American Chemical Society, Washington, DC, p. 157. 

Borax Einope and US Borax sell hydrated zinc borate flame retardants under the Firebrake name. Firebrake ZB is an example it has the formula 2ZnO.3B2O3.5H2O and the average particle size is seven microns. Firebrake 500 withstands high temperatures because it consists of anhydrous zinc borate, with no water to lose. It can be used in polyetherketones, polysulfones, fluoropolymers, polyesters and polyamides. It has a very beneficial effect on the heat release rate, suppresses smoke and afterglow, as well as promoting char. It is recommended for aircraft applications. 

The finding that boron remains in the condensed phase is consistent with reports that zinc borate is a good afterglow suppressant [133]. At combustion temperatures, studies of the zinc oxide-boric acid phase diagram [ 134] have established that zinc borate separates into a nearly pure, molten, boric oxide phase and a 1 1 zinc borate (Zn0 <.B203). Both boron and boric oxide are known to be strong inhibitors of the oxidation of carbonaceous materials [135]. 

The ZB 400 Series of Charmax Zinc Borates retain their water of hydration at high enough temperatures to process polyamides, polypropylene, and thermoplastic elastomers where they are also used as afterglow suppressants and anti-arcing agents. 

In particular in halogen-free systems, there are major advantages with respect to smoke suppression, afterglow suppression, corrosion inhibition, by combining zinc borates with other flame retardants in certain polymers, such as ethylene vinyl acetate, polyfvinyl chloride), poly(amide) (PA). 

The Charmax ZB Series of Zinc Borates are ultraflne, white flame retardant/ssioke suppressant powders that can also be used for reduced afterglow and arc/track. 

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