Zinc hydroxystannate as an alternative synergist to antimony trioxide in polyester resins containing halogenated flame retardants

Limiting oxygen index and Cone Calorimeter tests have been used to evaluate a number of inorganic synergists in polyester resin formulations containing various halogenated flame retardants. Zinc hydroxystannate (ZHS) is found to be a good alternative synergist to antimony trioxide, particularly with regard to reducing heat release rates and smoke generation. Hence, ZHS is recommended for use in conjunction with chlorinated paraffins, tetrachlorophthalic anhydride, chlorendic anhydride, dibromoneopentyl glycol or hexabromocyclododecane, but not with Dechlorane Plus, tetrabromophthalic anhydride or decabromodiphenyl oxide. A degree of synergism between ZHS and iron(III) oxide exists in certain systems and, provided that coloration does not preclude the use of the iron compound, such mixtures can lead to lower-cost formulations. Analysis of char residues from burnt polyester resin samples suggests that, whereas antimony trioxide exerts its flame-retardant action almost exclusively in the vapour phase, ZHS exhibits both condensed-and vapour-phase activity. (C) 1997 Elsevier Science Limited.