Zinc stannate interactions with flame retardants in polyamides; Part 2: Potential synergies with non-halogen-containing flame retardants in polyamide 6 (PA6)

Zinc stannate is a well known synergist and smoke suppressant with brominated flame retardants in a number of polymers but its possible synergistic function with phosphorus-containing species is less well documented. This paper reports the effect of adding zinc stannate together with aluminium diethyl phosphinate, an aryl phosphate (resorcinol bis (diphenyl phosphate)), a cyclic organophosphonate, melamine polyphosphate and melamine cyanurate singly or in combinations in polyamide 6 (PA6).Compounded formulations restricted by the need to maintain a maximum level of 20 wt% or less and an assumed constant molar ratio, Sn/P = 2/3, were characterized by DTA/DTG, limiting oxygen index, UL94, cone calorimetry and tensile testing procedures.Of the formulations studied, that comprising 10 wt% melamine polyphosphate, 5 wt% aryl phosphate and 7.5 wt% zinc stannate produced one of the highest LOI values of 26.5 vol% and a UL94 V2 rating. Clear evidence is provided that zinc stannate functions as a synergist only when these two phosphorus-containing species are present and not when individually present. The addition of zinc stannate to all formulations improved tensile property retention.The further addition of either zinc borate or a nanoclay appeared to negate any previously observed zinc stannate-phosphorus synergy in PA6.