An investigation of the flame‐retardant and smoke‐suppressant properties of tin (IV) oxide in unsaturated polyester thermosets

Studies have been carried out of the effects of (1) anhydrous tin (IV) oxide and (2)β‐stannic acid {hydrous tin (IV) oxide} on the flammability and smoke production of unsaturated polyesters into which halogen may be introduced as a reactive monomer during the resin synthesis. The results obtained provide evidence for a marked falme‐reatedant synergism between tin and halogen, accompanied by a significant reduction in smoke from the burning polymer. The hydrous tin compound was found to be more effective than the anhydrous SnO2 both as a flame retardant and a smoke suppressant. At a 2% incorporation level β‐stannic acid gave polymers with LOIs of up to ca 30 and reductions in smoke density of 50% or more compared with the standard non‐halogenated resin. The mode of action of the tin compounds appears to involve both the condensed and vapour phases. In view of the generally accepted low toxicity of inorganic tin chemicals their possible use as fire‐retardant additives for polymer systems should merit serious consideration.