Tin Compounds as Flame Retardants and Smoke Suppressants

During the 1970s, aqueous solutions containing tin(IV) chloride and ammonium bifluoride found commercial application as flame-resistant treatments for woollen sheepskins and rugs, - where they had the advantage over competitive titanium and zirconium fluoride systems of not imparting any yellow 

---

At the present time, inorganic tin compounds find a relatively small use in natural polymers, particularly as flame-resist treatments for woollen rugs and sheepskins (8,9). Although certain other metal derivatives have received more attention, there has been much interest recently in the potential use of tin chemicals as flame retardants and smoke suppressants for synthetic polymers (10). 

However, as far as plastics are concerned, commercial interest in the use of tin-based flame retardants has only developed over the past 10 years or so. Although it is estimated that over 600 000 tonnes of chemical additives are used worldwide annually as flame retardants for s)mthetic polymers, recent concerns about the toxic nature of certain additives have led to an intensified search for safer flame retardants. Hence, the generally low toxicity of inorganic tin compounds has been a major factor in their growing acceptance throughout the 1990s as flame retardants and smoke suppressants for plastics, elastomers and other polymeric materials. 

Hence, it is apparent that certain inorganic tin compounds are very effective flame retardants and smoke suppressants for halogenated polymer formulations. Since these additives are generally non-toxic, their potential use as partial or total replacements for existing commercial flame retardants, such as antimony trioxide, is thought to merit serious consideration. 

Tin oxide, Sn02, has also been studied as a flame retardant and smoke suppressant in conjunction with chlorine or bromine compounds. Performance was found to be generally less effective than that of the zinc stannates, which also contain less tin, and are hence more cost effective. 

With regard to practical usage, one of the major application areas for ZHS and ZS has been in flexible PVC wire and cable insulation, where the tin additives have been selected because of their combined flame-retardant/smoke-suppressant properties. The grades of ZHS/ZS used must have very low electrolyte levels and must not contain any free zinc oxide, since the presence of the latter compound can result in a phenomenon known as zinc burning, in which the PVC undergoes dehydrochlorination during processing. 

---