In view of the current demand for novel, non-toxic, flame-and smoke-suppressant systems for synthetic polymers, certain inorganic tin compounds have been evaluated as fire retardants in a series of commercial brominated polyester resin formulations. The results obtained clearly show that zinc hydroxystannate (ZnSn(OH),) and zinc stannate (ZnSnO,) impart beneficial properties to the polyesters in terms of flame retardancy and smoke/carbon monoxide suppression, and the improvements in performance are, in general, superior to those exhibited by tin (IV) oxide or antimony (m) oxide. The surface area and degree of dispersion of the fire-retardant additive has been shown to have a marked effect on its efficiency and, in this connection, colloidal tin (IV) oxide is found to exhibit significantly improved flame-retardant properties compared to powdered SnO,. Simultaneous thermal analyses (TG/DTG/DTA) and related mechanistic experiments have shown that tin additives markedly increase the amount of char formed during combustion,,whereas Sbp,, a vapour-phase flame retardant, has little effect on char formation.The zinc stannates also appear to exhibit a significant vapour-phase activity, and this may account for their flame-retardant superiority to SnO, itself.
INTRODUCTIONThe fire-performance characteristics of unsaturated polyester resins are of the utmost importance in many application areas, particularly in the construction, transportation and electronics industries. ' Although several flame-retardant systems have been developed for use in organic polymers, many of these are known to increase the amount of smoke and toxic gases generated by the plastic if it burns., Since these combustion products are now known to be the major cause of death in fire^,^ recent advances in fire testing have placed great emphasis on developing products that have low flame spread properties and are low smoke producing.In a previous programme of studies, tin (IV) oxide, both in its anhydrous and hydrous forms, was found to be an effective flame-and smoke-retardant in a number of laboratory-prepared polyester formulation^.^ This paper reports an extension of the work, in which studies are carried out into the flame-, smoke-and carbon monoxide-suppressant properties of inorganic tin compounds in a series of commercial brominated polyester resins. The identities of the products were confirmed by infrared spectroscopy and X-ray powder-diffraction patterns. Physical data on the inorganic tin additives studied are given in Table 1.The commercial additive used in this work was antimony (111) oxide (May & Baker Ltd, Dagenham). The brominated polyester resin (Stypol R1264/6), was supplied by Freeman Chemicals Ltd, Ellesmere Port, and contains 28% bromine as the reactive intermediate, dibromoneopentylglycol (DBNPG). The halogen-free general-purpose polyester resin used was Crystic 471 PA LV (Scott-Bader Co. Ltd, Wellingborough).
Incorporation of additivesThe inorganic additives were mixed into the resin using a Silverson high-shear mixer in order t...
