Abstract-Oxygen index results for a series of unsaturated polyesters, containing molybdenum oxide and various halogenated compounds, have provided definite evidence for some form of flame retardant synergistic effect between molybdenum and halogen. With the halogenated compounds used, the magnitude of the effect was greater in the presence of bromine but was dependent on the type of compound. When dibromoneopentyl glycol was used as the bromine source, the synergistic effect exhibited by molybdenum oxide was comparable to that shown by antimony oxide. Since molybdenum oxide also acts as a smoke suppressant, it could offer a useful alternative to antimony oxide particularly in the light of probable changes in standards and regulatory control regarding smoke emission.
IntrQductionDURING THE last three decades a vast number of flame retardant additives have been suggested and patented for use in various polymer formulations.1 Since polymers burn and degrade by different mechanisms and there are many desirable properties required of a flame retardant,z it is not surprising that a universal flame retardant does not exist. The most commonly used commercial compounds are based on the elementschlorine, bromine, antimony, phosphorus and boron. Using various combinations of these available flame retardants it is possible to exercise reasonable control over the rate of burning and flame spread in polymers. These systems do little, however, to reduce the amount of smoke generated by a polymer if it burns and there is evidence to suggest that flame retardant polymer formulations usually generate a denser smoke than untreated ones. This is particularly disturbing when an analysis of the statistics of fire casualties in the United Kingdom3 and in North America4 shows that the effects of smoke and toxic gases are increasing and now account for almost 50% of all deaths-smoke being one of the main causes of death.The recognition of the smoke and toxicity hazards of burning plastics has resulted in a need for the development of flame retardant formulations which incorporate smoke suppressant properties. Recent reports5-7 have illustrated that certain molybdenum compounds are potential smoke suppressants and that they also behave as flame retardant synergists in the presence of halogencontaining compounds. The original study on molybdenum by Moore and Church597 involved a screening evaluation of the effect of selected molybdenum compounds, mainly molybdenum oxide and ammonium dimolybdate, on the burning characteristics of PVC and unsaturated polyester resins-two plastics which consume large quantities of flame retardants. Since the initial trials were geared to the use of the inorganic molybdenum compounds as replacements for antimony oxide, polymer formulations were prepared containing the molybdenum compounds and/or antimony oxide and evaluated for their flame retardancy and smoke formation using the Michigan Chemical Corporation's Oxygen Index-Smoke Densitometer Unit. In both the PVC and the polyester resin (Atlac 711-O5A, an I.C...
