The prevailing mechanisms for halogen and phosphorus flame retardancy are reviewed. Halogens act in the vapor phase and phosphorus can act in either the vapor or condensed phase depending on the specific phos phorus compound and the chemical composition of the polymer. Halogen- antimony synergy is discussed. Convincing evidence is presented for bromine- phosphorus synergy in specific polymers. The mode of decomposition of polycarbonate is shown and the effect of salts of organic acids in changing the mode of decomposition hence producing a more flame resistant polymer is shown. Intumescence in polyolefins is discussed. Inorganic metal hydrates used in large concentration cool by endothermically releasing a large concentration of water. The effect of boron compounds is discussed. Methods of smoke suppres sion are presented as is the role of zinc borate, molybdenum and tin compounds acting as Lewis acids in PVC.

The flame retardant mechanism described for phosphorus- containing flame retardants includes both a condensed and a vapor phase mechanism depending on the type of phosphorus compound and the polymer. Intumescence is also described. Chemical structures of the flame retardant are shown. Specific applications for red phosphorus, organophosphates, chlorophos phates and bromophosphates are described. The use of triarylphosphates in PVC, modified polyphenylene oxide, and polycarbonate/ABS is described. The chlorophosphates are used in polyurethanes and the bromophosphates in en gineering thermoplastics. Flammability and mechanical properties are given for specific polymers.

Phosphorus-containing flame retardants include red phosphorus, inorganic phosphates, organophosphorus compounds and chlorophosphorus compounds. These are reviewed showing chemical structure and major applica tions. U.S., Western Europe and Japanese producers are given along with their trade names. Intumescent phosphorus systems and compounds are discussed.

A brominated phosphate was evaluated as a flame retardant in a polycarbonate and various polycarbonate blends. This flame retardant was found to be significantly more effective than an all-bromine and an all- phosphorus flame retardant, and bromine-phosphorus synergy was demon strated. The synergy is more pronounced when both the bromine and phosphorus are in the same molecule. The brominated phosphate is melt blendable and acts as a processing aid increasing extrusion output, lowering injection molding temperature and reducing energy consumption. The polymers investigated were polycarbonate, polycarbonate/ABS blend and poly carbonate/PET blend, as well as modified polyphenylene oxide.

The literature contains many claims to phosphorus/bromine flame retardant synergy. Many of these reports appear to be based upon a nonlinear response-concentration relationship. This paper shows convincing data for synergy in a a 2/1 polycarbonate/polyethylene terephthalate blend. The literature also shows phosphorus efficiency as a flame retardant to be 3-8 times more effective than bromine, depending on the polymer and flame retardant. These data show phosphorus to be about ten times more effective than bromine in a 2/1 polycarbonate/PET blend. Brominated phosphates, where both bromine and phosphorus are in the same molecule, were also studied. In one case synergy is further enhanced when both phosphorus and bromine are in the same molecule. On a weight basis, phosphorus and bromine in the same molecule are perhaps the most efficient flame retardant combination. KEY WORDS: flame retardants, phosphorus flame retardants, bromine flame retardants, synergy, phosphorus/bromine synergy, brominated phosphates, polycarbonate/polyethylene terephthalate blend, flame retarded engineering thermoplastics.