Phosphorus-Bromine Flame Retardant Synergy in a Polycarbonate/Polyethylene Terephthalate Blend

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 retar dant. 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.