SynopsisAddition of red phosphorus in concentrations of about 4% to poly(ethy1ene terephthalate) (PET) reduces the flammability of that polymer. The rates of flame propagation and the ignitability are reduced, while the oxygen index (0.1.) is increased. The surface temperature of burning PET amounts to Ts = 38OOC; addition of 4% red phosphorus raises this value to Ts = 45OOC.An increase of the environmental temperature TE enhances the flammability of PET and PET + phosphorus samples; the 0.1. decreases and the rate of flame propagation increases with temperature. The flame-retardant effectiveness of red phosphorus is reduced if the sample is burned in a NzO atmosphere. This indicates that part of the flame retardancy imparted by phosphorus involves gas-phase inhibition. The major flame-retardant action does, however, occur in the condensed phase, since the rate of pyrolysis of PET is affected by the presence of red phosphorus.

SynopsisFlame retardant formulations for polypropylene are described that comprise a heat-stable phosphonium bromide or phosphine oxide, containing cyanoethyl substituents, in combination with ammonium polyphosphate. A t additive levels of (20-30)%, flame-retarded polypropylene, with an Underwriters' Laboratories UL 94 V-0 rating is obtained with little effect on thermal and mechanical properties of the polymer. A characteristic property of this flame retardant mixture is low smoke generation during burning. Mechanism studies indicate that the organophosphorus component alone acts as an inhibitor in the gas phase, whereas the ammonium polyphosphate alone acts in the condensed phase. The synergistic effect observed by the combination of these two components is due to the formation of a phosphorus-rich char which forms an insulating layer.