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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.

SynopsisThe influence of elemental red phosphorus on the rate of thermal degradation of poly(ethy1ene terephthalate) has been studied in the temperature range of 400" to 500°C in inert and oxidizing atmospheres by means of isothermal thermogravimetric analysis. Addition of red phosphorus is found to reduce the rates of both the pyrolytic and the thermo-oxidative degradation and to increase the amount of residual char. A correlation of pyrolysis rates with oxygen index data has been attempted.