Pyrolysis studies of flame retarded plastic systems

Abstract

Two pyrolysis experiments have been utilised to investigate reactions pertinent to flame retardant behaviour. Firstly, a mass spectrometric evolved gas analysis technique has been used to study the influence of the flame retardant decabromodiphenyl oxide (DBDPO) and the synergists antimony oxide and zinc borate on the activation energy for monomer (i.e. fuel) evolution from polystyrene composites. When the polystyrene was compounded with all three additives, a negative value of −82.5 ± 5.0 kJ mol −1 was obtained for the activation energy. This is explained in terms of a condensed phase reaction between the DBDPO and polymer radicals which reduces monomer evolution. The rate of the former reaction increases more rapidly than the latter with increasing temperature. As a consequence the rate of monomer evolution is decreased as the temperature is raised, hence the observed negative activation energy. Secondly, the extremely fast scan capability of the time-of-flight mass spectrometer has been utilised to monitor HCl and benzene evolution from various poly(vinyl chloride) (PVC) composites subjected to a very large and rapid temperature rise due to pulsed laser heating. The benzene evolution behaviour observed is correlated with smoke density data obtained from the same materials. It is found that a decrease in the smoke density value can be associated with an increase in benzene evolution. This may well indicate that additives which result in benzene rather than higher aromatics being evolved may well be used to produce PVC composites with lower smoke production in a fire.