Mechanism of condensed phase action in flame retardants. Synergistic systems based on halogen-metal compounds

Fire retardance mechanism in polypropylene/chloroparaffin/metal chloride sy stems (PP/CP/MC) using different chloride or chloride suppliers has been in vestigated and a synergistic effect has been recognised in some cases, whic h mainly involves a condensed phase effect. By studying PP/MC and CP/metal (0) mixtures separately it has been found that some MC are reduced by PP to M (0) (Cu+, Cu++, Sn4+, Sb3+, Bi3+) and some M (0) are oxidised by CP (Sn, Sb, Bi) depending on their standard reduction potential. The reaction betw een PP and MC, which consumes PP radicals reducing the rate of thermal oxid ation of PP, is responsible for the condensed phase effect of fire retardan ce. When both reduction of MC by PP and oxidation of M by CP is allowable ( Sn, Sb, Bi) a catalytic mechanism is established which leads to the synergi stic effect of fire retardance by regenerating the MC reduced by PP. Synerg istic effect with Cu compounds is explainable by involvement of Cu+/Cu++ re dox couple; Cd and Pb compounds does not show any synergistic effect. (C) 2 000 Elsevier Science Ltd. All rights reserved.