Abstract: Progress in the synergistic agents of ammonium polyphosphate (APP) intumescent flame retardant (IFR) system was reviewed. The application of IFR and its synergistic agents in polymer materials was introduced. Four categories of synergistic agents for IFR containing ammonium polyphosphate, such as zeolite, metal oxide and metal salt, metal hydroxide, and expanded graphite were introduced. The flame retardancy and the flame retardant mechanism were also discussed. It was shown that the efficiency of the IFR could be remarkably improved by the addition of synergistic agents, and the harm to the matrix and the loading level were also decreased. The study on the synergistic agents also promoted the study on surface modification and micro-encapsulation of APP.

Key words: ammonium polyphosphate (APP), intumescent flame retardants (IFR), synergistic agent, flame retardant mechanism