The thermal degradation kinetics and flame-retarding mechanism of a new intumescent halogen-free flame-retarding high impact polystyrene (HIPS) were studied by the conventional dynamic thermogravimetric analysis (TGA). The parameters of the thermal degradation kinetics were ratified by comparing the Kissinger mold with the Coat-Redern mold. Therein, according to the ordinary reaction limit of Ea/RTmax, the reaction nth-order was ascertained by the relationship between αmax and n at the maximum reaction rate. By means of TGA-FTIR and Py-GC/MS, the flame-retarding mechanism was analyzed. The experiment results indicated that the parameters of the thermal degradation kinetics were similar by the two molds, and it turned out to be that the activation energy of the flame-retarding HIPS was less than that of pure HIPS, in other words, the flame retardant has already been decomposed before HIPS decomposition, releasing a great deal of non-flaming gas (such as ammonia and its ramification, water vapour and so on), then retarding flaming in air. At the same time, adding the flame retardant resulted in promoting the reaction to chain-transfer, then decreasing non-monomer in flame and forming the char crosslink, which could stop flaming in air and isolate heat transfer in condensed phase.

Key words: high impact polystyrene, kinetic, thermal degradation, flame retardant, halogen-free