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Mode of Action

The most important fire retardant effects of mineral fillers can be summarized as follows:

  • 1. Endothermic decomposition, absorbing heat and therefore keeping the surrounding polymer cooler.
  • 2. Production of inert diluent gases. Flaming reactions require a critical concentration of free radicals to be self-sustaining. If this concentration falls sufficiently, for example, by the release of water or carbon dioxide, flame extinction will occur.
  • 3. Accumulation of an inert layer on the surface of the decomposing polymer, shielding it from incoming radiation, and acting as a barrier to oxygen reaching the fuel, flammable pyrolysis products reaching the gas phase, and radiant heat reaching the polymer.
  • 4. Incorporation of any noncombustible filler reduces the flammability of a polymer, by reducing the total amount of fuel, the rate of diffusion of oxygen into, and fuel from, the polymer bulk while increasing the heat capacity, thermal conductivity, reflectivity, and emissivity.

These effects are discussed in detail in section “Fire Retardant Effects of Mineral Fillers.” First, however, a summary of the two fundamental thermal analysis techniques, thermogravimetry (TGA) and differential scanning calorimetry (DSC), is given to contextualize the decomposition data used to illustrate the fire retardant effects of these materials.

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