Synergistic effect of zeolite in an intumescence process. Study of the interactions between the polymer and the additives

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Abstract
The chemical effect of the zeolite 4A added to the intumescent ammonium polyphosphate (APP)–pentaerythritol (PER) system in a fire retardant (FR) ethylene–butyl acrylate–maleic anhydride terpolymer (LRAM3.5)-based formulation has been studied. Thermogravimetric (TG) analysis defines the different steps of the degradation of the formulation and shows that the presence of the zeolite leads to an increase in the stability of the material at high temperature (T > 550 °C). Spectroscopic characterisations, mainly 31P, 13C, 1H and 27Al NMR of the solid state, demonstrate that there are interactions between the polymer and the additives. In the case of the LRAM3.5–APP–PER formulation, the protection arises principally from the additives which make a thermal barrier between the flame and the material. When zeolite is present it plays an essential role, because it allows the formation of structures stabilising the polymer which can then participate in the formation of the intumescent protective shield and hence in its own protection. Moreover, we prove that the FR properties of the protective material obtained from the formulations depend on the ‘quality’ of the intumescent coating obtained from the additives. In particular, the presence of the zeolite decreases the size of the amorphous domains of the carbon.