Mechanism of intumescence of a polyethylene/calcium carbonate/stearic acid system

In this work, we have investigated the intumescent behaviour of linear low-density polyethylene (LLDPE) containing calcium carbonate (chalk) treated by stearic acid. This system swells during burning and creates a protective layer when exposed to an external heat flux of 50 kW/m2 in a mass loss calorimeter. This system has been fully characterized by FTIR, XRD, TGA and SEM. The carbonation/decarbonation temperatures, the swelling phenomenon and the effect of the thermal stress on the swelling have been examined. The residue is composed of a smooth surface made of chalk and CaO and a bulk of only chalk. Stearic acid allows a good dispersion of chalk particles into the LLDPE matrix, and contributes to form a cohesive network during burning when the thermal stress is high enough. A governing parameter of the intumescent effect is the particle size, which permits the formation of an insulating and cohesive mineral network during burning.