Synergistic catalysis effects of lanthanum oxide in polypropylene/magnesium hydroxide flame retarded system

Lanthanum oxide (La2O3) was incorporated as a catalytic synergist to enhance the flame retardancy of the environmental friendly halogen free inorganic compound magnesium hydroxide (MH), the main flame retardant, filled in the flammable polymer polypropylene (PP) matrix. It was found that the addition of an appropriate loading of La2O3 could remarkably improve the flame retardancy of MH filled PP FR composite. The significant enhancement in the flame retardancy was attributed to the greatly improved quality of the condensed phase charred layers deposited on the surface of the formed magnesium oxide (MgO) particles through participation of PP macromolecular chains themselves in the char formation reaction under the catalytic action of La2O3. It was believed that the char formation reaction involved with the PP macromolecular chains is composed of two processes related to the catalytic role of La2O3, i.e. catalytic oxidation hydrogenation and catalytic partial oxidation.