Intumescent flame retardants for polymers. II. The polypropylene‐ammonium polyphosphate‐polyurea system

Abstract

Abstract The mechanism of action of ammonium polyphosphate (APP) and polyurea (PU) as flame retardant (FR) agents for polypropylene (PP) was examined. The APP–PU system behaves as an intumescent flame‐retardant (IFR) formulation. Comparison of the oxygen index (OI) measured on molded pellets and rods, values of the polymer temperature measured just below the burning surface, and visual considerations describe the IFR action of this system. A strong synergism between APP and two of the four polyureas investigated here was ascertained with a maximum 3:1 ratio. Thermogravimetric (TG), OI, nitrous oxide index (NOI), and char‐residue measurements were made. On the basis of our data, it can be concluded that polyurea acts as a catalyst for the charring reactions of the APP on PP.