Mechanism of fire retardancy of polyurethanes using ammonium polyphosphate

Abstract

In this work, we studied the mechanism of the fire retardancy of ammonium polyphosphate (APP) in polyurethane (PU). Indeed, according to the limiting oxygen index test, the efficiency of APP in PU coating was proven. On the one hand, thermogravimetric analyses showed that the addition of APP to PU accelerates the decomposition of the matrix but leads to an increase in the amount of high‐temperature residue, under an oxidative or inert atmosphere. This stabilized residue acts as a protective thermal barrier during the intumescence–fire retardancy process. On the other hand, spectroscopic analysis of the charring materials using infrared spectroscopy, MAS NMR of the solid state, and ESR enables better understanding of the carbonization process and, consequently, of the intumescence phenomenon. It has been shown that the char resulting from PU consists of an aromatic carbonaceous structure which condenses and oxidizes at high temperature. In the presence of APP, a reaction between the additive and the polymer occurs, which leads to the formation of a phosphocarbonaceous polyaromatic structure. Moreover, this char is strongly paramagnetic. The presence of large radical species, such as a polyaromatic macromolecule trapping free radicals, was demonstrated. Both of these characteristics help to explain the fire‐retardant performance of PU/APP. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3262–3274, 2001

Flame-Retardancy Properties of Intumescent Ammonium Poly(Phosphate) and Mineral Filler Magnesium Hydroxide in Combination with Graphene

“…The second decomposition step of PP led to the total thermal oxidation of the charred residue by releasing CO and CO2. The decomposition of APP proceeded in two well-known steps [45,46]. Between 290 and 450 °C, condensation and cross-linking of the polyphosphate chains to poly (phosphoric acid) released NH3 and water.…”

Investigation of the thermal degradation of polyurea: The effect of ammonium polyphosphate and expandable graphite

“…APP is an effective intumescent fire retardant for several kinds of polymerbased materials and, in particular, for polyurethanes [14], [15], [16] and [17]. It is a high molecular weight chain phosphate, whose efficiency is generally attributed to an increase of char formation through a condensed phase reaction.…”

New intumescent flame‐retardant agent: Application to polyurethane coatings

“…Moreover, PUs are also extensively used as resins for lacquers, varnishes, and coatings; composites in synthetic leather, adhesives, and spandex fibers; and they can be cast, injection molded, or extruded as elastomers. [1][2][3][4][5] PU-based coatings have recently assumed an important place in the coatings industry. In some applications, they dominate the market because of their high level of quality.…”