**2. Polyurethane foam morphology**

102 Polyurethane

radical blocks.

area.

groups.

polymer.

2. Preventing of the oxygen diffusion into the polymer

cause to reduce the flame temperature.

1. Reaction with the flame and preventing of the spreading of the fire by the created free

4. Char creation and creating a free place between the solid polymer and the disposed

5. Polymer expansion and making a free place between the fire and the decomposed

There are lots of materials which are known as the fire retardants according to the following

 Halogenated flame retardants which are acting in the gas phase with disturbing the hydrogen-oxygen reaction. They react with hydrogen and create the halogen free

Metal oxides which act in solid or gas phase and some of the members of this group

Phosphorous containing compounds which create char on the extinguishing area of the

 Halogen free FR which the two main candidates are EG and Melamine. The heat stability of the polyurethanes especially the rigid foams at high temperatures depend on the isocyanurate to allophanates and biurets cross-linked bond ratio. Carbodiimide is produced by the condensation reaction of isocyanate with lose of CO2 (Fig.1). This reaction can be catalyzed by the cyclic phosphine-oxide. Generated carbodiimide is used as an unti-hydrolyze agent in the polyurethanes. The heat stability of the diverse

3. Lowering of the flame temperature with **removing energy from the system** 

radicals then they block free radicals of decomposed polymer.

polymer and prevent the oxygen feeding to the flame.

products of polyurethanes is classified in Table (1).

**Figure 1.** Condensation reaction of isocyanate to make Carbodiimide

Polyurethane morphology plays a vital rule on the fire properties of the polyurethane foam. The porous structure of the foam helps to diffuse the oxygen easily in to the foam and accelerate the ignition process. Fig.2 shows the SEM Picture of the polyurethane flexible foam with no filler inside. As it is clear, the cell structure of the foam includes Cell window, Strut and Strut joint [1].

**Figure 2.** Fundamental concepts of polyurethane foam Cell Structure (SEM×200)
