These days polyurethane foam provides a large part of our daily needs due to its many applications along with unique features including heat insulation, sound insulation, moisture insulation and more.But polyurethanes are organic chemicals, like other organic materials, if they exposed to a sufficient source of heat, are flammable and may cause irreparable catastrophes and damage. Moreover, the physical structure of Polyurethane has effect on their flammability, for example soft polyurethane foams that contain open cells, in which they can penetrate high volumes of oxygen, which is a major reason for the ignition. Therefore, it is necessary to take actions to reduce the flame retardant potential of these materials and ultimately increase their fire resistance, using materials called flame retardants.
The Solution To the Problem
One of the most effective ways of flame retardancy polyurethanes is to use additives containing halogenated compounds. Over the past few decades, the widespread influx of flame retardants into the manufacturing process of many polyurethane products has increased, so that fire cannot easily destroy them. There are various types of fire retardants, which are usually classified by their chemical structure or properties. It should also be borne in mind that these types of materials reduce the rate of flame propagation. The classification of flame retardants, which can prevent flammability and inhibition in different polymers under different conditions, is as follows:
- Halogenated compounds: They enter the gas phase and actually interfere with the oxygen-hydrogen reaction that they have previously created. It either hydrogenates the existing hydrogen, or disables the free radicals produced by polymer decomposition by creating a halogen radical.
- Metal oxides: These inhibitors act by modifying the mechanism of polymer decomposition in the solid or gaseous phase. Some of the materials in this group cause the cooling temperature to decrease.
By choosing flame retardants, several factors should be considered such as non-surface migration, compatibility with other raw materials, non-alteration of physical and mechanical properties, and most importantly non-emission of smoke or toxic gases. The mechanism of flame-retardant materials is comprised of one of the following steps:
- Flame Reaction and Prevent Spread Reaction by Disabling Radicals
- Suppress flame by covering gases and keeping polymer and oxygen separate
- Cool the flame by extracting energy and lowering its temperature
- Coal forming and forming a gap between solid polymer and decomposed product
- The blowing and swelling of the polymer and the thermal separation between the flame and the product resulting from the thermal decomposition
B2 test
One of the most commonly used standards in this field is DIN 4102, it used to investigation the flammability and the combustion of products containing flame retardant additives. This standard defines fire behavior classes for building materials and specifies the requirements and testing methods for each class. DIN 4102 is divided into two classes, A and B.
- Non-combustible materials
- Combustible materials are classified into three different groups: B1 (not easily flammable), B2 (flammable with self-extinguishing properties) and B3 (easily flammable).
This test requires equipment and requirements. The specimen is hung on a holder in a chamber according to this standard and the flame is applied for 15 seconds. The arrival time of the flame to the specified point is measured at a distance of 12 cm from the flame tip. If the flame encompasses the entire sample, it means that the foam is generally burnt and has no fire resistance, hence it falls into category B3. If, after removing the flame, it is switched off after a short burn and does not pass the specified point, the sample shall be placed in group B2. Type B1 is not easily flammable, extinguishes immediately after flame removal.
