The effectiveness of alum and potassium sesquicarbonate was studied by incorporating various concentrations of the flame retardants into the polyurethane foam sample. The flammability tests were carried out and the results showed that as the concentration of the flame retardants increased, the flame propagation rate, after glow time, burn length and flame duration decreased for both flame retardants, while ignition time, add-on and char formation increased for both flame retardants. Thermogravimetric analysis shows that both alum and potassium sesquicarbonate functions as flame retardants on the foam samples at low percentage concentration but the polyurethane foam filled with potassium sesquicarbonate required a higher activation energy than alum for the pyrolysis / combustion of the samples. Also the onset of degradation time was more delayed in potassium sesquicarbonate than alum.

In every day to day activity, foam materials are all around our homes, vehicles, schools and industries. It is the cushioning material of choice in almost all furniture and bedding. It is used as carpet cushions. It is the material used for pillows, roof liners, sound proofing, car and truck seats. Foam has become such a widely used material because it provides a unique combination of form and function [1].

Types of foam such as neoprene, polystyrene, polyethylene, polyurethane, polyether and polyester based polyurethane are synthetic plastics that have very desirable properties; easily malleable and shapeable. They are also capable of “giving” and returning to its original shape [2].

Polyurethane foams which have been in use for almost 40 years, offer a wide variety of product suitable for various applications. It appears to be a simple product but actually very complex. The market place for polyurethane has witnessed innovations and improvement which have led to great usage. Polyurethane is a good example of traditional organic polymer system that has useful structural and mechanical properties in foam but it is limited by its low thermo-oxidative stability [3].

New technologies , new processes and new applications introduce new fire hazards (e.g. new ignition sources such as welding sparks and short circuits) [4]. Modern fire fighting techniques and equipments have reduced the destruction due to fires. However, a high fuel load in either a residential or a commercial building can offset even the best of building construction [5]. Wood, paper, textiles and synthetic textiles all burn under the right conditions, many burn rigorously and ignite readily. The ability to control or reduce flammability of materials have engaged the mind of scientists. Fire hazards may be reduced by either retarding the fire or initiating a chemical reaction that stops the fire. It has been observed that some of the fire retardant chemicals have adverse effects on the properties of materials on which they are imparted [6]. The choice of suitable polymeric flame retardants is restricted to species that allow the retention of advantageous properties of the polyurethane.

1.1       Flame retardants
Flame retardants are materials that resist or inhibit the spread of fire. They are chemicals added to polymeric materials, both natural and synthetic to enhance flame retardant properties [7]. A fire retardant is a material that is used as a coating on or incorporated into a combustible product to raise the ignition or to reduce the rate of burning of product [8].

Chemicals used as flame retardants can be inorganic, organic, mineral, halogen or phosphorus-containing compounds. In general, fire retardants reduce the flammability of materials by either blocking the fire physically or by initiating a chemical reaction that stops the fire. Flame retardant systems used in synthetic or organic polymers act in five basic ways [7].

1.                  Gas dilution:- This involves using additives that produce large volumes of non-combustible gases on decomposition. These gases dilute the oxygen supply to the flame or dilute the fuel concentration below the flammability limit. Examples are metal salts, metal hydroxides and some nitrogen compounds.

2.                  Thermal quenching:- This is the result of endothermic decomposition of the flame retardant. Metal hydroxides and metal salts act to decrease the surface temperature and rate of burning.

3.                  Protective coating:- Some flame retardants form a protective liquid or char barrier which limits the amount of polymer available to the flame front and also act as an insulating layer to reduce the heat transfer from the flame to the polymer. This includes phosphorus compounds.

4.                  Physical dilution:- Inert fillers (glass fibres) and minerals act as thermal sinks to increase the heat capacity of the polymer or reduce its fuel content.

5.                  Chemical interaction:- Some flame retardants such as halogens and phosphorus compounds dissociate into radicals species that compete with chain propagating steps in the combustion process.

Flame retardants have faced renewed attention in recent years, aside from various conventional alternatives such as antimony or phosphorus based retardants which have toxicological problems of their own, nanoadditive flame retardants such as carbon nano tubes, nanographites, layered double hydroxides (LDH) have been shown to enhance a number of polymer properties, thermal stability, strength, oxidation resistance, processing, rheology and flammability in polyurethane foams [9].

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