CHAPTER ONE

INTRODUCTION

1.1     Background

Fire is a world wild problem which claims lives and causes significant loss of properties. Most of the immediate surroundings of man consist of polymeric materials which are combustible materials. These include clothes, furniture, construction materials, and interior decorations. Generally, the interiors of homes, offices, vehicles, and packages are decorated with foamed plastics. The constitution of foamable polymeric materials made them liable to easy ignition and vigorous burning under right conditions. Humans have always been plagued by unwanted fire, which usually gulfed life and properties worth of millions of naira.

In addition to immediate fire risk posed by the polymeric materials while burning, their combustion products often cause serious threat to human health and environment. In United States between 1996 and 2005 it was reported that an average of 3,932 human loss and another 20,919 injuries were as a result of fire accidents [1].

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Recently, on 9th Oct 2009, along Enugu-Onitsha express road, over ten vehicles loaded full with humans and property worth millions of naira were engulfed by fire. Therefore, the need to seek efficient and affordable ways of reducing the flammability of polymeric materials in our surroundings is of primary importance.

A flame is a rapid free radical, chain reaction of volatile materials with oxygen in the air. It is actually the resultant flame or fire that consumes life and properties. The term fire retardant (flame retardant) describes materials that inhibit or resist flammability of polymers. In the same vein a fire retardant chemical is used to denote a compound or mixture of compounds that when added to, or incorporated chemically into polymers, serve to slow down or hinder the ignition or growth of fire [2]. In other words, a flame retardant chemical is therefore a compound or mixture of compounds which when added to or chemically incorporated into a polymeric material, substantially suppresses the ease of ignition and/or flame propagation [3].

The above definitions of flame retardant denote that it

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generally either lower ignition susceptibility or lower the flame propagation once the ignition has occurred. The products on which flame retardants can be applied include apparels, carpets, and rugs, construction materials (thermal) insulation foams, wall coverings and composites to meet governmental regulations for buildings, aircraft, auto mobiles. Flame retardants can be incorporated into a material either as a reactive component or as an additive component. As a reactive, such flame retardants are incorporated into the polymer structure of the plastics, example, when polyurethane and polyamides are retarded with red phosphorus.

Flame retardants are usually classified into three types: non durable, semi durable and durable finishes, based on durability, or fastness to (laundry) light, heat chemicals etc. [3].

i.            Non- durable finishes. These are used for packaging materials, paper and furnishings. They include formulations containing, borax and other borates. Others are aliphatic amine phosphate (e.g. triethanolamine phosphate), urea sulphamates,

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ammonium and diammonium phosphate, ammonium bromide and ammonium polyphosphate.

ii.          Semi durable finishes. These include flame retardants for mattresses, drapes, upholstery and carpets which can withstand 1-20 washings in water, for example, precipitate of a mixture of oxides of tungsten and tin in the soluble salts.

iii.        Durable finishes. These retardants are very durable and can import excellent antimony oxide with durable functions to cotton fabrics, for example chlorinated paraffin.

Most flame retardants contain elements from group III A, (boron and aluminum) group VA (nitrogen, phosphorus, arsenic and antimony) and group VII A (fluorine, chlorine and bromine) [4].

Group III: A flame retardant which contain boron or aluminum work by forming char which acts as a protective layer that prevents oxygen from reaching the inner layers of the material and thus sustaining the fire. Chemicals commonly used for this purpose include borax, boric acid,

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and hydrated aluminum oxide.

The group VA flame retardants work by forming a surface layer of protective char. These include phosphoric acid, diammonium orthophosphate and others, which are usually applied in cellulose, polyester, and polyurethane products. Arsenic is usually not used as flame retardant owing to its toxicity, antimony in itself is ineffective as a flame retardant, and it is used only in combination with halogens, especially bromine and chlorine.

The group VII: A flame retardants which are the halogens (Bromine, chlorine and fluorine). Bromine works as a flame retardant in gaseous phase. When Bromine containing compounds are incorporated into flammable materials, the bromine dissociates from the material and form a heavy gas, when the materials is exposed to flame. The dissociation disperses heat and the bromine gas forms an insulating layer around the material. The layer prevents flames from spreading by inhibiting access to oxygen and by slowing the transfer of heat. The use of these groups of fire retardants is somehow restricted because of their environmental

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implications. The flame retardants selected for the present study are from group VA, which is incorporated in flexible polyurethane form as a reactive not as an additive. Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters and phenolics [5]. A urethane linkage is produced by reacting an isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH. Polyurethanes are produced by the poly-addition reaction of a poly-isocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives [6].

During the production, excess isocyanate groups in the polymer with water or carboxylic acid produce carbon dioxide that blows the foam. Foaming reactions occur in three stages; the blow reaction lasts for about 12 seconds and occurs as soon as isocyanate reacts with polyol to give polyurethane and the polyurethane reacts further with isocyanate to produce an allophanate in a reversible reaction.

R1NHCOOR2 + R3N = CO  R1N (CONHR3) COOR2