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].

Recently, on 9^th 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  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.

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, 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,  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 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 

The rising time occurs when foam mix starts to rise until it gets to a full block height. At this stage the isocyanate reacts with water to generate carbon dioxide which causes the rise. The formation of the carbon dioxide through the

intermediate carbamic acids gives.

RH = C = O + H – O – H           RNH COOH         RNH₂ + CO₂  

The curing time is the reaction process that leads to completion of the polymerization reaction that is usually greater than 15 hours. Polyurethane can either be flexible or rigid depending on the nature of the polymer and cross linking produced. In the production of flexible polyurethane foam, the polymerization reaction takes place between a difunctional polyol and tolune diisocyanate. Flexible polyurethane foams can be classified base on the density: low density, 16-24 kg/m², medium density, 32-48kg/m³ and  high density; 48kg/m³ and above [7].

The two basic types of flexible polyurethane foams are polyester and polyether flexible polyurethane foams.

Polyesters are used mainly for clothing, interlining and packaging while polyether are used to produced mattresses, cushions and general upholstery [8]. Flexible polyurethane foams can be produced in many grades of flammability, elongation and load bearing capacities.

The level of flammability of the polyurethane foams is of great concern both to the foam industries as well as whole masses. In order to reduce the flammability of these polyurethane foams, and hereby reducing the destructive tendencies of fire outbreaks some suitable flame retardants are incorporated into the foam. This study aims at producing a flame retarded polyether flexible polyurethane foam of melamine and tri ammonium orthophosphate in various formulations.

1.2 Significance of the Research.

Flexible polyurethane foams are used in several applications  in homes, (mattresses, cushions), industries (automobile, packaging etc); hence decrease in their flammability will save lots of life and properties in event of fire outbreak in these areas.

•              Establishing the effects of using different concentration of the applied fire retardants to the flexible polyurethane foams will be valuable to commercial foam manufacturers and researchers in the polymer industry.

•              Statistical establishment of the better fire retardants out of the two on the fire characteristics of flexible poly urethane foams will be useful to commercial foam manufacturers.

•              Comparison of the fire characteristics of flame retarded polyurethane foams with the existing commercial foams will clear the doubt of whether commercial manufacturers actually incorporate fire retardants or not.

1.3 Scope of the Study

*              The study was based on only flexible polyether foams.

*              The flame retardants incorporated in various formulations are melamine, (C₃H₆N₆) and triammonium orthophosphate (NH₄)₃.(P0₄.3H₂0).

*              The fire characteristics that were tested include: flame propagation rate, ignition time, after glow time, % char formation, and flame duration.

1.4 The objectives of the Study;

*              The effects      of     melamine and triammonium

orthophosphate on the fire characteristics of the flexible polyurethane foams were investigated. 

*              The fire characteristics of flexible polyurethane that was flame retarded with melamine was compared with

                that      of      flame     retarded      with     triammonium

orthophosphate. 

*              The reduction of the flammability of the flexible polyurethane foams was verified.

*              The extent of the effects of the two flame retardants on the ignition behaviour of flexible polyurethane foams was established.