Investigation of effects of two flame retardants on the fire characterisitics of flexible polyether foam

Thesis Overview

<p> </p><p>Background<br>Fire is a world wild problem which claims lives and causes<br>significant loss of properties. Most of the immediate<br>surroundings of man consist of polymeric materials which<br>are combustible materials. These include clothes, furniture,<br>construction materials, and interior decorations. Generally,<br>the interiors of homes, offices, vehicles, and packages are<br>decorated with foamed plastics. The constitution of foamable<br>polymeric materials made them liable to easy ignition and<br>vigorous burning under right conditions. Humans have<br>always been plagued by unwanted fire, which usually gulfed<br>life and properties worth of millions of naira.<br>In addition to immediate fire risk posed by the polymeric<br>materials while burning, their combustion products often<br>cause serious threat to human health and environment. In<br>United States between 1996 and 2005 it was reported that<br>an average of 3,932 human loss and another 20,919 injuries<br>were as a result of fire accidents [1].<br>2</p><p>Recently, on 9th Oct 2009, along Enugu-Onitsha express<br>road, over ten vehicles loaded full with humans and property<br>worth millions of naira were engulfed by fire. Therefore, the<br>need to seek efficient and affordable ways of reducing the<br>flammability of polymeric materials in our surroundings is of<br>primary importance.<br>A flame is a rapid free radical, chain reaction of volatile<br>materials with oxygen in the air. It is actually the resultant<br>flame or fire that consumes life and properties. The term fire<br>retardant (flame retardant) describes materials that inhibit<br>or resist flammability of polymers. In the same vein a fire<br>retardant chemical is used to denote a compound or mixture<br>of compounds that when added to, or incorporated<br>chemically into polymers, serve to slow down or hinder the<br>ignition or growth of fire [2]. In other words, a flame<br>retardant chemical is therefore a compound or mixture of<br>compounds which when added to or chemically incorporated<br>into a polymeric material, substantially suppresses the ease<br>of ignition and/or flame propagation [3].<br>The above definitions of flame retardant denote that it<br>3</p><p>generally either lower ignition susceptibility or lower the<br>flame propagation once the ignition has occurred. The<br>products on which flame retardants can be applied include<br>apparels, carpets, and rugs, construction materials<br>(thermal) insulation foams, wall coverings and composites to<br>meet governmental regulations for buildings, aircraft, auto<br>mobiles. Flame retardants can be incorporated into a<br>material either as a reactive component or as an additive<br>component. As a reactive, such flame retardants are<br>incorporated into the polymer structure of the plastics,<br>example, when polyurethane and polyamides are retarded<br>with red phosphorus.</p><p>Flame retardants are usually classified into three types: non<br>durable, semi durable and durable finishes, based on<br>durability, or fastness to (laundry) light, heat chemicals etc.<br>[3].<br>i. Non- durable finishes. These are used for packaging<br>materials, paper and furnishings. They include<br>formulations containing, borax and other borates.<br>Others are aliphatic amine phosphate (e.g.<br>triethanolamine phosphate), urea sulphamates,<br>4</p><p>ammonium and diammonium phosphate, ammonium<br>bromide and ammonium polyphosphate.<br>ii. Semi durable finishes. These include flame retardants<br>for mattresses, drapes, upholstery and carpets which<br>can withstand 1-20 washings in water, for example,<br>precipitate of a mixture of oxides of tungsten and tin in<br>the soluble salts.<br>iii. Durable finishes. These retardants are very durable<br>and can import excellent antimony oxide with durable<br>functions to cotton fabrics, for example chlorinated<br>paraffin.<br>Most flame retardants contain elements from group III A,<br>(boron and aluminum) group VA (nitrogen, phosphorus,<br>arsenic and antimony) and group VII A (fluorine, chlorine<br>and bromine) [4].<br>Group III: A flame retardant which contain boron or<br>aluminum work by forming char which acts as a protective<br>layer that prevents oxygen from reaching the inner layers of<br>the material and thus sustaining the fire. Chemicals<br>commonly used for this purpose include borax, boric acid,<br>5</p><p>and hydrated aluminum oxide.<br>The group VA flame retardants work by forming a surface<br>layer of protective char. These include phosphoric acid,<br>diammonium orthophosphate and others, which are usually<br>applied in cellulose, polyester, and polyurethane products.<br>Arsenic is usually not used as flame retardant owing to its<br>toxicity, antimony in itself is ineffective as a flame retardant,<br>and it is used only in combination with halogens, especially<br>bromine and chlorine.<br>The group VII: A flame retardants which are the halogens<br>(Bromine, chlorine and fluorine). Bromine works as a flame<br>retardant in gaseous phase. When Bromine containing<br>compounds are incorporated into flammable materials, the<br>bromine dissociates from the material and form a heavy gas,<br>when the materials is exposed to flame. The dissociation<br>disperses heat and the bromine gas forms an insulating<br>layer around the material. The layer prevents flames from<br>spreading by inhibiting access to oxygen and by slowing the<br>transfer of heat. The use of these groups of fire retardants is<br>somehow restricted because of their environmental<br>6</p><p>implications. The flame retardants selected for the present<br>study are from group VA, which is incorporated in flexible<br>polyurethane form as a reactive not as an additive.<br>Polyurethanes are in the class of compounds called reaction<br>polymers, which include epoxies, unsaturated polyesters<br>and phenolics [5]. A urethane linkage is produced by<br>reacting an isocyanate group, -N=C=O with a hydroxyl<br>(alcohol) group, -OH. Polyurethanes are produced by the<br>poly-addition reaction of a poly-isocyanate with a<br>polyalcohol (polyol) in the presence of a catalyst and other<br>additives [6].<br>During the production, excess isocyanate groups in the<br>polymer with water or carboxylic acid produce carbon<br>dioxide that blows the foam. Foaming reactions occur in<br>three stages; the blow reaction lasts for about 12 seconds<br>and occurs as soon as isocyanate reacts with polyol to give<br>polyurethane and the polyurethane reacts further with<br>isocyanate to produce an allophanate in a reversible<br>reaction.</p><p>R1NHCOOR2 + R3N = CO R1N (CONHR3) COOR2<br>7</p><p>The rising time occurs when foam mix starts to rise until it<br>gets to a full block height. At this stage the isocyanate reacts<br>with water to generate carbon dioxide which causes the rise.<br>The formation of the carbon dioxide through the<br>intermediate carbamic acids gives.</p><p>RH = C = O + H – O – H RNH COOH RNH2 + CO2</p><p>The curing time is the reaction process that leads to<br>completion of the polymerization reaction that is usually<br>greater than 15 hours. Polyurethane can either be flexible or<br>rigid depending on the nature of the polymer and cross<br>linking produced. In the production of flexible polyurethane<br>foam, the polymerization reaction takes place between a<br>difunctional polyol and tolune diisocyanate. Flexible<br>polyurethane foams can be classified base on the density:<br>low density, 16-24 kg/m2, medium density, 32-48kg/m3 and<br>high density; 48kg/m3 and above [7].<br>The two basic types of flexible polyurethane foams are<br>polyester and polyether flexible polyurethane foams.<br>Polyesters are used mainly for clothing, interlining and<br>8</p><p>packaging while polyether are used to produced mattresses,<br>cushions and general upholstery [8]. Flexible polyurethane<br>foams can be produced in many grades of flammability,<br>elongation and load bearing capacities.<br>The level of flammability of the polyurethane foams is of<br>great concern both to the foam industries as well as whole<br>masses. In order to reduce the flammability of these<br>polyurethane foams, and hereby reducing the destructive<br>tendencies of fire outbreaks some suitable flame retardants<br>are incorporated into the foam. This study aims at<br>producing a flame retarded polyether flexible polyurethane<br>foam of melamine and tri ammonium orthophosphate in<br>various formulations.</p><p>1.2 Significance of the Research.<br>Flexible polyurethane foams are used in several applications<br>in homes, (mattresses, cushions), industries (automobile,<br>packaging etc); hence decrease in their flammability will<br>save lots of life and properties in event of fire outbreak in<br>these areas.<br>9</p><p>ï‚· Establishing the effects of using different concentration<br>of the applied fire retardants to the flexible<br>polyurethane foams will be valuable to commercial<br>foam manufacturers and researchers in the polymer<br>industry.<br>ï‚· Statistical establishment of the better fire retardants<br>out of the two on the fire characteristics of flexible poly<br>urethane foams will be useful to commercial foam<br>manufacturers.<br>ï‚· Comparison of the fire characteristics of flame retarded<br>polyurethane foams with the existing commercial<br>foams will clear the doubt of whether commercial<br>manufacturers actually incorporate fire retardants or<br>not.</p><p>1.3 Scope of the Study<br>* The study was based on only flexible polyether foams.<br>* The flame retardants incorporated in various<br>formulations are melamine, (C3H6N6) and tri<br>ammonium orthophosphate (NH4)3.(P04.3H20).<br>10</p><p>* The fire characteristics that were tested include: flame<br>propagation rate, ignition time, after glow time, % char<br>formation, and flame duration.</p><p>1.4 The objectives of the Study;<br>* The effects of melamine and triammonium<br>orthophosphate on the fire characteristics of the<br>flexible polyurethane foams were investigated.<br>* The fire characteristics of flexible polyurethane that<br>was flame retarded with melamine was compared with<br>that of flame retarded with triammonium<br>orthophosphate.<br>* The reduction of the flammability of the flexible<br>polyurethane foams was verified.<br>* The extent of the effects of the two flame retardants on<br>the ignition behaviour of flexible polyurethane foams<br>was established.</p> <br><p></p>