The field of flame retardancy has witnessed a vigorousdevelopment of new technologies and new products and materials to meet thechallenge of the needs of new industries-such as computer, electronics andtelecommunication industries. Flame retardants are also used in health caresettings, Intravenous pumps, hospital beds Hospital curtains.. An additionalchallenge is the growing awareness of environmental issues and the stiffeningdemands of consumer safety, which has been put forward by governments and publicagencies. New flame-retardant systems are needed to meet the new product and market demands.

New regulations, standards and testing methods, as well asinstruments, are essential for assessing and defining these needs. These newregulations present new challenges to the flame-retardancy industry. With newfibers /blends rapidly changing the economic situation, today manufacturerneeds to be fully aware of new regulations and the products and processes that will meet them. Companies that adopt the latest technology will have the edge in providing superior products with the best balance of properties at the lowestpossible price Synthetic polymers have largely replaced the use of wood, Glassand other metallic materials in our homes, offices, automobiles and otherpublic areas. These synthetic materials are often petroleum based plastics thateasily ignite, spread flames quickly and release toxicants when burned.

Fire safety is a significant cause of property damage and ofdeath. Standards are therefore set for electrical appliances, textilesupholstery and many other materials to minimize these losses. To meet firesafety standards, products made of synthetic materials are modified with flameretardant chemicals that inhibit the ignition and spread of flames. Recently,there has been a great deal of interest in providing effective flame retardantsfor normally flammable substrates. For example, there is great interest in thedevelopment of flame retardant finish on synthetic fibers like polyester, nylon,polypropylene etc, without disturbing the desirable physical characteristics ofthe fibers. Textiles consist of highly ignitable materials and are the primary source of ignition. They contribute to rapid fire spread; however, reduction ofignitability can be obtained by

1: Use of Inorganic materials {Asbestos, Glass etc}

2: Through chemical treatment with FR {Flame Retardantchemicals}

3: Through modification of the polymer.

Function of a Flame Retardant:

Flame retardants are chemicals are applied to fabrics toinhibit or suppress the combustion process. They interfere with combustion atvarious stages of the process e.g. during heating, decomposition, ignition offlame spread. Fire is gas phase reaction. For a substance to burn, it mustbecome a gas. As with any solid, a textile fabric exposed to a heat sourceexperiences a temperature rise. If the temperature of the source (eitherradiative or gas flame) is high enough and the net rate of heat transfer to thefabric is great, pyrolytic decomposition of the fiber substrate will occur. The products of this decomposition include combustible gases, non combustiblegases and carbonaceous char. The combustible gases mix with the ambient air andits oxygen. The mixture ignites, yielding a flame, when its composition andtemperature are favorable. Part of the heat generated within the flame istransferred to the fabric to sustain the burning process and part is lost tothe surroundings.

Mechanism of Flame Retardancy

Flame retardant systems for synthetic or natural polymers can act physically and/or chemically by interfering at particular stages of burning

By cooling Endothermic processes triggered by the flame retardants cool the substrate.

By forming a protective layer: The heat transfer is impeded, fewer pyrolysis gases are evolved, and the oxygen is excluded.

By dilution.: Substances, which evolve inert gases on decomposition, dilute the fuel in the solid and gaseous phases. The concentrations of combustible gases fall under the ignition limit.

Reaction in the gas phase: The free radical mechanism of combustion processes which takes place in the gas phase could be interrupted by flame retardants.

Reaction in the solid phase: One mechanism is the accelerated breakdown of polymers.

Types of Flame Retardants:

Brominated flame retardants

Chlorinated flame retardants

Phosphorous-containing flame retardants {Phosphate ester such as Tri phenyl phosphate

Nitrogen-containing flame retardants (i.e. Melamines)

Inorganic flame retardants.

These can be further classified as:

Inorganic, Organo Phosphorous, Halogenated organic and Nitrogen based compounds.

2: Halogenated organic flame retardants are further classified as containing either Chlorine or Bromine {Brominates Flame Retardants BFR}

There are three types BFRs currently produced. These are Poly Brominated DiPhenyl Ethers {PBDE}, Tetra Bromo Bisphenol A {TBBPA} and Hexa Bromo Cyclodecane {HBCD} The PBDEs that are commonly used in products are Deca, Octa, and Penta BDE .The concentration of BFRs in products ranges from 5 to 30 % .Compounds containing Iodine are known, but of limited utility as flame retardants, due to their poor thermal stability and dark colour of iodine. Compounds containing Fluorine generally exist as functional polymers rather than materials to be added to other polymeric systems to provide flame retardancy. These polymers are oxidatively stable and only decompose at very high temperature.

Antimony oxide is another important component flame retardant composition, containing halogen, particularly Chlorine and Bromine. It is totally ineffective if used with out halogen. The Tri oxide is the common material used although the Pentoxide can also use. The pentoxide has a much finer particle size and is more effective per unit weight added than the trioxide. Polyesters are very sensitive to residual acidity in all forms of antimony oxide. Alkaline salts of antimony oxides are used in these critical cases. Antimony oxide acts as synergists with chlorine and bromine.

Antimony tri bromide is a dense white product and is one of the main components of the typical white smoke that is seen from burning polymers containing halogen and antimony oxide. High levels of water from normal combustion cause reversion of SbBr3 to HBR and Sb203.The remaining antimony oxide is then available to react with fresh HBR from decomposing brominated compound. Typically compounds used in flame retardant application contain either 40 to 70 % Chlorine or 45 to 80% Bromine, depending on the flame retardant requirements from 20 to 40 parts of Brominated compound would be used per 100 parts of polymer. Antimony oxide used is typically 1/4^th to that of the halogenated material.

Many of the flame retardants do not remain on the fabric, instead they slowly leak from the products in the atmosphere. Brominated flame retardants are a subject of scrutiny. Evidence shows that they are likely to persist in the environment, bio accumulate in the food chain and finally in to our bodies. A survey of the newer flame retardants suggests a simple theory for their constitution. The molecule should be water-insoluble to achieve durability in laundering. A solvent-soluble organic molecule will give better results. The ortho-phosphate group should be present in the molecule to dehydrate catalytically the cellulose substrate. The molecule should contain polymerizable groups to effect a permanency of finish. The molecule should contain halogen or other groupings to reduce the flammability of the gases of decomposition.

When chemical free alternative materials or designs are not feasible, non halogenated flame retardants can be used to meet fire safety standards. Numerous alternatives are available. It is also confirmed that flame retardants based on Aluminum Trioxide, Ammonium Polyphosphates and Red phosphorous are less problematic in the environment.

Application on Textiles:

One of the most preferred processes of applying FR on cotton is the "Precondensate"/NH₃ process. This is an application of one of several phosphoniums "precondensates," after which the fabric is cured with ammonia, then oxidized with hydrogen peroxide Precondensate is the designation for a Tetrakis-hydroxymethyl phosphonium salt pre-reacted with urea or another nitrogenous material. The amount of anhydrous sodium acetate is approximately 4% of the amount of precondensate used. Some precondensates are formulated along with the sodium acetate. Softeners are also added along with precondensates.

The pH of the pad bath should be approximately 5.0.The amount of flame retardant required depends primarily on fabric type, application conditions, and test criteria to be met. Screening experiments should be conducted to determine the minimum application level for a fabric. Application of FR to fabric can be accomplished with conventional padding, padding with multiple dips and nips, followed by 30 to 60 seconds dwell gives good results. A critical factor in the successful application of precondensate/NH₃ flame retardant is control of fabric moisture before ammoniation. Generally, moisture levels between 10% and 20% give good results.

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