Flame retardant finish - Fire Proof

Flame Retardant finish - part-3.

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:
1: 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 1/4th to ½ 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.
Author: C.N.Sivarama Krishnan
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