Mechanism of flame retardancy

Attempts to disrupt this cycle for textile substrates have focused on several approaches. One method is to provide a heat sink on or in the fibre by use of materials that thermally decompose through strongly endothermic reactions. If enough heat can be absorbed by these reactions, the pyrolysis temperature of the 

Another approach is to apply a material that forms an insulating layer around the fibre at temperatures below the fibre pyrolysis temperature. Boric acid and its hydrated salts function in this capacity (Fig. 8.4). When heated, these low melting compounds release water vapour and produce a foamed glassy surface on the fibre, insulating the fibre from the apphed heat and oxygen. 

Type of chemistry involved Pyrolysis chemistry Flame chemistry 

Effective for fibre type Mainly cellulose, also wool, catalysing their dehydration to char All kinds of fibres, because their flame chemistry is similar (radical transfer reactions) 

Particularities Very effective because dehydration and carbonisation decrease the formation of burnable volatiles Fixation with binder changes textile properties such as handle and drape, preferably for back coating, for example of furnishing fabrics and carpets 

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D. Price, Y. Liu, G.J. Milnes, T.R. Hull, B.K. Kandola, and A.R. Horrocks, An investigation into the mechanism of flame retardancy and smoke suppression by melamine in flexible polyurethane foam. Fire Mater., 26, 201-206 (2002). 

It has been reported that the effectiveness of copolymerized DOPO-type monomers can be further improved if the alcohol-amine derivatives of DOPO, for example, Structure 5.11, are used rather than similar structures not containing nitrogen.30 Of the FR fibers based on P-containing comonomers, it has been found that those based on Structure 5.10 are more hydrolytically stable, presumably because the P-containing group is in a cyclic structure and also should the hydrolysis of the P-0 bond occur, it will not lead automatically to a marked reduction in molecular weight.31 All the P-modified PETs appear to be subject to both the vapor-and condensed-phase mechanisms of flame retardance, with the former predominating.32 33... 

A predominantly vapor-phase mechanism of flame retardation has been proposed for flame retardants based on triphenylphosphine oxide and triphenyl phosphate has been proposed (Scheme 5.1). 

Hornsby, P.R. and Watson, C.L., A study of the mechanism of flame retardancy and smoke suppression in polymers filled with magnesium hydroxide, Polym. Deg. Stab., 30, 73-87,1990. 

Wang, J., Mechanism of flame retardancy in polyamides containing magnesium hydroxide, Ph.D. thesis, Brunei University, London, U.K., 1994. 

Lewin M. Physical and chemical mechanisms of flame retarding of polymers. In Fire Retardancy of Polymers. The Use of Intumescence. Le Bras M, Camino G, Bourbigot S, Delobel R, Eds. Royal Society of Chemistry London, 1998 pp. 3-32. 

Chemical modification of polymers by the addition of various flame retardants may have different effects on the ignitability of polymeric materials. Information about such effects helps to explore certain features of the activity mechanism of flame retardants... 

The leading mechanisms of flame retardance of polymers may be related to physical or chemical effects at any stage of the combustion. As a rule, the chemical influences (characterized by the rate constants of the respective reactions) are closely interrelated with the physical ones (characterized by heat- and mass-transfer parameters). Establishing the role of each factor and estimating its individual contribution to the overall effect is important for the development of ways of reducing the flammability of polymeric materials. 

The folowing features are used as macroscopic criteria of the activity mechanisms of flame retardants... 

Many theories attempt to explain the mechanism of flame retardancy. The flame retarding action is thought to take place in the vapor phase above the burning surface. For antimony oxide to work, the halogen and antimony oxide must be found in a vapor phase which will occur at temperatures above 315°C. At these temperatures, antimony halides and oxyhalides are formed and act as flame extinguishing moieties by quenching radicals as they form. 

Thermal Degradation Mechanisms of Flame-Retarded Polyesters... 

The results of cone calorimetric tests lead to the conclusion that char formation plays a key role in the mechanism of flame retardation for nanocomposites. This could be explained by the specific antioxidant properties and high thermal conductivity of MWCNT which determine high performance carbonization during thermal degradation process. 

Studies of the mechanisms of flame-retardance occupy a wide circle of re-searchers. ... 

Vijayakumar, C. T. and Fink, J. K. Investigations on the mechanism of flame retardancy, in HET-acid containing unsaturated polyester resins. J. Appl. Polym. Sci., 27, 1629 (1982)... 

Small amounts of PTFE, added to several polymers that are flame retarded with antimony-bromine systems, can significantly improve their flame retardancy. The chemical reaction between PTFE and Sb20s leads to the evolution of volatile Sb-containing species which, however, are not responsible for the whole mechanism of flame retardancy as the improvement requires all components to be involved the polymer, the bromine system and, of course, the PTFE. It has been found that SbFs is the species of greatest interest since it is likely to be formed in high temperature reaction between PTFE and antimony trioxide. 

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