Intumescent materials

C. Paone, Preventing Cook-Off with Intumescent Materials, Army RD A Bulletin, Jan.—Feb. 1990. 

One possible solution to the problem is to make greater use of intumescent materials which when heated swell up and screen the combustible material from fire and oxygen. Another approach is to try to develop polymers like the phenolic resins that on burning yield a hard ablative char which also functions by shielding the underlying combustible material. 

Intumescent materials, which are water-based systems, cure by evaporation. If applied during periods of high humidity, the areas of application may experience blistering when the humidity drops and the evaporative curing continues. In such environments, solvent-based materials are recommended. 

An extensive study was conducted on the effect of chemical and structural aspects of zeolites on the fire performance of the intumescent system, ammonium polyphosphate-pentaerythritol (APP-PER), where a marked improvement of the fire-retardant properties within different polymeric matrices has been observed.56 58 The synergistic mechanism of zeolite 4A with the intumescent materials was investigated using solid-state NMR. Chemical analysis combined with cross-polarization dipolar-decoupled magic-angle spinning NMR revealed that the materials resulting from the thermal treatment of the APP-PER and APP-PER/4A systems were formed by carbonaceous and phosphocarbonaceous species, and that the zeolite enhances the stability of the phosphocarbonaceous species. 

Duquesne, S., Le Bras, M., and Delobel, R. 2002.Visco-elastic behavior of intumescent materials. Thirteenth Annual BCC Conference on Fire Retardant, Stamford, CT, June. 

The comparison between the 7, values of the two systems (Figure 10.5) shows that their behavior compared to HTT is different. At 280°C, the 7 , value of the system with the zeolite is twice as large as that for the APP/PER system. It was concluded that the materials formed at this temperature are structurally different. Indeed a slower 7) means that the molecular motions may be hindered and therefore that the structure may be more rigid. Between 280°C and 350°C, the Tx values decrease and become identical. At 350°C, both systems are organized in stacks of polyaromatic species and it may be proposed that the two materials are structurally, in the NMR sense, similar. At higher temperatures, the 7 , values of the systems with zeolite are always larger. The carbonization process of the two intumescent materials develops in different ways. The zeolite allows molecular motion and the carbonaceous shields keep mobile structures. 

So, the viscoelastic properties of intumescent materials in the range of temperature corresponding to the development, the stabilization, and the destruction of the protective shield are, as a consequence, an important task of investigation. The way to investigate those parameters is detailed in Section 10.4.1. 

Bourbigot S, Leroy J-M. Modelling of thermal diffusivity during combustion—application to intumescent materials. In Fire Retardancy of Polymers The Use of Intumescence. Le Bras M, Camino G, Bourbigot S, Delobel R, Eds. The Royal Chemical Society Cambridge, U.K., 1998 pp. 129-139. 

Kay M, Price AF, Lavery I. Review of intumescent materials, with emphasis on melamine formulations. J. Fire Retard. Chem. 1979 6 69-91. 

Camino G, Lomakin S. Intumescent materials. In Fire Retardant Materials. Horrocks AR, Price D, Eds. Woodhead Publishing Cambridge, U.K., 2001 chap. 10, pp. 318-336. 

In carpets, the intumescent layer can be applied between the tufting and the backing, or on the upper surface of the backing. The intumescing material also closes up the interstices of the fire-exposed fabric. Nylon carpets made with this backing are fire retardant and are said to meet airline standards for fire safety.26... 

The sueeess of graphite in this applications shows that filler with plate like struetures should be considered when intumescent materials are being formulated. Reeent developments in intumescent paints show that performanee ean be improved if a layer of organic material is inserted between the layers of the plate like filler. The degradation of this material in the enclosed space increases the expansion rate and the retention of gas inside the degrading material. Based on this prinei-ple any plate like filler has the potential to be useful in an intumescent applieation. The eomposition of filler is also important. When clay was used as a filler in fire retardant applieations, it was found that some of its components interfere with the action of carbonization catalysts and detract from the overall performance of the system in terms of limiting oxygen index. ... 

Figure 5.31 shows a eurve typieal of the performance of intumescent material. The degradation proeess should oeeur rapidly which generates an insulation layer in a short period of time and keeps the temperature of adjaeent layers suffieiently low to prevent their degradation. In the graph, the height of peak is important sinee it shows the amount of retained material. 

Firstly there are forms of polymers, such as polytetrafluoroethylene, which are intrinsically fire retardant. The second types are rendered fire retardant by the inclusion of a suitable additive in the formulation. These include additives based on antimony, bromine, nitrogen, phosphorus and silicon. An essential requirement for fire retardant polymers used in enclosed spaces is that they do not release any toxic products upon combustion. Ffowever, antimony containing additives are going out of favour due to the release of toxic antimony volatiles upon combustion. The properties and mechanisms by which these polymers operate are discussed in Chapters 1 and 6. The third group of polymers consist of intumescent materials and these are being increasingly used as a means of imparting fire retardancy in polymers and this is discussed in Chapter 7. 

Another solution to improve the fire-retardant (FR) properties of polymers is the use of intumescent additives [2, 3]. Intumescent technology [4, 5] has found a place in polymer science as a method of imparting flame retardancy to polymeric materials. On heating, FR intumescent materials form a foamed cellular charred layer on their surfaces [6, 7], which protects the underlying materials from the action of heat flux and flame. The proposed mechanism [8] is based on the charred layer acting as a physical barrier, which retards heat and mass transfer between the gas and the condensed phase. 

In order to understand the fire behaviour of the EVA-APP/PA-6 formulation, Le Bras and co-workers [50] deal with the chemical characterisation of the intumescent materials formed during combustion in the conditions that occur in a cone calorimeter. 

The application of intumescent materials to textile materials has been reviewed - and is exemplified in the patent and research literature by the following examples ... 

A property of a material which swells when heated/(a material able to swell during heating, forming an insulating protective layer over the substrate). Intumescent materials are used as fireproofing agents. 

It is a support for acidic catalytic species which react with the oxidized products formed via the thermooxidative degradation of the material. So, the intumescent material consists of polyaromatic stacks bridged by polymer links and phosphate (poly-, di- or orthophosphate) groups, as presented in Figure 5. 

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