Intumescent systems additives

X-ray diffraction (XRD) has been poorly used to characterize the carbon phase of intumescent structure. Indeed, as shown previously, the carbon structure resulting from the development of the intumescent system is mainly disordered whereas XRD characterizes ordered structure. However, this technique may be of interest to study the carbonization process in the case of flame-retardant systems containing layered additives, such as expandable graphite,28,42 or even more in the case of lamellar nanocomposites, such as MMT-based nanocomposites. 

Further possible additives include aliuniniiun hydroxide, magnesium hydroxide and magnesium carbonate. Intumescent systems are increasingly promoted when a halogen free system is requested. 

Organic peroxides fail to increase the rate of crosslinking of deacetylated units. Better results are obtained with the addition of an intumescent system. This is a combination of melamine phosphate and phosphate-phosphonate substituted trimethylamine. The EVA is shown to play a substantial role in the intumescence phenomenon, thus complementing the zinc borate work in France. 

Intumescent flame retardants (IFR) that contains phosphorus are also used in halogen-free flame-retardant systems. Most reported IFRs are mixtures of the three ingredients, an acid source, a polyol, and a nitrogen-containing compound (Halpem et al. 1984). Since processing of ABS resin requires that the additives withstand temperatures in excess of 200 °C, the commonly used intumescent system, ammonium polyphosphate, pentaerythritol, and melamine, which do not have sufficient thermal stability, cannot be incorporated into ABS resin under normal processing conditions they are usually used in polyolefins. 

Other plastics additives, especially colorants, need to be carefully screened. Certain organic pigments such as phthalocyanine blues or greens are known to interfere with intumescent systems. 

The intumescent approach has been used for about 50 years in coatings for the protection of metal and wood structures [1,2]. The introduction of intumescent systems in the bulk of polymeric materials is relatively recent [3-5]. The early developments in intumescent additives for polymers were based on experience acquired in coating applications. Indeed, the empirical approach had led to a recognition of the need for compounds capable of supplying the charred residue (a carbonific ) and of blowing it to a foamed cellular structure ( spumific ) as components of formulations showing intumescent behaviour in coatings. 

The use of a single additive overcomes the difficulty encountered by having two or three components of traditional intumescent systems, which have to diffuse within the polymer matrix until they collide and react. This approach might however reduce the fire retardant effediveness. 

In this section we have demonshated that intumescent systems provide efficient fire retardant properties to polymeric materials, both in bulk and as a coating. The mechanisms of action have been discussed and we have seen that the chemistry of such systems offers some flexibility in the synthesis of the char (e.g., potential reactivity of phosphates and oxidized functions). We can then expect to enhance the performance of the intumescent char by the addition of other reactive compounds in the formulation, which is the purpose of the next section. 

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