Intumescent systems

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

Caze, C., Devaux, E., Testard, G., and Reix, T., New intumescent systems An answer to the flame retardant challenges in the textile industry, in Fire Retardancy of Polymers The Use of Intumescence, Le Bras, M., Camino, G., Bourbigot, S., and Delobel, R. (Eds.), 1998, Royal Society of Chemistry, London, pp. 363-375. 

As the polyol-based char formers needs to be substituted, Li and Xu40 reported the synthesis of a novel char former for intumescent system based on triazines and their derivatives. It is a macromo-lecular triazine derivative containing hydroxyethylamino, triazine rings and ethylenediamino groups (Figure 6.7). They showed that the new char former in an intumescent formulation containing APP... 

FIGURE 6.7 Synthesis of macromolecular triazines derivatives as char former for intumescent systems. (From Li, B. and Xu, M., Polym. Deg. Stab., 91, 1380, 2006.)... 

Tang et al.84,85 also examined the incorporation of MMT in intumescent PP with a compatibilizer (hexadecyltrimethylammonium bromide) which is usually used as surfactant for making OMMT. Evidence of making a nanocomposite is shown with and without the intumescent system. Cone calorimetry shows a large improvement in the flammability properties when using OMMT. The results are similar to what we showed above. They postulated a mechanism of action suggesting the formation of an aluminophosphate structure but no evidence was given. 

The use of synergists (micro- and nanoparticles) was also investigated in intumescent coatings. The most recent work conducted is based on the studies done in intumescent bulk polymer (see reaction to fire part). Li et al.108 suggested combining EG and/or molybdenum disilicide (MoSij) in an intumescent system based on APP/PER-melamine. The results show that incorporating the... 

In this chapter, we have discussed recent developments of intumescent flame-retarded materials in terms of reaction and resistance to fire. Research work in intumescence is very active. New molecules (commercial molecules and new concepts) have appeared. Nanocomposites are a relatively new technology in the held of flame retardancy. This technology gives the best results combined with conventional FRs and leads to synergistic effects with intumescent systems. Very promising developments in the synergy aspects are then expected and efforts should be continued in this way. 

Morice, L., Bourbigot, S., and Leroy, J.M. 1997. Heat transfer study of polypropylene-based intumescent systems during combustion. J. Fire Sci., 15 358-374. 

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. 

In an attempt to provide compatibility between the FR and polymer matrix, Wang et al. reported recently on a novel microencapsulated intumescent system containing 4A zeolite as a potential flame retardant for natural rubber (NR).61 The flame-retardant properties of NR composites loaded with different amounts of intumescent flame retardant (IFR), IFR-4A zeolite, and microencapsulated intumescent flame retardant (MIFR)-4A zeolite agents were studied and compared. The LOI data demonstrate that the NR composite filled with 50phr of MIFR-4A zeolite agent and 50phr of IFR-4A zeolite shows better FR properties as compared to NR and 50phr of IFR-filled systems. 

Melamine diborate (MB), known in the fire-retardant trade as melamine borate, is a white powder, which can be prepared readily from melamine and boric acid. It is partly soluble in water and acts as an afterglow suppressant and a char promoter in cellulosic materials. Budenheim Iberica79 claims that, in a 1 1 combination with APP, MB (10%-15%) can be used for phenolic bound nonwoven cotton fibers. In general, melamine borate can be used as a char promoter in intumescent systems for various polymers including polyolefins or elastomers. However, its low dehydration temperature (about 130°C) limits its application in thermoplastics that are processed at above 130°C. Melamine borate is also reported to suppress afterglow combustion in flame-proofing textiles with APP or monoammonium phosphate to meet the German DIN 53,459 and Nordtest NT-Fire 002.80... 

This approach has been followed in the case of APP/PER (Pentaerythritol) systems, with or without zeolite (such as 4A zeolite for example), in order to better understand the synergistic effect of these aluminosilicate fillers in polyolefin-based intumescent systems.15... 

As an example, Marosi et al.21 have followed this approach to investigate the effect of surface and interface modifications in intumescent systems including MMT nanoparticles. The formulations... 

Fire-retarded materials functioning in the condensed phase, such as intumescent systems, form, on heating, foamed cellular charred layers on the surface, which protects the underlying material from the action of the heat flux or the flame. It is recognized that the formation of the effective char occurs via a... 

The study of the viscosity of intumescent systems appears, as a consequence, to be an important way to better understand the carbonization process. The data obtained from this technique agree and complement the results obtained during the examination of the chemical composition of the intumescent shield. Moreover, it has to be highlighted that, to the contrary of most of the chemical investigations of the carbonization process, this technique studies the material in situ whereas most of the charred chemical compositions are evaluated after combustion and cooling of the sample. 

Whatever the formulations, curve of the rate of heat release versus time shows two peaks, the first before 200s 0,) and the second between 300s (REF) and 500s (OMMT), which is the typical behavior of intumescent systems. The first peak is attributed to the formation of the intumescent protective shield that leads to a decrease in heat and mass transfers between the flame and the material. When this shield is formed, the RHR decreases and a plateau is observed in some cases. The second peak corresponds to the destruction of the intumescent layer leading to a sharp emission of flammable gases, the higher the time for the second peak, the higher the thermal and mechanical stabilities of the intumescent shield. Then, a thermally stable residue is formed. When lamellar... 

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. 

Duquesne, S., Le Bras, M., Jama, C., Weil, E.D., and Gengembre, L. 2002. X-ray photoelectron spectroscopy investigation of fire retarded polymeric materials Application to the study of an intumescent system. Polymer Degradation and Stability 77(2) 203-211. 

Duquesne, S., Lefebvre, J., Bourbigot, S., Le Bras, M., Delobel, R., and Recourt, P. 2004. Nanoparticles as potential synergists in intumescent systems. Paper Presented at the ACS 228th Fall National Meeting, Division of Polymeric Materials, Science and Engineering, Session—Fire and Materials, Philadelphia, PA. 

Layered Silicates in Intumescent Systems Based on Ammonium... 

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