Epoxy nanocomposites based on cationic clays

Epoxy resins are, by and large, the most investigated resins for the preparation of nanocomposite systems, and for this reason they are used as a case study in this chapter. The principles illustrated for this specific system can be generalized for other thermosetting resins. 

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Thermosetting nanocomposites exhibit a reduced rate of heat release compared to neat polymer. However, the approach to nanocomposites itself is not sufficient to comply with the actual fire test standards. For this reason, traditional flame retardants are currently used in combination with nanofillers, and researchers are focusing on the individuation of synergistic systems. As an alternative to the most common cationic clays, anionic clays show improved performance in terms of flame retardancy. Epoxy nanocomposites based on anionic clay exhibit unique self-extinguishing behavior in a UL-94 horizontal burning test never observed before in a pure nanocomposite. The formation of a continnous intu-mescent ceramic layer on the surface of a polymer during combustion reduces the heat release rate to a higher extent than do montmorillonite nanocomposites. 

Thermal Decomposition of Polymeric Nanocomposites Based on Anionic Clays The thermal decomposition of DGEBA nanocomposites cured with polyoxypropylene diamine (Jeffamine D230) and containing 4-toluenesul-fonate/LDH was investigated by simultaneous thermal analysis (STA) in air. The LDH nanocomposite (TS/LDH) is compared to the neat epoxy and to a bis(2-hydroxyethyl)ammonium montmorillonite nanocomposite (30B). The clay content was 5 wt% for both nanocomposites. In Figure 9.24, differential thermal analyses obtained by STA are shown. A main exothermic peak is observed at about 550° C for neat epoxy. In the LDH nanocomposite this peak is split in two parts, so the heat release rate is decreased and the heat evolution delayed, where as no relevant difference is observed between neat epoxy and the cationic clay nanocomposite. 

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