This article presents a brief but concise review of the current research efforts on polymeric nanocomposite foams production, characterization, and applications. Survey indicates that the emergence of nanocomposites has resulted in the development of a new group of materials regarded as nanocomposite foams. Nanocomposites result from the use of nano-sized (10-09 m) particles as fillers to modify and enhance the properties of polymers and other matrices. The combination of functional nanoparticles and foaming technologies such as supercritical fluid foaming, chemical foaming, syntactic foaming, aerogel foaming, phase inversion foaming etc. generate these new materials regarded as nanocomposite foams that have light weight, high specific strength, and multifunctional attributes. Enhanced thermo-mechanical properties of nanocomposite foams result from improved cell morphology that is mainly attributable to the role of nanoparticles as nucleation agents for bubble generation. High-specific mechanical properties and multifunctional characteristics of nanocomposite foams make them cost-effective and desirable in a multitude of application areas including structural, energy-dissipating/absorbing, acoustical insulation, flammability resistance, and others. Of particular importance in this study of nanocomposite foams is the flammability resistance effect of nanoparticles. The intumescent model (NIST, NMAB, and others) indicates that the flame barrier mechanism involves a high-performance carbonaceous-silicate char; this char build-up insulates the underlying material. Understanding this char build-up mechanism presents a challenge and area of research interest in the effort to develop new generation foams that are suitable in energy absorbing materials and structures.
Current aerospace and naval applications require blast and flammability resistance characteristics. Materials and formulations with flammability resistance properties are most suitable in these type applications since fire and smoke toxicity are inherently associated with blast situations. In this effort, VAHLUP fabricated epoxy nanocomposites are evaluated and characterized for flammability resistance properties such as effective heat of combustion, ignition time, rate of mass loss, rate of heat release and smoke density. The effects of nanoparticles on the mechanical properties of epoxy nanocomposites are also evaluated. Uncoated polyaramid papers (Kevlar, Nomex with heat release rates of 0.18, 0.175 MJ/m2 respectively) exhibit better flammability resistance properties than resin/nanocomposites coated polyaramid papers. VAHLUP fabricated epoxy nanocomposites exhibit better flammability resistance properties than cast epoxy nanocomposites. Kapton, polyimide film with ignition time of 90 seconds+] give the best overall flammability resistance properties. Mechanical properties of epoxy nanocomposites are enhanced by processing. The preliminary data of the influence of the post-curing protocol tend to suggest the 2.0% nanoclay level as the optimal clay content level with respect to mechanical properties.
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