PREPARATION AND CHARACTERIZATION OF LAYERED DOUBLE HYDROXIDES BASED POLYMERIC NANOCOMPOSITES
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M. Zammarano[*],1,M.C. Moore, J.W. Gilman,1 Richard H. Harris1, John R. Shields1
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1 BFRL, NIST, 100 Bureau Drive, Gaithersburg, MD 20899-8665, USA 1 blank line between affiliations and text Layered double hydroxides (LDH), also known as anionic or hydrotalcite-like clays, have lately been used for the preparation of polymeric nanocomposites . LDH are rare in nature, but can be readily synthesized. They have a layered structure with aspect ratios similar to, or even higher, than the ones observed for aluminosilicate clays: the layers are 0.48 nm to 0.49 nm thick and their planar dimensions reach 20 mm . Important features of LDHs are the highly tunable intra-layer and inter-layer composition that allow one to fit the properties of the clay to applications in a large number of fields (catalysis and their supports, adsorbents, ceramic precursors, electrochemical reactions, stabilizers and gene therapy).
Nano-dispersed Layered Double Hydroxides allow combining the flame retardant mechanisms of both inorganic hydroxides (endothermic decomposition, ceramic residue formation, dilution of evolved combustible gases, decrease of CO/CO2 ratio) and layered crystal nanocomposites (barrier effect, synergistic effect with traditional FR, charring reactions) . It was already demonstrated that in epoxy resin LDHs based nanocomposites show a higher flame retardant properties compared to aluminosilicate clays nanocomposites . The formation of an intumescent continuous char with an intercalated nanostructure significantly decrease the PHRR (peak of heat release rate) compared to montmorillonite based nanocomposites.
High throughput techniques are used for the synthesis of the organo-modified LDH by high shear co-precipitation (colloid mill), as well as for the monitoring of the dispersion (through co-intercalated fluorescent anionic dye), and the FR properties (flame spread test).
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