**6.1 Common nano fillers**

Nano carbons are chemically modified, for example, dCOOH functionalized to improve physical bonding with polymers. The reinforcing effect of single-wall carbon nanotube (SWCNT) is much higher than multiwall tubes (MWCNT) because of higher specific surface area.

Graphene and graphene oxides are a new class of plate-type reinforcing nanoparticles, having layer of single graphitic plates, can be physically bunched as 3–8 layers. Graphene is an allotrope of carbon whose structure is a single planar sheet of sp2 bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The graphene can have a spacing of 0.3–0.5 nm between two platelets. Graphene is purer form of carbon, having no organic impurities or functional groups attached, hence their bond with polymers is less intensive than other allotropes of carbon nanoparticles. However, synthesis of graphene from graphite/ carbon leads to graphene oxide, which is more polar and can have better bonding with polar resins, which are used for FRP.

Clays are layered silicates, with complex crystal structures. There are different naturally occurring clays such as bentonite, which is kind of rock, mixture of different minerals, including smectite (2:1 layered clay), montmorillonite (dioctahedral), hectorite, (tri-octahedral). The clays are organically modified, for example, ion exchanged with quaternary alkyl ammonium salts, to allow an oligomer molecule to enter in the clay gallery, thus intercalating or even exfoliating the clay. Cloisite is a class of montmorillonite clay, commercially available in various hydrophobicities, and is in the order: Cloisite 15A > 20A > 25A > 10A > 93A > 30B > Cloisite Na<sup>+</sup> . Typical clay gallery spacing in montmorillonite (Cloisite) is about 1–1.9 nm depending on their structure, and the spacing is increased upon modification and is further exfoliated or intercalated when a low-molecular-weight polymer enters the clay gallery. Typical surface area of a montmorillonite nanoclay of 75–150 nm transverse size is approximately 750 m2 /g.
