Alumina nanofillers

In the case of alumina nanofillers inside the silica matrix, the adhesion between particles and the matrix appears to be stronger. Therefore, there is low interfacial cracking and no increase in the fracture energy due to an increase in fracture surface area is observed. This situation leads to constant values of fracture energy in terms of nanofiller content. 

Ogunniran ES, Sadiku R, Ray SS, Luruli N. Effect of boehmite alumina nanofiller incorporation on the morphology and thermal properties of functionalized poly(propylene)/polyamide 12 blends. Macromol Mater Eng 2012 297 237 8. 

G. Beyer, Flame retardant properties of EVA-nanocomposites and improvement by combination of nanofillers with alumina trihydrate, Fire Mater., 2001, 25 193-197. 

Of particular interest to adhesives formulators are nanofillers such as carbon nanotubes (CNT), silica, alumina, magnesium oxide, titanium dioxide, zirconium oxide (Zn02), silver, copper, and nickel). Of these, carbon nanotubes are the most widely studied for electrically conductive adhesives to attach microdevices, to interconnect microcircuits and to increase I/O densities at the device level. ... 

Other filler materials are hydroxyapatite, aluminum oxide and aluminum nitride. In addition, nanofillers are used. PEEK polymer filled with nano sized silica or alumina fillers of 15-30 nm exhibit an improvement of the mechanical properties by 20-50%. The agglomeration tendency can be somewhat dimiiushed by a modification of the surface of the fillers with stearic acid. °... 

Hollow tubes extracted from the silica/alumina clay halloysite exist naturally as particles roughly 500 nm long, and they do not have the exfoliation issues of platy nanoclays. Thus, these nanofillers do not require the same specialized equipment and processing that nanoclays require for proper dispersal. As fillers, nanotubes provide high properties because of their very high aspect ratios. 

There is an improvement in strength by 15% and modulus by 40% for the alumina nanoparticle concentration of 10 vol% by retaining its strain at failure compared to the neat epoxy [79]. The addition of nanofillers may not increase the brittleness of the epoxy since the nanoparticles being fine in size (50-500 nm), which may not act as stress raiser. Instead they induce some mechanism that allows the deformation process rather than constraining the matrix. 

Nanoclay fillers are categorized as platelet-like nanoclays or layered silicates and tubular nanoclays in terms of filler shape. With the configuration of two tetrahedral sheets of silicate and a sheet layer of octahedral alumina, platelet-like nanoclays or phyllosilicates are formed, which include smectite, mica, vermiculite, and chlorite. In particular, smectite clays are widely employed with further subcategories of MMT, saponite, hectorite, and nontronite. The typical MMT clays are regarded as one of the most effective nanofillers used in polymer/clay nanocomposites due to their low material cost and easy intercalation and modification (Triantafillidis et al., 2002). On the other hand, the fundamental structure of tubular nanoclays contains an aluminum hydroxide layer and a silicate hydroxide layer. They are also known as dio-ctahedral minerals with two different types of halloysite nanotubes (HNTs) and imo-golite nanotubes (INTs). Notwithstanding their material role as clay minerals, these two types of tubular nanoclays resemble the hollow tubular structure of carbon nanotubes (CNTs). In this section, three different types of clay nanofillers, namely MMTs, HNTs, and INTs are reviewed in detail along with the development of clay modification. 

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