Nanosized clays

A recent report by Fan et al. [267] claimed that the incorporation of nanosized clay modified with quaternary ammonium salt in polypropylene imparted dyeability. The technique... 

The TEM images of the surface of the nanocomposites can help to find out the degree of the distribution of the nanosized clay particles, see plots (a) to (d) in the Figure 9. 

Inorganic carbohydrate hybrid systems - Limited information is available on the use of saccharides in nanostructured inorganic hybrids. Some papers describe the incorporation of nanosized clays in thermoplastic starch by exfoliation 21-22), Recently the synthesis of starch/clay superabsorbents was reported (23). Several studies concern the preparation and properties of organo-silicon derivatives and cellulose-based hybrids (24-25). Inorganic starch hybrids with electrorheological activity were prepared using in situ sol-gel synthesis... 

Nanocomposites are a new class of particle-filled composites in which at least one dimension of the dispersed particles is within 100 nm. Because of the dispersion of nanosize clay particles, polymer-clay nanocomposites exhibit improved moduli and strength, decreased thermal expansion coefficient, decreased gas permeability, increased swelling resistance, better thermal stability and enhanced ionic conductivity when compared to the pristine polymers or microscale composites [149-151], They find increased applications in various fields such as automobile, packaging, electronic, coating and aerospace industries [152,153],... 

Nanoparticles combined with other nanoparticles of other materials or with larger bnlk-type materials are termed as composites. Nanoparticles, such as nanosized clays, have already been added to prodncts ranging from anto parts to packaging materials to enhance their mechanical, barrier, thermal, and flame-retardant properties. 

Nanosized sulfated tin oxide (STO) particles dispersed in the micropores of Al-pillared clay (STO/Al-P), were used by Mishra and co-workers [91] as an environmentally benign, recyclable and efficient catalyst for the solvent-free synthesis of 3,4-dihydropyrimidin-2(l//)-ones 42 using a domestic microwave oven. The protocol offers advantages in terms of simple experimentation, reusable catalyst, excellent yields, short reaction times, and preclusion of toxic solvents (Scheme 31). 

Sowmiya M, Sharma A, Parsodkar S et al (2007) Nanosized sulfated Sn02 dispersed in the micropores of Al-pillared clay as an efficient catalyst for the synthesis of some biologically important molecules. Appl Catal A Gen 333 272-280... 

Although there is much current excitement about nanomaterials, there is really nothing new about nanoscience. In fact, the earliest civilizations used nanoscale materials for a variety of applications. For example, the Mayans used a magnesium aluminum silicate clay called palygorskite, which contained nanosized channels that were filled with water. The Mesopotamian civilizations used colored glass for decorative applications that contained embedded metallic nanoparticles. 

These are by far the most commonly used systems for the formulation of insoluble solids. The solid can be hydrophobic, such as most organic materials that are used in pharmaceuticals, agrochemicals, and paints the solid can also be hydrophilic, such as silica and clays. With some pigments and inks the particles need to be very small - that is, in the nanosize range - and these are referred to as nanosuspensions. Latexes may also be considered as suspensions, particularly if the particles are solid-like at ambient temperatures. With many of the latexes that are used in paints the particles are liquid-like at below and ambient temperature, but when applied to a surface these liquid-like particles coalesce to form a uniform film. The system may then be considered as an emulsion. 

In the LB technique, a monolayer of amphiphilic molecules, prepared at the air-water interface, is transferred to a substrate, thus giving a monomolecular film. The molecules must be solvable in a volatile, water-insoluble (organic) solvent, but not, or to a very limited extent, in water. Thus, when the solution of the molecules in the organic solvent is spread over the surface of water, the solvent evaporates, leaving a monolayer of molecules at the air-water interface. This monolayer can be compressed and transferred to a substrate. When the molecules are replaced by colloidal, nanosized particles, monolayers of these particles on a substrate are obtained. Smectites are especially well suited for the LB technique. The elementary clay sheets are about 1 nm thick and a few tens to hundreds nm wide and long. In the alkali- or alkaline earth form, they are hydrophilic, but by ion exchange with suitable amphiphilic cations, they become hydrophobic. There are then two ways to prepare mono-layers of smectite clay particles by the LB technique. 

Nam et al. [44] studied the detailed crystallization behavior and morphology of pure PLA and one representative PLA/C18-MMT nanocomposites. They concluded that the overall crystallization rate of neat PLA increases after nanocomposite preparation with C18-MMT. These behaviors indicate dispersed MMT particles act as a nucleating agent for PLA crystallization in the nanocomposites. Lee and co-workers ([45]) who investigated the thermal and mechanical characteristics of PLA nanocomposite scaffold, reported that the recrystallization temperature (Tc) of quenched PLA and its nanocomposite systems decreased by the addition of MMT clay. The nanosized layered MMT platelets provide large surface area due to their small size and thus it is reasonable to consider that the MMT particles could act as effective nucleating sites of PLA crystallization. The increased nucleating sites are likely to facilitate the PLA crystallization process in the nanocomposite systems. 

The mechanical properties of fire protecting interfacial film are essential for the final stability level of the W/0 emulsions. Concentrated polymeric interfacial films may display either elastic or viscous properties that make the destabilization process difficult and time consuming. The aromatic asphaltene molecules will normally undergo a stacking into sandwich-like structures as a consequence of tire molecular association. The presence of other nanosized-particles like organic wax particles and inorganic clay particles will further enhance the stability level. However, fliese compounds are not further dealt wifli in the present chapter. 

Figure 28 shows the relationships between the amount of inorganics in the clay and the gas permeability coefficient. The gas permeabiUty coefficient decreased as the amount of added clay increased. The gas barrier performance of PPCN-5 increased by 1.7 times. It has been reported that the barrier performance of the nylon-clay nanocomposites and polymer-clay nanocomposites was improved. This barrier effect is explained as being attributed to the geometrical detour effect of the dispersed nanosized silicates. The barrier effect of PPCN, however, was smaller than that of the nylon-clay nanocomposites. hi the case of the nylon-clay hybrid, the addition of 1.8 wt % of mont-morillonite caused its hydrogen permeability to decrease to 70%. In the case of PPCN, about 3 wt % of montmorillonite must be added to obtain the same... 

Three different types of nanomaterials, based on their dimensional characteristics, are generally used to prepare polymer nanocomposites. These include nanomaterials with only one dimension in the nanometre range (e.g. nano-clay), those with two dimensions in the nanometre scale (e.g. carbon nanotubes) and those that have all three dimensions in the nanometre scale (e.g. spherical silver nanoparticles), as stated earlier. Thus nanosize thin layered aluminosilicates or nanoclays, layer double hydroxide (LDH), a large number of nanoparticles of metals and their oxides, carbon nanotubes and cellulose nanofibres are used as nanomaterials in the preparation of vegetable oil-based polymer nanocomposites. 

In the last two decades, polymer nanocomposites have attracted the interest of researchers and industries because of their excellent mechanical, physical and tribological properties. The addition of nanosize inorganic fillers like clay, Al Oj, CaCOj, TiOj, ZnO and SiO has altered the mechanical and physical properties of the polymers significantly, and in general the nanocomposites are superior to virgin polymers in many aspects. 

As a second example, consider the liquid/solid interface in a nanosized environment representative of the interlayer space of clay minerals. The hydrophilic and swelling properties of these minerals is the result of structurally induced perturbations of acid-base chemistry in nanosized spaces. 

CB is often used together with other fillers to get obtain hybrid fillers to further enhance NR properties. Liu et al. added nanosized CB and poly(ethylene glycol) (PEG) modified clay to prepare NR nanocomposites. They suggest that NR with hybrid fillers exhibits superior mechanical properties compared to NR with CB as the sole filler. Rattanasom et al also reported that the tensile strength and elongation at break increase from 15.3 to 25.4 MPa and 460 to 605%, respectively, for the CB-filled NR as compared to NR with hybrid fillers (CB and modified clay). 

Sharif et reported that NR/OC nanocomposites were prepared by melt blending using electron beam irradiation as a substitute for sulfur. It was found that the physical and mechanical properties of radiation-induced crosslinking of NR composites with OC were improved due to the presence of nanosize intercalated silicate layers in the NR matrix. Replacing sulfur with radiation-induced crosslinking of NR/OC nanocomposites was not significantly affected by the amount of OC up to 10 phr. Meanwhile, the thermal stability of NR/OC nanocomposites improved with an increase in clay content up to 10 phr. 

Fillers such as CaCOs, clay, etc. with average particle size in the range 01 to 100 nm may be defined as nanofillers. Unlike traditional fillers, mainly used for cost reduction, nanofillers are performance-enhancing fillers used in relatively small amounts (5 10%) in order to provide substantial improvements in physical and other properties. Nanosized particles (average diameter around 40 nm) form a very fine and homogeneous distributed system in polymer matrix. As compared to micron size filler particles the nanosized filler particles are able to occupy substantially greater number of sites in the polymer matrix. 

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