Nano-clays intercalates

The intercalation of nano-gold into clay layers comprised two steps. The first step was the intercalation of the polymer (surfactant) into clay matrix for increasing the interlamellar space between the clay layers. The second step was the replacement of the intercalated polymer (surfactant) by Au nanoparticles by adding different amounts of nanoparticles to the polymer (surfactant)/clay composite. Both steps were performed by applying ultrasonic irradiation. The solution was sonicated at 20 kHz, 500 W. The intercalation progress was monitored as a function of time. The precipitated nano-Au/intercalated product was separated by centrifugation, washed with water and dried under vacuum overnight. After that samples were calcined in air at 800 °C for 4 h. 

Lan and Pinnavaia [6] showed that hybrid organic-inorganic composites exhibited mechanical properties superior to those for their separate composites. Dependence of tensile strength and modulus of epoxy nano-clay composites on the chain length of the clay-intercalated alkylammonium ions is shown in Fig. 28. The presence of the organoclay substantially increased both the tensile strength and modulus relative to the pristine polymer. The mechanical properties increased with any exfoliation in the order ... 

Nano-clay particles, 476 Exfoliated, 476 Intercalated, 476 Nanoclay, 190... 

The soluble polymers can be intercalated into the galleries using this method. Polymer is dissolved in the solvent containing the desired weight fraction of nano-clay. The polymer chains intercalates into the interlayer spacing of the clay platelets. The nanocomposite is formed by the evaporation of the solvent. This method is good for the intercalation of polymers... 

The impact strength of clay-polymer nanocomposites either increases, decreases or remains unaltered by the nano-clay incorporation. The impact strength is not altered much by the presence of nano-clay, as reported elsewhere [21]. A special co-intercalation type of organoclay was used. In another study, an improvement in impact property is noticed while incorporating nano-clay in PP matrix [58]. The Izod impact strength of PP and CPN is shovm in Figure 9.37. 

Nano-clay composites contain very thin, high aspect ratio, alumino-silicate platelets, derived from the stacks present in the parent clay. Two types of stmcture can be recognised, intercalated and delaminated. In the intercalated form, the stacks of platelets are still present, but with polymer chains present between clay platelets, pushing them apart. In the delaminated form, the original stacks are no longer present, and the platelets are fully dispersed. 

The principal effects observed in cone calorimeter tests are a marked reduction in peak and average rate of mass loss and in heat release. There appears to be little reduction in total heat of combustion or in smoke levels. The workers at NIST report that there seems to be little difference between intercalated and delaminated forms of nano-clay, despite evidence that polymer thermal stability can be more improved by the intercalated structure. 

Figure 10.6 High resolution electron micrograph of a cross-section of a nano-clay/ polypropylene composite illustrating some intercalated, partly dispersed clay stacks (tactoids) Micrograph kindly supplied by Monica Celotto)...

The same situation exists for nano-clays, but is complicated by the presence of surface-active species used in their preparation. These organic treatments comprise a significant part of most nano-clays, and fulfil a number of very important functions. Thus, they increase the gallery spacing, making it easier for other species, such as monomers or polymers, to intercalate. The increased spacing also makes it easier to disperse, or delaminate the structure. In the simplest cases, these intercalants would also provide the compatibility and interaction with the polymer matrix described previously. It is thus obvious that the nature and amount of intercalant have to be chosen carefully and controlled. For ease of treatment, it is also helpful for the intercalant to be water soluble. 

These effects were obtainable with only 3-5 % by weight of additive, but did not change much when higher loadings were used. While not firmly established, present results indicate that both intercalated and delaminated forms of the same nano-clay have similar effects. This is perhaps surprising, given that the delaminated form is by far the best gas barrier. 

Inoue and Hosakawa have shown good effects in a number of polymers using melamine intercalated into nano-clay structures [48]. 

Figure 15.1. Transmission electron microscopy images of polypropylene filled with nano-clay to 5 wt%. (a) The combination of exfoliated and intercalated clay platelets is evident, (b) After stretching the platelets appear to be less curved and ai e aligned in the stretch-direction...

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22], A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofdler in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24]. 

Micro-composites are formed when the polymer chain is unable to intercalate into the silicate layer and therefore phase separated polymer/clay composites are formed. Their properties remain the same as the conventional micro-composites as shown in Figure 2(a). Intercalated nano-composite is obtained when the polymer chain is inserted between clay layers such that the interlayer spacing is expanded, but the layers still bear a well-defined spatial relationship to each other as shown in Figure 2(b). Exfoliated nano-composites are formed when the layers of the day have been completely separated and the individual layers are distributed throughout the organic matrix as shown in Figure 2(c). 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

Layered clay nano composites have been prepared by melt intercalation for a variety of polymers, including polystyrene [221], nylon-6 [222], ethylene-vinyl acetate copolymers [223], polypropylene [224], polyimide [225], poly(styrene-fo-butadiene) [226], and PEO [227],... 

In practice, the techniques of blending, compositing and nano-reinforcement are often used together. Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites exhibited the intercalated and exfoliated structures [260]. Mont-morillonite (MMT) with three types of cation or modifier (Na", alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties, in comparison with pristine MMT. 

Layered siUcate/polypropylene nanocomposites were prepared by melt intercalation method. Homopolymers PP alone and maleic anhydride-grafted polypropylene (PPgMA) as a compatibiUzer were used as the matrix. Clay (Na montmorillonite, MMT) particles were used to obtain silicate nano-layers within the PP matrix. Structural modification of MMT... 

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