Encapsulation of Clay

The encapsulation of the clay in the miniemulsion droplets/particles has attracted considerable interest in the academic field. 

However, some groups have claimed the successful encapsulation of MMT platelets inside polymer particles.In all three cases cited it is more than 

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Figure 3.1 Schematic representation of the challenges in encapsulation of clay platelets through emulsion polymerization and related techniques.

In this chapter, we focus on three areas of research the use of nascent clay as the stabilizing agent in direct emulsion polymerization, the use of hydro-phobized clay as the stabilizing agent in inverse emulsion polymerization and encapsulation of clay by means of emulsion polymerization processes. 

One of the main goals of academic research is the encapsulation of organically modified clay in miniemulsion droplets and, upon polymerization, in latex particles. In order to achieve this, it is necessary to have only droplet nucleation and to avoid secondary nucleation. There are examples in the literature of encapsulation of inorganic particles via miniemulsion polymerization, but there is no clear evidence of successful encapsulation of clay or only under limited conditions (low solids content, high surfactant loading) in papers devoted to miniemulsion polymerization of waterborne polymer-clay nanocomposites. 

The possible morphologies that can be created during the sonication process are depicted in Figure 10.1. There are two thermodynamically stable cases regarding the clay location, namely the preferential location at the droplet surface (Figure lO.le) and full encapsulation (Figure 10.1a). The first case is desirable when solid particles instead of surfactant molecules are used to stabilize a (mini)emulsion and one speaks of a Pickering (mini)emul-sion. The latter case of encapsulation of clay platelets into the latex particles is preferred when surfactant molecules are used to stabilize the (mini)emulsion. 

As shown in the simulation of the morphology of hybrid monomer-clay miniemulsion droplets (Figures 10.2 and 10.4), the encapsulation of clay platelets is possible provided that the clay/water interfacial tension is very high (superhydrophobic clay) and that the clay/monomer interfacial tension is low (high compatibility between clay and monomer). Another aspect that the simulations show is that the size of the clay platelets might also play a role in the encapsulation of the clay in the monomer droplets (polymer particles). 

The method of action of the polymers is thought to be encapsulation of drill cuttings and exposed shales on the borehole wall by the nonionic materials, and selective adsorption of anionic polymers on positively charged sites of exposed clays which limits the extent of possible swelling. The latter method appears to be tme particularly for certain anionic polymers because of the low concentrations that can be used to achieve shale protection (8). 

In these systems, particularly systems such as potassium chloride polymer, the role of bentonite is diminished because the chemical environment is designed to collapse and encapsulate the clays since this reaction is required to stabilize water-sensitive formations. The clay may have a role in the initial formulation of an inhibited fluid to provide the solids to create a filter cake. 

Encapsulation of herbicides within anionic clays was readily identified by the loss of HRMAS NMR signal associated with immobilization of the molecules between clay layers.103 The application of HRMAS to soil samples has been shown to provide important results on the interaction of herbicide and other organic components with the soil matrix, using ID lH HRMAS, selective TOCSY and 2D TOCSY experiments.104 Significant advantages to the HRMAS approach are its reduced samples preparation needs, with no extraction, pre-treatment or purification required. 

Solidification The physical encapsulation of contaminants in clays, cement, or other solid binders so that they may undergo safe disposal in the environment (such as landfilling). In contrast, stabilization refers to the immobilization of contaminants through the formation of chemical bonds between the contaminants and the binders. Solidification and stabilization simultaneously occur in waste treatment and are commonly called solidification/stabilization. 

Earlier reports [50] showed that vesicles composed of oleic acid can grow and reproduce as oleoyl anhydride spontaneously hydrolyzed in the reaction mixture, thereby adding additional amphiphilic components (oleic acid) to the vesicle membranes. This approach has recently been extended by Hanczyc et al. [51], who prepared myristoleic acid membranes under defined conditions of pH, temperature, and ionic strength. The process by which the vesicles formed from micellar solutions required several hours, apparently with a rate-limiting step related to the assembly of nuclei of bilayer structures. However, if a mineral surface in the form of clay particles was present, the surface in some way catalyzed vesicle formation, reducing the time required from hours to a few minutes. The clay particles were spontaneously encapsulated in the vesicles. The authors further found that RNA bound to the clay was encapsulated as well. 

The encapsulation of pigment and filler particles is an important area of research, both in the academic world and in industrial laboratories. At present, emphasis is given to the incorporation of clay in polymeric materials, including polymeric nanoparticles. Such systems are expected to exhibit properties other than the sum of the properties of the individual components. In general, several benefits from this encapsulation step can be expected when the obtained particles will be applied in a polymeric matrix (e.g., plastics or emulsion paints) as compared to physical blends ... 

In a different approach, the [Mn(salhd)Cl] complex was immobilised onto an Al-WYO PILC by simultaneous encapsulation of the complex and pillaring of the clay with aluminium polyoxocations. Two distinct routes were followed method A - simultaneous pillaring/encapsulation, with addition of the [Mn (saZen)X] complex after the oligomeric species formation, and method B - simultaneous pillaring/encapsulation, with addition of the complex to the initial clay dispersion. The heterogeneous catalysts... 

UPE resins can be used as clear castings or in combination with particulate fillers or fibres. The resin was developed to meet the demand of lightweight materials in military application. The first functional use of UPE was in radome. Because of the obvious advantages of easy processability and low cost, it was used in a wide range of applications in civil sectors such as tanks, pipes, and electronic gears. Some of the important products based on cast UPE resins are encapsulation of electronic assembly, buttons, door handles, knives, umbrellas, industrial wood and furniture finishing. A filled resin system using limestone, silica, and china clay are used for floor tiles. The major use of UPE is as a matrix for fibre-reinforced composites. Such composites have wide applications in automobile and construction industries such as boats, water-skis and television antennae. Examples of applications of UPE resins are presented in Table 2.7. 

Tactoid/agglomerate - polymer chains encapsulate stacks of clay platelets. 

Talc is a naturally occurring magnesium silicate which is finding broad application as a filler in polyolefins. Apparently, it provides a moderate flame retardant effect, but because talc is inexpensive, it is used as a partial substitute for more expensive flame retardants. Fumed silica is used as a filler in epoxy resins for the encapsulation of electronic devices at a relatively high loading, np to 80 to 90 wt%. Because of the relatively small amount of combnstible resin, this composition can be flame retarded by the addition of a very small amonnt of a conventional flame retardant. It is not clear if the silica contribnles to the flame retardancy by any mechanism other than heat dispersion. Nanodis-persed clay, which is one of the main topics of this book, is an alnminosiUcate. The mechanism of its flame retardant action is discnssed in other chapters of the book. 

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