Nano clays

Nano clays are used as fQlers in thermoplastics and thermosets. The nano clay maybe combined with another chemical ingredient, such as a crosslinking agent, to thereby provide a imique and overall S5mergistic effect on mechanical property performance (13). 

A number of techniques have been described for dispersing the inorganic layered material into a polymer matrix. It has been suggested to disperse individual layers, e.g., platelets, of the layered inorganic material, throughout the polymer. However, without some additional treatment, the polymer will not infiltrate into the space between the layers of the additive sufficiently and the layers of the layered inorganic material will not be sufficiently uniformly dispersed in the polymer. 

Currently there is much interest in the use of nano-clays as flame retardant additives for polymers. The topic has recently been reviewed by Porter and co-workers [51]. Present understanding is not well developed, but Gilman and co-workers at NIST are carrying out an extensive study of the area [52, 53]. Commercial applications are also starting to appear [54]. 

The production and characteristics of nano-clays are covered in Chapter 2 of the present work. Their uses in polymers, including further discussion of fire retardant effects, are the subject of Chapter 10. Some aspects of their compounding are dealt with in Chapter 5. 

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. 

The primary effect of the nano-clays seems to be related to char formation. The workers at NIST have found that a reduction in mass loss and heat release rate only starts once the surface of the polymer is at least partly covered by char. Beyer reported that, while no char was produced by burning unfilled EVA, the filled composite formed a strong char early in the process [54]. Once the amount of clay is taken into account, final char levels are often similar to unfilled polymer, indicating that while a stronger, more insulating, char may form and retard combustion, it is eventually consumed in this test. 

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Figure 9.27 shows the TEM micrograph of the cell wall foamed at 100 °C under 28 MPa. Interestingly, the grown cells with a diameter of 200 nm are localized along the dispersed nano-clay particles in the cell wall. In other words, the dispersed nanofiller particles act as nucleating sites for cell formation and the cell growth occurs on... 

Another approach utilizes highly oriented pyrolytic graphite that is separated into individual graphite sheets as the inner layer material. In each case, the nano-clay or graphite material is present in about 2% by weight in the tire inner liner. 

Hussain M, Varley RJ, Mathys Z, Cheng YB, Simon GP. Effect of organo-phosphorus and nano-clay materials on the thermal and fire performance of epoxy resins. J. Appl. Polym. Sci. 2004 91 1233-1253. 

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 ... 

Y.H. Lee, T. Kuboki, C.B. Park, and M. Sain. Processing-property behaviors of PP/rice hull and PP/rice hull/nano-clay composites. In The Global Outlook for Natural Fiber Wood Composites, Intertech, Portland, ME, Lake Buena Vista, FL, 2005. 

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

As an alternative to harmful fire retardant, nano-clay applications have recently been nsed very successfully, especially with PU foams that are used in furniture [23]. A draft list of Persistent, Bioaccumulative, and Toxic substances, providing limits under the proposed EU-REACH regulations for authorisation (targeted for control and/or substitution) in the short-term, as well as elimination in the longer term, is also available. 

Wang T, Colver PJ, Bon SAP, Keddie JL (2009) Soft polymer and nano-clay supracol-loidal particles in adhesives synergistic effects on mechanical properties. Soft Matter 5(20) ... 

Abstract. Polyvinylalcohol (PVA) is a polymer soluble in hot water, it has the property of film formation and it can improve the concrete performance. The effects of PVA modified with nano clay on the cement hydration reaction have been investigated by means of semiadiabatic calorimeter, FTIR spectroscopy and SEM. FTIR spectroscopy was employed to monitor chemical transformation of cement. The morphology of the different samples was compared by means of SEM micrographs. With the semiadiabatic calorimeter the hydration kinetic was measured to compare the heat rate of the admixtures materials. Fixing the water-cement ratio, w/c, in 0,45, the ratio of polymer to cement (p/c) was 2 wt% and the ratio of clay to polymer was 4 wt% (0.8wt.% related to cement). The polymer and modified polymer admixtures produced a retardation effect on the kinetic of cement hydration, but the clay acts as nucleating agent. The increase of the temperature with time was measured and a new model with four parameters was employed and the kinetic parameters were determined for each sample. 

The effective methods currently available for separating agglomerations will promote the application of nano-fillers such as nano-clay. Because the dimensions of these particles are smaller than the wavelength of light, there is a marked reduction in light scattering, thus enhancing transparency. 

Hassan Nejad, M., Ganster, J., Bohn, A. et al. (2009) Bio-based nanocomposites of cellulose acetate and nano-clay with superior mechanical properties. Macromolecular Symposia, 280, 123-129. 

Hassan Nejad, M. (2011) Improving the Mechanical Properties of Polysacchtiride Derivatives though Melt Compounding with Nano-Clays. PhD thesis, Technische Universitat Beriin. http //opus.kobv.de/ tuberlin/volltexte/201 l/3042/pdf/hassannejad mehdi.pdf (accessed 22 June 2013). 

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. 

G. Das and N. Karak, Mesua ferrea L. seed oil based amido-amine modified nano-clay/epoxy nanocomposites ,/Appl Polym Sci, 2012,124,2403-13. 

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 DSC curves for thermoset epoxy with different weight fraction of organo-modified nano-clay are shown in Figure 9.11. The onset temperature of the curing and the temperature of the exothermal peak for neat resin are 115°C and 155 C, respectively. The addition of 5 wt% nano-clay in epoxy matrix reduces the onset temperature to 84°C and peak exothermal temperature to 143°C. The catalytic effect of the nano-clay on the crosslinking reaction of epoxy resin is responsible for the reduction. 

Figure 9.12 shows the impact of nano-clay incorporation on the melting and crystallization temperatures of polypropylene. 

Figure 9.27 shows the influence of nano-clay incorporation on storage modulus of the epoxy nanocomposites. The increase in percentage of nano-clay in epoxy resin increases the storage modulus up to a certain weight fraction of nano-clay, above which it decreases the modulus, but it is still above the value of neat epoxy matrix. The loss modulus curve shows the variation of glass transition temperature with respect to nanoclay incorporation and the maximum value of glass transition temperature is noted for the clay content of 3 wt% [31]. 

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. 

The incorporation of dimethyl-dialkyl ammonium treated montmoril-lonite clay does not alter the impact toughness in sub-zero temperatures, whereas the addition of nano-clay improves the strength at higher temperatures. However, the fracture toughness of nanocomposites and neat epoxy increases when they are treated with sea water for 180 days. The... 

Polymer nanocomposites find their first application in car hoods, which are easily attacked by NO pollutants since they are exposed to the exterior environment. NO at standard atmosphere and pressure is 29.5% NO and 70.5% N O. Polyamide-6 is highly sensitive to such pollutants. The infusion of nano-clay platelets in the polyamide matrix in general decreases the diffusivity and permeability of the nanocomposites to atmospheric oxygen... 

The water absorption behavior of the clay-epoxy nanocomposites in terms of maximum water uptake and diffusion coefficient are given in Table 9.18 [47]. The presence of nanoparticle as reinforcement reduces the water absorption of the composite system. The maximum water uptake of epoxy decreases gradually with the increase in clay content. The maximum water absorption decreases by 14.1,17.9 and 24.8% after the incorporation of 1, 3 and 5 wt% nano-clay, respectively, compared with neat epoxy. The presence of high aspect ratio nanofillers can create a tortuous pathway for water molecules to diffuse and enhances the resistance to water absorption. The diffusivity also decreases in the same manner and a significant reduction in diffusivity is obtained for the composites containing 5 wt% clay [112]. 

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