Layered-silicate polymer composites

Fig.1 Schematic illustration of different possible structures of layered silicate polymer composite (a) microcomposite (b) intercalated nanocomposite (c) exfoliated nanocomposite [12]...

Y.-W. Mai, Z.-Z. Yu Ed. Polymer Nanocomposites. CRC Press, Baton Roca, PL, USA 2006. ISBN 9780849392979 a review by an international team of authors with 13 papers on layered silicates/polymer compositions and eight papers on nanotubes, nanoparticles and inorganic-organic hybrid systems. 

The nano-scale structures in polymer layered-silicate nano-composites can be thoroughly characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD is used to identify intercalated structures. XRD allows quantification of changes in layer spacing and the most commonly used to probe the nano-composite structure and... 

Alexandre, M. and Dubois, P. 2000. Polymer-layered silicate nano-composites preparation, properties and uses of a new class of materials. Materials Science and Engineering 28 1- 63. 

Ray, S.S., Bousmina, M. Biodegradable polymers and their layered silicate nano composites In greening the 21st century materials world. Prog. Mater Sci. 50(8), 962-1079 (2005)... 

Due to recent improvements in visualization of nanoscopic material with enhanced resolution, huge advances in the characterization technology have been widespread in all the nanotechnology disciplines, compared to just about 20 years ago. A few examples of nanoscopic materials that are less than Ipm are illustrated in Figure 1.2. Current efforts in the nanoparticle—polymer field go into very small metallic and semiconductor nanoparticles with 1—2nm diameter, and use of micron-sized fillers (e.g., layered silicates) (Polymer-Nanoparticle Composites Part 1 (Nanotechnology), 2010). 

Coiai, S., Scatto, M., Bertoldo, M., Conzatti, L., Andreotti, L., Sterner, M., Passaglia, E., Costa, G., and Ciardelli, R 2009. Study of the compounding process parameters for morphology control of LDPE/layered silicate nano-composites. e-Polymers, no. 050 1-18. http Hwww.e-polymers.org/ journal/papers/scoiai 280509.pdf... 

Lu, C.S. Mai, L.W. (2007). Permeability modeling of polymer-layered silicate nanocomposites. Composites Science and Technology, 67, 2895-2902... 

PBA-SS nanocomposites were synthesized by a novel, cost-effective, unconventional emulsifier-free emulsion technique. The XRD results showed a disordered layer structure due to intercalation of polymer into the layered silicate. These composites were further characterized by TGA, TEM and their burning rates and exhibited improved properties of thermal stability with good fire retardant properties. It is found that the fire retardant nanocomposites have average biodegradability and have promising future prospects. 

The intercalation of organic cations enhances the interlayer distance resulting in delamination and exfoliation of the silicate layers. However, a homogeneous dispersion and distribution of exfoliated silicate layers in polymer composites is easy to realize with polar polymers but more difficult to achieve in unpolar polymers such as olefins. After proper surface modification and exfoliation of the silicates the general nanocomposite manufarturing techniques later discussed in this chapter can be applied. However, depending on the type... 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

Polymer layered-silicate day nano-composites (PLCN) attracted lately major interests into the industry and academic fields, since they usually show improved properties with comparison by virgin polymers or their conventional micro and macro-composites. Improvements induded increase in strength, heat resistance (Giannelis, 1998), flammability (Gilman, 2000) and a decrease in gas permeability (Xu et ah, 2001) as well as an increase in biodegradability (Sinha et al., 2002). 

However, the field of polymer day silicate has only started to speed up recently, mixing the appropriate modified layered silicate with synthetic layered silicates has long been known (Theng, 1979). The interest in these materials came from two important findings, first has been reported by Toyota research group of a Nylon-6 (N6)/Na-MMT nano-composites (Okada et ah, 1990) where very small amounts of layered silicate loadings resulted in the improvements of thermal and mechanical properties and second the findings of Vaia et ah (1993) about the... 

Three main types of composites can be formed when the layered clay is incorporated with a polymer, as shown in Figure 2 (Alexandre and Dubois, 2000). Types of composites formed mostly depend on the nature of the components used (layered silicate, organic cation and polymer matrix) and the method of preparation. 

Of particular interest are the recently developed nanocomposites consisting of a polymer and layered silicate because they often exhibit remarkably improved mechanical and other properties [3] when compared with pure polymer or conventional composites (both micro- and macro-composites). A primary progress in... 

Report 162 Analysis of Thermoset Materials, Precursors and Products, Martin J. Forrest, Rapra Technology Ltd Report 163 Polymer/Layered Silicate Nanocomposites, Masami Okamoto, Toyota Technological Institute Report 164 Cure Monitoring for Composites and Adhesives, David R. Mulligan, NPL... 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

Moreover, the development of new strategies for surface modifications of nanoparticles with compounds having FR activity could provide a new field of research on FR systems. The use of novel phosphorus-, nitrogen-, or halogen-containing modifiers, instead of alkylammonium ions, for layered silicates seems promising. FR action conferred by the surface modifier can be combined with action due to composite morphology, particularly when the host polymer is a polymer blend instead of a pure polymer. 

Experimental results obtained allow to mark a promise of this research direction. Developing new polymer composite materials based on natural layered silicates and polyethyleneterephthalate - the most needed polymer material - gives opportunity to modify PET properties and therefore expand the field of its application. 

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

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