Polymer clay nanocomposites materials

Figure 15.1 Schematic picture ofa polymer-clay nanocomposite material with completely exfoliated (molecular dispersed) clay sheets within the polymer matrix material.

Polymer-clay nanocomposite materials can be prepared by intercalation of NVK into montmorillonite followed by the photoinitiated polymerization with a triarylsulfonium salt. ... 

Abstract The development of polymer-clay nanocomposite materials, in which nano-meter-thick layers of day are dispersed in polymers, was first achieved about 15 years ago. Since then, the materials have gradually become more widely used in applications such as automotive production. The first practical nylon-clay nanocomposite was synthesized by a monomer intercalation technique however, the production process has been further developed and a compound technique is currently widely used. A polyolefin nanocomposite has been produced by the compound method and is now in practical use at small volume levels. In this review, which focuses on njdon- and polyolefin-nanocomposites, detailed explanations of production methods and material properties are described. This article contains mainly the authors work, but aims to provide the reader with a comprehensive review that covers the works of other laboratories too. Lastly, the challenges and directions for future studies are included. 

The comprehensive flame retardation of polymer-clay nanocomposite materials was reported by Dr. Jeff Gilman and others at NIST [7]. They disclosed that both delaminated and intercalated nanoclays improve the flammability properties of polymer-layered silicate (clay) nanocomposites. In the study of the flame retardant effect of the nanodispersed clays, XRD and TEM analysis identified a nanoreinforced protective silicate/carbon-like high-performance char from the combustion residue that provided a physical mechanism of flammability control. The report also disclosed that The nanocomposite structure of the char appears to enhance the performance of the char layer. This char may act as an insulation and mass transport barrier showing the escape of the volatile products generated as the polymer decomposes. Cone calorimetry was used to study the flame retardation. The HRRs (heat release rates) of thermoplastic and thermoset polymer-layered silicate nanocomposites are reduced by 40% to 60% in delaminated or intercalated nanocomposites containing a silicate mass fraction of only 2% to 6%. On the basis of their expertise and experience in plastic flammability, they concluded that polymer-clay nanocomposites are very promising new flame-retarding polymers. In addition, they predict that the addition... 

It should be pointed out that many polymer/clay nanocomposite materials finally result in the formation of a mixture of exfoliated and intercalated structures [45], The above types of nanocomposites are schematically compared with an immiscible system in Fig. 3. 

Okada, A. and Usuki, A. 2006. Twenty years of polymer-clay nanocomposites. Macromolecular Materials and Engineering 291 1449-1476. 

Polymer-clay nanocomposites (PCN) are a class of hybrid materials composed of organic polymer matrices and organophilic clay fillers, introduced in late 1980s by the researchers of Toyota (Kawasumi, 2004). They observed an increase in mechanical and thermal properties of nylons with the addition of a small amount of nano-sized clays. This new and emerging class of pol miers has found several applications in the food and non-food sectors, such as in constmction, automobiles, aerospace, military, electronics, food packaging and coatings, because of its superior mechanical strength, heat and flame resistance and improved barrier properties (Ray et al., 2006). 

The term polymer clay nanocomposite (PCN) refers to a material composed of two-phase materials, where one phase (clay) is dispersed in the second phase (polymer matrix) at a nanometer level. Composites exhibiting structural and compositional changes at the molecular scale have demonstrated several physical property enhancements that are otherwise unavailable in conventional composites. Of these, layered silicates have proven themselves vital as a reinforcing agent when dispersed into engineering plastics. Nanolayers, however, are extremely difficult to disperse in polymer matrices because of their tendency for face-to-face... 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

Polymer clay nanocomposites are already used in many applications to enhance existing properties of a particular material, and development should be focused on the true multifunctional materials. Certainly, clay nanocomposites will continue to be used for enhanced mechanical, flammability, and gas barrier properties, but fundamental limits in clay chemistry prevent them from being used easily in applications requiring electrical/ thermal conductivity or optical properties. Similarly, combinations of... 

J.-M. Yeh, C.-P. Chin, and S. Chang, Enhanced corrosion protection coatings prepared from soluble electronically conductive pol3fpyrrole-clay nanocomposite materials, J. Appl. Polym. Sci., 88, 3264-3272 (2003). 

Y. H. Yu, C. Y. Lin, and J. M. Yeh. Poly(A-vinylcarbazole)-clay nanocomposite materials prepared by photoinitiated polymerization with triar-ylsulfonium salt initiator. J. Appl. Polym. ScL, 91(3) 1904-1912, February 2004. 

Okada, A., Usuki, A. Macromolecular Materials and Engineering Twenty Years of Polymer-Clay Nanocomposites. Macromol. Mater. Eng. 291, 1449-1476 (2006)... 

The reinforcement of polypropylene and other thermoplastics with inorganic particles such as talc and glass is a common method of material property enhancement. Polymer clay nanocomposites extend this strategy to the nanoscale. The anisometric shape and approximately 1 nm width of the clay platelets dramatically increase the amount of interfacial contact between the clay and the polymer matrix. Thus the clay surface can mediate changes in matrix polymer conformation, crystal structure, and crystal morphology through interfacial mechanisms that are absent in classical polymer composite materials. For these reasons, it is believed that nanocomposite materials with the clay platelets dispersed as isolated, exfoliated platelets are optimal for end-use properties. 

Yeh, J.-M., et al. 2002. Enhancement of corrosion protection effect of poly(o-ethoxyaniline) via the formation of poly(o-ethoxyaniline)-clay nanocomposite materials. Polymer 43 (9) 2729. 

In the last few decades, polymeric materials have found many applications and govern a major part of our day-to-day life. The polymeric materials are strong, lightweight, and easily processable with cost-effective techniques [1]. However, the properties of the pure polymeric materials limit their application in diversified fields. The introduction of filler materials into the polymer matrix generates properties superior to those of individual components. The combination forms a single system the polymer nanocomposites exhibit improved strength, stiffness and dimensional stability with adequate physical properties compared to pure ploymer. These nanocomposites can be of different types such as ceramic-based nanocomposites, fiber-reinforced nanocomposites, polymer-clay nanocomposites, etc. 

T. J. Pinnavaia, and G.W. Beall, Polymer-Clay Nanocomposites, Wiley, 2000. G.A. Sotirou, C.O. Blattmann, and S.E. Pratsinis, Advanced Functional Materials, 23,1616,2013. 

Unlike polymer-clay nanocomposites, in rubber-clay nanocomposites complete exfoliation of clay layers results in disappearance of the diffraction maxima in their XRD patterns. However, this can also occur due to other reasons, like extremely low concentration of clay materials in the composites, crystal defects, etc. The majority of the reports on rubber-clay nanocomposites display the intercalated or swollen nature of the clay structures. The presence of the basal reflections in the XRD patterns of such type of nanocomposites indicates that the clay crystal structure is not destroyed completely. But, shifting of their positions to lower 26 values is interpreted as an expansion of the interlayer region by the macromolecular rubber chains. Besides, broadening of the characteristic reflections in nanocomposites is often related to the defects in the crystal layer stacking caused by the interlayer polymeric species. 

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