Clay reinforcement nanocomposites

An alternative method of producing natural rubber based clay reinforced nanocomposites with outstanding properties is by using a spray drying technique. In this technique the siUcate layers of clay will be well dispersed in an irradiated polymer latex and this mixture will be sprayed through hot air to produce micrometre-sized liquid droplets. When the solvent is fully evaporated, micrometre-sized polymer spheres with delaminated clay silicate layers on their surface are produced. These spheres can later be melt blended with natural rubber to produce ternary nanocomposites. It is noteworthy that exfoliation of nanofillers can still be achieved without modification of the nanofiller surface, thus the expensive modification process can be eliminated. 

For clay-reinforced nanocomposites, increases in modulus compared with the unfilled polymer matrix have been observed in many systems with the effect increasing with filler content as expected but the properties are highly sensitive to microstructure (Luo and Daniel, 2003). In general, to maximise stiffness (and thermal properties) it is necessary to achieve fiiU exfoliation and dispersion which is not readily achieved (Vu etal., 2001, Zhang etal., 2004). 

T.J. Pinnavaia, T. Lan, Z. Wang, H. Shi and P.D. Kaviratna, Clay-reinforced epoxy nanocomposites Synthesis, properties, and mechanism of formation. In G.-M. Chow and K.E. Gonsalves (Eds.), Nanotechnology Molecularly Designed Mlaterials, American Chemical Society, Washington, 1996, Vol. 622, p. 250. 

To clarify the mechanisms of the clay-reinforced carbonaceous char formation, which may be responsible for the reduced mass loss rates, and hence the lower flammability of the polymer matrices, a number of thermo-physical characteristics of the PE/MMT nanocomposites have been measured in comparison with those of the pristine PE (which, by itself is not a char former) in both inert and oxidizing atmospheres. The evolution of the thermal and thermal-oxidative degradation processes in these systems was followed dynamically with the aid of TGA and FTIR methods. Proper attention was paid also to the effect of oxygen on the thermal-oxidative stability of PE nanocomposites in their solid state, in both the absence as well as in the presence of an antioxidant. Several sets of experimentally acquired TGA data have provided a basis for accomplishing thorough model-based kinetic analyses of thermal and thermal-oxidative degradation of both pristine PE and PE/MMT nanocomposites prepared in this work. 

Yua Yuan, Q., Misra, R. D. K. Impact fracture behaviour of clay-reinforced polypropylene nanocomposites. Polymer Vol. 47 (2006) 4421-4433. 

Lan T, WangZ, Shi H, PinnavaiaTJ (1995) Clay-epoxy nanocomposites relationships between reinforcement properties and the extend of clay layer exfoliation, in Polimeric Materials - Science and Engineering. Proceedings of the ACS Division of... 

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. 

In this chapter, the methods of producing clay-polymer nanocomposites are discussed in detail. The influence of clay reinforcement on the mechanical, thermal and physical properties of thermoplastic and thermosetting polymers is also discussed. This chapter also comprises of processing techniques of polymer nanocomposites using nanoparticles hke Al O, CaCO, TiO, ZnO and SiO as reinforcements. These materials have the potential to alter tribological, electrical and optical properties considerably. 

Clay-polymer nanocomposites, a new class of hybrids, came into the purview of researchers after their invention by the Toyota research group [7,8]. They found dramatic improvement in tensile properties of polymers by adding clay in small weight fractions. In continuation of this, other researchers have used various techniques to develop polymer nanocomposites with clay as reinforcement after proper organic treatment. 

Figure 9.12 Differential scanning calorimetry plots for neat PP and 4 wt% clay-reinforced PP nanocomposite. Reprinted from [58] with permission from Elsevier.

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]. 

The flammability behaviour of clay-polymer nanocomposites could be restricted by incorporating the nano-clay as reinforcement in limited volume fraction. The heat release rates also are found to be diminished substantially by nano-clay incorporation. The flammability resistance can be enhanced by the incorporation of nano-clay platelets without compromising other properties [114]. This improvement in flammability resulted in development of Wire Cable jacket material [115]. 

Lan, T. and Pinnavaia, T. J. 1994. Clay-reinforced epoxy nanocomposites. Chemistry cf Materials 6 2216-2219. 

The achievement of a high degree of exfoliation of layered clay minerals in nonpolar rubber matrices, such as NR, is still a major issue. This chapter presents a brief overview of studies of clay reinforcement in NR both in micro and nano scale. Although quite a lot of studies have been reported in the field of NR reinforcement with simple organoclay (OMt), plenty of scope still exists to improve the dispersion of MMT followed by property enhancement. Better dispersion and improvement in dilferent properties was observed in the case of EOMt-filled NR nanocomposites. 

A pronounced difference in stress-strain behaviour and SIC of various clay-reinforced NR nanocomposites are shown in Figure 22.9. 

Pinnavaia, T. J. Lan, T. Wang, Z. Shi, H. Kaviratna, P. D., Clay-Reinforced Epoxy Nanocomposites Synthesis, Properties, and Mechanism of Formation. 

Chen F, Lou D, Yang J, Zhong M (2011) Mechanical and thermal properties of attapulgite clay reinforced polymethylmethacrylate nanocomposites. Polym Adv Technol 22 1912-1918... 

Xu B, Huang WM, Pei YT, Chen ZG, Kraft A, Reuben R, De Hosson JTM, Fu YQ (2009) Mechanical properties of attapulgite clay reinforced polyurethane shape-memory nanocomposites. Eur Polym J 45 1904-1911... 

Ali ES, Zubir SA, Ahmad S (2012) Clay reinforced hyperbranched polyurethane nanocomposites based on pahn oil polyol as shape memory materials. Adv Mater Res 548 115-118... 

Clay-Reinforced Epo] Nanocomposites Synthesis, Properties, and Mechanism of Formation... 

Relative modulus versus talc clay-reinforced agent content for nanocomposites based on a thermoplastic polyolefin or a triphenylene oxide matrix polypropylene plus ethylene-based elastomer showed that relative to a particular filler content, an appreciably higher modulus content was obtained for the montmorillonite reinforcing agent than for talc [156]. Doubling the modulus of the phenylene oxide requires about four times more talc than montmorillonite, with the talc-reinforced polymer having an improved surface finish. In the case of the talc-reinforced polymer, exfoliation is appreciably better than with clay reinforcement. The talc-reinforced polymer has automotive applications. 

In some polymer nanocomposites the initial thermal decomposition will be accelerated due to the presence of alkyl ammonium surfactant on the surface of the clay. For instance in PVC the quaternary ammonium salts may accelerate the degradation of PVC.However, this problem does not exist in clay reinforced natural rubber nanocomposites. 

Some important nanostructures include carbon nanotubes, montmorillonite type clays, and biomolecules such as proteins and DNA. Frequently, these nanomaterials self-assemble into highly ordered layers or structures arising from hydrogen bonding, dipolar forces, hydrophilic or hydrophobic interactions, etc. For maximum reinforcement, however, proper dispersal of these nanostructures has become a major research effort. The following sections will emphasize the structure and behavior of carbon nanotube and montmorillonite clay based nanocomposites. 

Lan Tie, and Pinnavaia J. Thomas. Clay-reinforced epoxy nanocomposites. J. Chem. Mater. 6 no. 12 (1994) 2216-2219. 

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