**1. Introduction**

Recent technological advances and the need for materials with new functionalities and bet‐ ter performance have generated an enormous demand for novel materials. Nanostructures such as carbon nanotubes (CNTs) possess outstanding mechanical, electrical, thermal and chemical properties which make them ideal for a wide variety of current or future applica‐ tions [1], especially for the preparation of multifunctional *hybrid polymer materials*.

The incorporation of CNTs to polymer matrices have demonstrated to improve the mechani‐ cal, electrical, thermal and morphological properties of the produced nanocomposites [2]; however, the full exploitation of CNTs has been severely limited due to difficulties associat‐ ed with dispersion of entangled CNTs during processing, and their poor interfacial interac‐ tion with the polymer matrix. Therefore, significant efforts have been directed toward improving the dispersion of CNTs by means of surface modification either by non-covalent functionalization or covalent functionalization [3].

Most strategies designed to functionalize CNTs involve the use of strong acids as reagents and organic solvents as reaction media, which can become environmental pollution and health hazard problems. Nowadays, the global environmental trends are seeking greener chemistry methods to prepare materials, thus, there is plenty of room for developing envi‐ ronmentally-friendly chemistry methods to functionalize CNTs.

© 2013 Ávila-Orta et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Ávila-Orta et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

"*Green*" chemistry is based on the use of a set of principles that reduces or eliminates the use of hazardous reagents and solvents in the design, preparation and application of materials [4]. In this context, functionalization of CNTs using microwaves, plasma, and ultrasound waves are strategies very promising for greener production of hybrid polymer materials, due to shorter reaction times, reduced energy consumption, and better yields.

a hybrid polymer material play a key role in determining its properties. Figure 1 shows a scheme of hybrids materials composed by two components, in which one of them is ar‐

Toward Greener Chemistry Methods for Preparation of Hybrid Polymer Materials Based on Carbon Nanotubes

http://dx.doi.org/10.5772/51257

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The hybrid polymer materials can be classified depending of the nature of interactions be‐ tween their components. In particular, when structural materials in the form of particles, flakes or fibers are incorporated into polymer matrices, this type of hybrid polymer materi‐ als can be classified in (i) *class I* hybrid materials, which show weak interactions between the two components, such as van der Waals, hydrogen bonding or weak electrostatic interac‐ tions, and (ii) *class II* hybrid materials, which show covalent interactions between both com‐ ponents such that there is no tendency for the components to separate at their interfaces

Hybrid polymer materials containing CNTs have attracted considerable attention due to the unique atomic structure, high surface area-to-volume ratio and excellent electronic, mechanical and thermal properties of carbon nanotubes. Although the incorporation of CNTs to polymer matrices have significantly improved the mechanical, electrical and morphological properties of polymers, there is plenty of room for controlling the structur‐ al configuration of the hybrid polymer material, thus, different efforts have been focused

Since the first ever materials based on polymer-CNTs were reported in 1994 by Ajayan *et al*. [7], several processing methods have been developed for fabricating polymer-CNTs hy‐ brid materials. These methods mainly include solution mixing, *in-situ* polymerization, and

Because the unique mechanical properties of CNTs, such as the high modulus, tensile strength and strain to fracture, there have been numerous efforts to obtain hybrid materials with im‐ proved mechanical properties [2]. Within the structural configurations for this specific applica‐ tion, the "*chopped fibers*" configuration, as seen in Figure 1(d), has been the most desired.

On the other hand, for other unique properties of CNTs such as high electrical and thermal conductivity, the obtaining of multiphase polymer amorphous blends, as seen in Figure 1(f), offers a much higher potential for the development of conductive composites containing CNTs. The selective localization of the CNTs either in one of the blend phases or at the inter‐ face of an immiscible co-continuous blend can form an ordered network of conductive phase, creating the so-called segregated systems [9]. In such systems, considerably lower value of per‐ colation threshold compared to "*chopped fibers*" structural configuration can be achieved.

The building of polymer-CNTs hybrid materials with desired structural configurations is po‐ tentially promising to develop advanced hybrid materials; however, the full exploitation of

ranged so that synergistic properties can be achieved.

when the hybrid material is loaded [6].

**3. Polymer-CNTs hybrid materials**

in the preparation methods.

**3.1. Structural configuration**

melt blending [8].

The focus of this chapter will be on the microwaves, ultrasound and plasma assisted func‐ tionalization of CNTs as greener chemistry methods to produce hybrid polymer materials. After a brief overview on preparation of hybrid polymer materials containing CNTs, we will present the physical principles, mechanisms and processing conditions involved in the func‐ tionalization of CNTs for each of these "*Green*" chemistry methods, and then present our point of view on challenges and opportunities in both the immediate and long-term future.
