Methods of Nanocomposite Preparation

The method of nanocomposite preparation has a great influence on the properties of the resulting composite. The methods mainly used are solution blending, melt blending, and in situ polymerization. 

Thus, melt blending method of nanocomposites preparation is a common alternative, and is particularly useful for thermoplastics processing. This method is based on high temperatures and shear to disperse nanoparticles on the polymer matrix, and has advantages as its speed and simplicity, besides being the most compatible with currently industrial processes, among which, extrasion is the most practiced (Coleman et al. 2006a, b Esawi et al. 2010 Lee et al. 2005 Moniruzzaman and Winey 2006). 

Ray et al. [93] treated organically modified MMT (OMMT) with a MAO solution after vacuum-drying at 100°C. The resulting MAO-treated clay was subsequently used for ethylene polymerization in the presence of 2,6-bis [l-(2,6-diisopropylphenylimino)ethyl]pyridine iron(ll) dichloride with additional MAO in a glass reactor. In addition, they compared the methods of nanocomposite preparation and observed that the nanocomposite produced by catalyst supported on MAO-pretreated OMMT was more efficiently exfoliated than the nanocomposite produced when only a mixture of catalyst and clay was used. This result led them to conclude that at least some of the active centers resided within the clay galleries. Similarly, Guo et al. [100] in a separate studies successfully used pyridine diimine-based iron(ll) catalysts for preparation of exfoliated PE/clay nanocomposites. 

The principle a and a concrete scheme b of nanocomposite preparation by such a method is shown in Fig. 8-7. 

This chapter has analyzed the principal methods, structural organization and architecture of a wide range of metallopolymers obtained by incorporation of metal particles into polymers, as well as promising new ones. The multiplicity of architectural structures in such self-organized systems is a reflection of the infinite variety of natural objects coupled with the synthetic possibilities of chemistry. Even the term supramolecular architecture has appeared [104]. Almost all architectural forms (including those obtained by sol-gel methods in thin-layered films) are used in nature for generation of metal particles in biopolymers and their analogues. Primarily, this relates to supramolecular polyfunctional systems such as enzymes, liposomes and cells. The processes of nanocomposite preparation are very similar to biomineralization, biosorption etc. 

Carbon-based polymer nano composites represent an interesting type of advanced materials with structural characteristics that allow them to be applied in a variety of fields. Functionalization of carbon nanomaterials provides homogeneous dispersion and strong interfacial interaction when they are incorporated into polymer matrices. These features confer superior properties to the polymer nanocomposites. This chapter focuses on nanodiamonds, carbon nanotubes and graphene due to their importance as reinforcement fillers in polymer nanocomposites. The most common methods of synthesis and functionalization of these carbon nanomaterials are explained and different techniques of nanocomposite preparation are briefly described. The performance achieved in polymers by the introduction of carbon nanofillers in the mechanical and tribological properties is highlighted, and the hardness and scratching behavior of the nanocomposites are also discussed. 

Hiroi et al. [15] prepared PLA/organically modified layered titanate (OHTO) nanocomposites by a melt extrusion method. For nanocomposite preparation, the OHTO (dried at 120°C for 8h) and PLA were first dry mixed by shaking them in a bag. The mixture was then melt extruded using a twin-screw extruder (KZW15-30TGN, Technovel Corp.) operated at 195°C (screw speed = 300 rpm, feed rate = 22 g/ min) to yield nanocomposite strands. XRD patterns and TEM observations showed the formation of intercalated structures. 

First and paramount method of nanocomposites characterization is, undoubtedly, transmission dectron microscopy (TEM), which allows one to observe the particle shape, to determine particle sizes, to control the homogeneity of the composite and to obtain the histogram of nanoparticle sizes (Figs. 1, 2). TEM (especially axial bright fidd microscopy) is the most informative method of characterization with the resolution up to units of angstroms allowing visualization of the lattice plane and measurement of interplanar distances of nano-partides. However, its application to polymer composites is hindered due to charge instability of some polymers (such as PVA [39], or PVDF [35]) and by the difficulty of sample preparation. 

In situ polymerization is a method of bionanocomposite preparation whereby the nanostructured reinforcement, usually layered clays, is dispersed in a liquid monomer or a monomer dissolved in a suitable solvent for a certain amount of time, allowing monomer molecules to diffuse between the layers. Upon further addition of initiator or exposure of appropriate source of light or heat, the polymerization takes place in situ forming the nanocomposite. 

A variety of more complicated compounds having a CH2CH2 linkage to the POSS core have been prepared using methods outlined in Table 29. Thus, epoxides have been made from cyclohexene-terminated POSS (Table 29, entries 1 and 2) and are precursors for the preparation of nanocomposite polymers under ultraviolet irradiation (Figure 43). ... 

Depending on the namre of filler, type of dispersion, and method of preparation, the nanocomposites can be divided into subclasses. 

ENGAGE is an ethylene-octene copolymer. Ray and Bhowmick [70] have prepared nanocomposites based on this copolymer. In this study, the nanoclay was modified in situ by polymerization of acrylate monomer inside the gallery gap of nanoclay. ENGAGE was then intercalated inside the increased gallery gap of the modified nanoclay. The nanocomposites prepared by this method have improved mechanical properties compared to that of the conventional counterparts. Preparation and properties of organically modified nanoclay and its nanocomposites with ethylene-octene copolymer were reported by Maiti et al. [71]. Excellent improvement in mechanical properties and storage modulus was noticed by the workers. The results were explained with the help of morphology, dispersion of the nanofiller, and its interaction with the mbber. 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

Outside of catalyst preparation, reaction of sucrose with metal nitrates has been used to prepare nanocomposite mixed oxide materials. Wu et al. [46] reported the synthesis of Mg0-Al203 and Y203-Zr02 mixed oxides by reaction of nitrate precursors with sucrose. The resulting powders had smaller particles than those prepared without sucrose. Das [47] used a similar method in the presence of poly vinylalcohol to produce nanocrystalline lead zirconium titanate and metal ferrierites (MFe204, M = Co, Ni, or Zn). The materials prepared using sucrose had smaller crystallites than those made without. Both authors observed an exothermic decomposition of the precursors during calcination. 

---