**2.2 Melt blending**

The melt blending need heat and high shear pressure to disperse the nanoparticles in polymer matrix and it is well-matched with present industries. In comparison with solution blending, the melt mixing has less effective at dispersion of nanoparticles in polymer matrix and has limitation for low concentration of nanoparticle because of high viscosities of the composites at higher nanoparticles loadings.

Melt mixing of nanoparticles into thermoplastic polymer matrix using conventional processing techniques, such as extrusion, injection molding, and blow molding are particularly desirable, due to the speed, simplicity, and availability of the process in plastic industries. These methods are also benefit due to free of solvent and related contaminant. The nanoparticles has a unique advantage in thermoplastic polymer compounding and molding, because less fiber cutting or breaking occurs, and a high aspect ratio is maintained for one dimensional fillers in contrast to larger, microscale fillers. Application of shear mixing with long processing time may improve the dispersion of fillers, and when coupled with elongating extrusion, should yield adequate aligned nanofillers. Increasing in viscosity is higher for nanofibers than that of large diameter fibers such as carbon black, so shear mixing is necessary to overcome the high viscose polymer/nanofibers composites. Additionally, another advantage is the vision of recycling thermoplastic nanocomposites to decrease the financial expenses and to become safe for environment. Nevertheless, much needs to be learned about the ability of nanofibers to withstand high shear and elongation flow processing and about optimization of processing parameters to provide good nanofibers dispersion.

Controlling the alignment of nanofibers in polymer matrix is possible using melt mixing methods. For example, spinning of extruded melt samples is used for alignment of fillers in nanofibers/polypropylene nanocomposites with high dispersion of nanofibers. Up to now, various methods of nanofiber alignment techniques have been developed such as using further increment in residence time in the die channel or die design to control the orientation of nanofibers. Injection molding was also found to induce significant alignment in nanofibers/ polypropylene composites, as demonstrated by measurement of thermal expansion and electrical conductivity.

#### **2.3 In situ polymerization**

The nanoparticles are dispersed in monomer and then the polymerization process is starts. As solution blends, functionalized nanoparticles can improve the initial dispersion of the nanoparticles in the liquid (monomer and solvent) and consequently in the nanocomposites. Furthermore, in situ polymerization methods enable covalent bonding between nanoparticles and the polymer matrix using various condensation reactions. Noteworthy extensions of in situ polymerization include infiltration methods in which the reactive agents are introduced into a nanoparticle structure and subsequently polymerized.
