# A Review of the Synthesis and Applications of Polymer-Nanoclay Composites
## 2 Synthesis
### Solution-Blending Method  
Solution-blending is a solvent based process in which the polymer and the prepolymer are soluble, which causes swelling of the clay layers, see Figure 2[51]. The layered clay is exfoliated onto single layers using a solvent in which the polymer or prepolymer is soluble, such as water, chloroform, or toluene [52]. When the polymer/prepolymer and layered clay are mixed in a solution, the polymer chains intercalate and displace the solvent within the interlayer of the clay [53]. Upon solvent removal (by vaporization or precipitation), the intercalated sheets reassemble, resulting in polymer/nanoclay composites [53]. The driving force of intercalation in solution blending is the entropy gained from desorption of solvent molecules [54]. The entire process typically consists of three stages, namely the dispersion of clay in a polymer solution, controlled removal of the solvent, and finally, composite film casting [53]. The dispersion of clay requires energetic agitation such as stirring, reflux and shear mixing. Recently, ultrasonication has become an efficient approach to improve the dispersion of nanoclays in a polymer solution, by breaking up nanoclay clusters through cavitation in the solution and/or exciting resonance vibrations of the clusters. Nanoclay contents, sonication type (bath or tip), solvent type, and sonication time impact the quality of the dispersion of nanoclays in the polymer solution [52]. Ultrasonication is applicable for processing both thermoplastic and thermoset polymers [55]. For instance, [PERSON] et al. [37] modified Algerian clay using ultrasonication and synthesized poly-glycidyl methacrylate (GMA)/nanoclay composites. The results confirmed the intercalation of surfactants within the clay layers and the composites exhibited significant improvement in their thermal stabilities compared to unmodified poly-GMA. Ultrasonication appears to offer several advantages in terms of reaction time, clay dispersion and polymer/nanoclay composite yield [56]. [PERSON] et al. [57] synthesized a halloysite nanoclay-based poly(methyl methacrylate) (PMMA) and polystyrene (PS) composite using an ultrasound-assisted, solution blending method. Various glass surfaces were coated with the synthesized composites, which resulted in the improved scratch resistance and hydrophobicity of the surfaces. The enhanced thermal and mechanical properties of these composites were attributed to the highly dispersed nature of halloysite nanoclay fillers. Removal of the solvent also plays a critical role in the physical properties of the polymer/nanoclay composites; slow evaporation of the solvent may yield a composite with a high polymer crystallinity [56]. The solution blending method is usually used to prepare thermoplastic and thermoset composites (epoxy composites) at the laboratory scale due to its easy operation, excellent particle dispersion, and coupling chemical reactions [55]. Meanwhile, several studies, such as that by [PERSON] et al. [58] have shown the possibility of preparing intercalated or exfoliated rubber composites. In their study, rubber/MMT composites were prepared using solution blending and the structure and properties of the prepared composites were compared with composites produced via melt blending. The results indicated that solution blending delivers a similar composite structure, yields a higher amount of bound rubber, and enhances the compression set, hardness and dynamic mechanical properties. [PERSON] et al. [59] synthesized exfoliated ethylene-octene copolymer/MMT composites using a solution blending technique, which improved the tensile modulus by 63%, tensile strength by 44%, storage modulus by 14% and resulted in a 10 \({}^{\circ}\)C shift in glass transition temperature compared to the neat copolymer. [PERSON] et al. [60] utilized a highly volatile organic separator solvent to generate PS/MMT composites at melt compounding temperatures (transfer batch blending).