## 2 Polymer Blend and Polymer Composite Materials  
### Polymer Blend Materials  
The polymer blend materials can be prepared either in the melt, solution, or emulsion condition. The blending process involves at least two different polymers. The melt blending process must be carried out at elevated temperatures, precisely at the fusing temperature of the polymer components [27]. The solution blending process can be conducted in appropriate solvents that are capable to dissolve polymers completely [14]. The emulsion blending process involves dispersion of emulsion of at least two different polymers [28]. The compatible polymer blends have remarkable thermo-mechanical properties based on the complementary behavior of their individual components [29]. The preparation of polymer blend materials is straightforward when conventional blending machines are used [30].  
The polymer blends can be made either from synthetic thermoplastic polymers or from natural biodegradable polymers by blending between the synthetic/synthetic polymers, natural/natural polymers, or synthetic/natural polymers. Table 3 shows the examples of polymer blends, blend types, blending conditions, and blending machines. Synthetic thermoplastic polymer blends can be prepared via melt, solution and emulsion blending processes [31]. The chemical structure of the main chains of thermoplastic polymers has allowed them to be processed in such conditions, including the nature of the intermolecular interaction of the polymers. Nevertheless, for natural biodegradable polymer (biopolymer) blends, they are usually prepared through solution blending process; this is because most of them do not melt but decompose at elevated temperatures [14]. The chemical nature of biopolymers has also allowed them to be processed in such condition because they were bonded with hydrogen bonding. Figure 2 exhibits the chemical structures of PET, PBS, PEO, and PHBV. The melt blending process can be done by using compounder or extruder. In contrast, solution and emulsion blending processes can be performed by means of mechanical stirrer, magnetic stirrer, or KPG stirrer.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Polymer Composite** & **Abbreviation** & **References** \\ \hline High-/low-density polyethylene/cellulose & HDPE/LDPE/Cellulose & [16] \\ Carboxylated styrene butadiene rubber/rice bran carbon & XSBR/RBC & [17] \\ Poly(Bisphenol-A-co-epichlorohydrin)/boron nitride & PBE/BN & [18] \\ Agarose/Tc & [19] \\ Styrene-butadiene rubber/bentonite & SBR/Bentonite & [20] \\ Diglycidyl ether of bisphenol A epoxy/chitin & DGEBA epoxy/Chitin & [21] \\ High-density polyethylene/agar & HDPE/Agar & [22] \\ Polyurethane/silica & PU/SiO & [23] \\ Nylon-6/LNR/montmorillonite & Nylon-6/LNR/MMT & [24] \\ Regenerated cellulose/montmorillonite & RC/MMT & [25] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Examples of polymer composites compatibilized by quaternary ammonium compounds (QACs).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Polymer Blend** & **Blend Type** & **Blending Condition** & **Blending Machine** & **References** \\ \hline PET/PE & Synthetic/synthetic & Melt & Twin-screw compounder & [11] \\ Agar/RS & Natural/natural & Solution & Magnetic stirrer & [14] \\ Chitin/Cellulose & Natural/natural & Solution & KPG stirrer & [32] \\ PBS/RS & Synthetic/natural & Melt & Twin-screw extruder & [12] \\ PEO/Chitosan & Synthetic/natural & Solution & Mechanical stirrer & [13] \\ PHBV/Cellulose & Synthetic/natural & Solution & Magnetic stirrer & [15] \\ Nylon-6/LNR & Synthetic/natural & Emulsion & Mechanical stirrer & [9] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Examples of polymer blends, blend types, blending conditions, and blending machines.