Applied Sciences  
Application of Quaternary Ammonium Compounds as Compatibilizers for Polymer Blends and Polymer Composites--A Concise Review  
[PERSON] 1,*(c) and [PERSON] 2,3,*(c)  
1 Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, University Putra Malaysia, Serdang 43400, Selangor, Malaysia 12 Department of Chemistry, Faculty of Science, University Putra Malaysia, Serdang 43400, Selangor, Malaysia 23 Centre of Foundation Studies for Agricultural Science, University Putra Malaysia, Serdang 43400, Selangor, Malaysia 34  
In general, polymer blends are combinations of two or more polymers, whereas polymer composites are compound made up of polymer matrix and filler components. The preparation of polymer blends and polymer composites is typically intended to obtain materials that have a combination of excellent properties of the different materials. This approach is commonly inexpensive and less time-consuming than the development of new polymeric materials. They are classified as compatible and incompatible materials. Compatible polymer blends and polymer composites have superior thermo-mechanical properties (e.g., degradation temperature, glass transition temperature, melting temperature, tensile strength, flexural strength, impact strength, etc.), while incompatible matters commonly have poor thermo-mechanical properties. The compatibilization is usually done on the incompatible polymer blends and polymer composites because they have a difference in polarity that affected their thermo-mechanical properties. Moreover, the use of compatibilizers in polymer blends and polymer composites is to improve their interfacial adhesion [5; 6] by creating the intermolecular interactions between the blend and composite components [7; 8]. Table 1 shows the examples of polymer blends compatibilized by QACs.  
Table 2 indicates the examples of polymer composites compatibilized by QACs. The selection of the polymer blends and polymer composites in this concise review is not randomly based on the materials compatibilized by QACs, but it is based on the thermo-mechanical properties that were comprehensively studied in the previous research works.  
In the past ten years, many compatibilization approaches have been recommended for the intention of enhancing the thermo-mechanical properties of polymer blends and polymer composites. The application of QACs as compatibilizers could provide an advantage because of their unique chemical structure that owns both polar ionic and non-polar lipophilic functional groups [26]. These groups are able to interact with polar hydrophilic and non-polar hydrophobic polymers or materials. The intermolecular interactions could contribute to the compatibilization effect on polymer blends and polymer composites, and consequently improve the interfacial adhesion between their components. Yet, to the authors' knowledge, there is no concise review prepared concentrating on the application of QACs as compatibilizers for polymer blends and polymer composites. That is the objective of making a categorized review in this paper, which consists of related research works.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Polymer Blend** & **Abbreviation** & **References** \\ \hline Nylon-6/liquid natural rubber & Nylon-6/LNR & [9] \\ Natural wool/cellulose & NW/Cellulose & [10] \\ Polyethylene terephthalate/polyethylene & PET/PE & [11] \\ Polybutylene succinate/rice starch & PBS/RS & [12] \\ Poly(ethylene oxide)/chitosan & PEO/Chitosan & [13] \\ Agar/rice starch & Agar/RS & [14] \\ Poly(3-hydroxybutyrate-co-3- & PHBW/Cellulose & [15] \\ hydroxyvalerate)/cellulose & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Examples of polymer blends compatibilized by quaternary ammonium compounds (QACs).  
Figure 1: Schematic of the quaternization of \(N\)-methyldiethanolamine with benzyl chloride to produce benzylbis(2-hydroxyethyl)methylammonium chloride.