## 4 Microencapsulation Techniques
### Physical Process
#### 4.2.1 Spray Drying  
Spray drying consists of dispersing PCMs in an aqueous coating medium into a heated chamber where solvent evaporation takes place to rigidify the microcapsules shell. Firstly, the emulsion is sprayed in tiny droplets with an atomizer. Then, sprayed droplets are carried by the gas stream at an adequate temperature for the solvent's complete evaporation. Finally, solid particles treated by the gas phase are collected using a cyclone, filter bag, or electrostatic precipitator [37].  
The benefits of this process are its low cost, high yield production, and partial versatility [137]. Meanwhile, the main drawbacks are particles aggregation and the use of high temperature [138]. [PERSON] et al. encapsulated paraffin Rubitherm(r)RT27 using polyethylene-ethyl vinyl acetate (LDPE-EVA) as a copolymer [139]. They obtained homogeneous microcapsules with small particle sizes and high microencapsulation efficiency. The shape of microcapsules collected from the collection vessel was more defined and homogeneous than those collected into the drying chamber (Figure 8). Nevertheless, one of the main drawbacks of this process is the aggregation taking place in the drying chamber, which can be minimized by controlling the temperature or using a high stream of the gas carrier.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Method** & **Shell** & **Core** & \(\mathbf{T_{m}}\)**mPCMs (\({}^{\circ}\)C)** & **LC (\%)** & \(\mathbf{\Delta H_{f}(J\cdot g^{-1})}\) & **Size (\(\upmu\)m)** & **Ref.** \\ \hline MUF & \(n\)-Dodecanol & 21 & 91 & 131 & 38 & [113] \\ \hline MF/MMF & \(n\)-Dodecanol & 28 & 50–83 & 110–181 & 0.71–6.28 & [114] \\ \hline MMF/BMF & \(n\)-Dodecanol & 24 & 50 & 100 & 2–5 & [115] \\ \hline CNFs/MF & 1-Dodecanol & 26 & 50 & 100 & 1–3 & [119] \\ \hline PNDA/MF & \(n\)-Dodecanol & 32 & - & 110–141 & 0.08–0.14 & [136] \\ \hline Polyurea & \(n\)-Octadecane & - & 70 & - & 7.3 & [122] \\ \hline Polyurea/polyurethane & \(n\)-Octadecane & 29 & - & 143 & 3–5 & [126] \\ \hline Polyurea/polyurethane & \begin{tabular}{c} Butyl stearate \\ paraffin \\ \end{tabular} & 28–35 & 40–60 & 58–87 & 5–15 & [129] \\ \hline Polyurethane & Butyl stearate & 22 & - & 80 & 10–35 & [130] \\ \hline Polyurea & \begin{tabular}{c} Ethyl \\ palmitate \\ \end{tabular} & 19 & 62 & 123 & 10 & [131] \\ \hline Interfacial polycondensation & \begin{tabular}{c} Ethyl \\ palmitate \\ \end{tabular} & 17 & 55 & 110 & 10 & [131] \\ \hline SiO\({}_{2}\)/polyurea & \begin{tabular}{c} Ethyl \\ palmitate \\ \end{tabular} & 22 & 59 & 120 & 10 & [131] \\ \hline SiO\({}_{2}\)/polyurethane & \
\begin{tabular}{c} Ethyl \\ palmitate \\ \end{tabular} & 17 & 61 & 122 & 10 & [131] \\ \hline Polyurethane &
\begin{tabular}{c} Dodecanol \\ dodecanoate \\ \end{tabular} & 32 & 54–74 & 103–140 & 10–40 & [132] \\ \hline c-PU & Butyl stearate & 24 & - & 106 & 4.46 & [133] \\ \hline \hline \end{tabular}
\end{table}
Table 3: _Cont._[PERSON] et al. employed a spray-drying method to prepare polylactic acid (PLA)/sodium monofluuorphosphate microcapsules [140]. They obtained porous microcapsules with lower encapsulation efficiency due to the low viscosity of PLA. The spray pressure regulation influenced the particles size.