## 5 General Discussion  
Taking into account the thermophysical characterization from the cycling stability tests results, only dimethyl terephthalate, benzanilide, potassium thiocyanate, HDPE, benzamide, phtalic anhydride, and adipic acid showed a suitable stability after 100 cycles. However, benzamide and benzanilide presented remarkable differences between solidification and melting temperatures at the laboratory scale. Therefore, these two candidates might be interesting to be tested at a higher scale to study this phenomenon since the differences between solidification and melting temperatures and subcooling of PCM are mass dependent [17]. From this first filter, and taking into account the chemical characterization, it was seen that adipic acid showed the same chemical spectrum after cycling tests, while HDPE, potassium thiocyanate, and dimethyl terephthalate did not exhibit important chemical degradation but rather the appearance or disappearance of some peaks. Moreover, from the health hazard point of view, potassium thiocyanate should be disregarded due to its high hazard value according to the methodology explained. Adipic acid and dimethyl terephthalate present a low health hazard value, whereas HDPE appears to be hazardous, being easy to handle and not presenting any hazardous GHS statement. Finally, bearing in mind the thermal stability tests, only HDPE and adipic acid would be suitable PCMs for thermal processes working under partial load operating conditions in the temperature range between 120 and 200 \({}^{\circ}\)C.  
A summary of the results of the deep experimental characterization of the sixteen PCM in the temperature range between 120 and 200 \({}^{\circ}\)C is provided in Table 5.  
Figure 3: FT-IR spectroscopy results: (**a**) Adipic acid; (**b**) Benzanilide; (**c**) HDPE; (**d**) Dimethyl terephthalate; (**e**) Dulcitol; (**f**) Urea.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Material**} & \multirow{3}{*}{\begin{tabular}{c} **Health** \\ **Hazard** \\ \end{tabular} } & \multicolumn{3}{c}{\begin{tabular}{c} **Cycling Stability** \\ **(after 100 Cycles)** \\ \end{tabular} } & \multicolumn{3}{c}{\begin{tabular}{c} **Thermal** \\ **Stability** \\ \end{tabular} } \\  & & \multicolumn{1}{c}{**Phase Change**} & \multicolumn{1}{c}{**Chemical**} & \multicolumn{1}{c}{\
\begin{tabular}{c} **Maximum** \\ **Thermal-Stable** \\ **Temperature** \\ \end{tabular} } \\  & & \multicolumn{1}{c}{**Enthalpy Loss (\%)**} & \multicolumn{1}{c}{**Depgradation** \({}^{\circ}\)**} & \multicolumn{1}{c}{
\begin{tabular}{c} **Thermal** \\ **Stability** \\ \end{tabular} } \\ \hline Benzoic acid & 2 & 100 & ++ & 121 & No \\ Benzamide & 2 & 14 & ++ & 138 & No \\ High density & 0 & 12 & + & 309 & Yes \\ polyethylene (HDPE) & & & & & \\ Sebacic acid & 1 & 63 & ++ & 118 & No \\ Phtalic anhydride & 3 & 6 & + & 129 & No \\ Maleic acid & 3 & ** & ++ & 141 & No \\ Urea & 2 & ** & ++ & 148 & No \\ Dimethyl terephthalate & 1 & 2 & + & 128 & No \\ D-mannitol & 1 & 61 & ++ & 259 & No \\ Adipic acid & 1 & 7 & - & 203 & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 5: Summary of the characterization of the sixteen PCMs under study.