## 3 Results and Discussion
### Characterization of RT18 HC@AC Filler
#### 3.1.2. Thermal Properties of AC-RT18 HC Filler  
A thermogravimetric analysis (TGA) was employed to study the thermal degradation characteristics of the RT18 HC@AC composites, with different RT18 HC loadings, as well as to estimate the real mass of RT18 HC encapsulation into the activated carbon matrix. Figure 3 presents the TG% curves of the composite materials in comparison with pure RT18 HC. The TG% curve of pure RT18 HC reveals one thermal degradation stage at the range of \(\sim\)130-230 \({}^{\circ}\)C, which is accompanied with a 95% weight loss due to the volatilizations of paraffin. In the case of the RT18 HC@AC composites, a noteworthy trend emerged as a function of RT18 HC loading, wherein an increase in the RT18 HC content was correlated with a higher mass loss from 19.93% for a 10% loading to 54.73% for 300% loading. Also, RT18 HC thermal degradation occurred at two stages, one at a temperature up to 230 \({}^{\circ}\)C, and a second one at higher temperatures up to 460 \({}^{\circ}\)C. The initial weight loss, which is observed at lower temperatures, probably corresponds to the thermal degradation of RT18 HC, which is adsorbed on the outer surface of activated carbon (macropores), whereas the second weight loss at higher temperatures is attributed to same degradation of the RT18 HC molecules that are adsorbed on the smaller meso- and micropores where more energy is needed for their degradation. Table 3 summarizes RT18 HC loading on AC according to weighting  
Figure 1: Leaching tests at 30 \({}^{\circ}\)C for 8 h of the produced hybrid AC-RT18 HC samples with (**a**) 20%, (**b**) 50%, (**c**) 80%, (**d**) 100%, (**e**) 200%, and (**f**) 300% RTHC18. and thermogravimetric results. The 3 RT18 HC@AC material was selected as the additive for the composite gypsum boards since it exhibits the higher PCM loading (54.73%), and no leaching of the PCM phase was observed during the leaching tests. Although none of the xRT18 HC@AC materials showed leaching of the PCM component, the materials with the highest PCM loadings on AC are preferable since they will offer more encapsulated effective materials on the gypsum board, leading to better thermal storage properties. Figure 3: Thermogravimetric analysis (TG%) curves of AC-RT18 HC hybrids with different RTHC18 loading during the synthesis. Figure 2: Leading tests at 80 \({}^{\circ}\)C for 72 h of the produced hybrid AC-RT18 HC samples with (**a**) 20%, (**b**) 50%, (**c**) 80%, (**d**) 100%, (**e**) 200%, and (**f**) 300% RTHC18. Figure 4 shows the DSC curves of the 3 RT18 HC@AC composite in comparison with the corresponding curves of pure RT18 HC. Also, the melting and freezing temperatures (T\({}_{\text{m}}\) and T\({}_{\text{s}}\)) as well as the corresponding enthalpies (\(\Delta\)H\({}_{\text{m}}\) and \(\Delta\)H\({}_{\text{s}}\)) are shown in this figure. The melting point of pure RT18 HC at 19.6 \({}^{\circ}\)C and its freezing point at 8.2 \({}^{\circ}\)C align with its known phase change characteristics. The observed asymmetry in the exothermic and endothermic peaks suggests the presence of multiple crystalline phases within RT18 HC. According to the Rubitherm data sheet [55], the RT18 HC's structure appears to consist of multiple hydrocarbons, with hexadecane (C\({}_{16}\)H\({}_{34}\)) being identified as the primary component. This complexity in composition and structure can lead to varied energy requirements for melting and freezing, resulting in the observed asymmetry in the thermal response. In the case of the 3 RTHC18@AC composite, the encapsulated RT18 HC melts at a lower temperature, at 18.1 \({}^{\circ}\)C (\(-1.5\) \({}^{\circ}\)C), and freezes at higher temperature, at 10.6 \({}^{\circ}\)C (\(+2.4\) \({}^{\circ}\)C). The corresponding enthalpies of pure RT18 HC and RT18 HC encapsulated on activated carbon were calculated using the areas under the exothermic (melting) and endothermic (solidification) transition peaks in their respective DSC curves.