## 3 Results
### Thermal Analyses
#### 3.4.2 Differential Scanning Calorimetry (DSC)  
Cyclic DSC analysis evaluated PCFs' thermal properties and behaviour and compared the results to pristine materials (PEG 600 and 1000). This thermal analysis is essential for understanding the impact of PEG incorporation and the uniformity of PCF structuring on phase changes (melting and crystallisation), indicating their heat storage and release capacity. Starting the analysis with the results for PEG 600 (Figure 9) and (Table 1), the pristine material presented a well-defined melting endothermic (endo) peak at 15.76 \({}^{\circ}\)C, with a melting enthalpy of 68.21 J/g, confirming its crystalline behaviour during melting [25; 44]. The material (PEG 600) is particularly suitable for integration into cementitious materials, where it can increase indoor thermal comfort in buildings by attenuating temperature fluctuations in temperate and mild climates. When incorporated into building materials, PEG 600 can absorb excess heat during the day and release it at night, reducing the need for active cooling [44]. However, the PCFs incorporated with this PEG 600 (PCF:50/600_90_140 and PCF:50/600_90_150) showed a reduction in the endothermic (endo) melting temperatures to 12.64 \({}^{\circ}\)C and 11.04 \({}^{\circ}\)C, accompanied by lower enthalpy values, 39.24 J/g and 30.59 J/g, respectively. This reduction can be attributed to the PEG solution to form the core (concentration of 0.90 g/mL), using dH\({}_{2}\)O in the composition, which induces the presence of hydrogen bonds between the dH\({}_{2}\)O and PEG 600 molecules, decreasing the crystallinity of the material [45]. In the same line of reasoning, dH\({}_{2}\)O also acts as a plasticiser, increasing the mobility of the polymer chains and promoting a more amorphous behaviour of the material, which results in lower thermal stability and less energy required to carry out the fusion process. In the cooling phase, PEG 600 presented a crystallisation temperature of \(-\)1.21 \({}^{\circ}\)C with two peaks and an exothermic (exo) enthalpy of 72.74 J/g [46]. These two crystallisation peaks may indicate the formation of two crystalline phases or secondary recrystallisation due to PEG 600 having a semi-crystalline structure. However, the PCFs exhibited lower crystallisation temperatures, \(-\)3.78 \({}^{\circ}\)C and \(-\)5.30 \({}^{\circ}\)C, and enthalpies with lower values of 50.17 J/g and 40.93 J/g, respectively. This time, the reduction in crystallisation temperatures can be explained by supercooling, which occurs when the material cools below its melting temperature before forming crystals [47]. Therefore, the protective CA sheath contributes to this effect by restricting the PEG 600 core and limiting its mobility, making it difficult to organise the polymer chains into a well-defined crystalline structure [14]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Peak** & **Enthalpy** & **Peak** & **Enthalpy** \\  & **Temperature** & **Endo** & **Temperature** & **Exo** \\  & **Onset** & **(**)/g** & **Endset** & **(**)/g** \\  & **(**)** & **(**)** & **(**)** \\ \hline PEG 600 & 15.76 & 68.21 & \(-\)1.21 & 72.74 \\ PCF:50/600\_90\_140 & 12.64 & 39.24 & \(-\)3.78 & 50.17 \\ PCF:50/600\_90\_150 & 11.04 & 30.59 & \(-\)5.30 & 40.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Thermal properties of PEG 600 and four PCFs. Regarding the results for PEG 1000 (Figure 10) and (Table 2), the analyses showed an initial melting temperature of 41.24 \({}^{\circ}\)C and an enthalpy of 93.62 J/g, indicating a result with more excellent thermal stability compared with that presented for PEG 600 due to its larger polymer chains and crystallinity [25; 44]. The PCFs with PEG 1000 (PCF: 50/1000_90_140 and PCF: 50/1000_90_150) exhibited melting temperatures of 40.32 \({}^{\circ}\)C and 41.13 \({}^{\circ}\)C and enthalpies of 83.47 J/g and 88.88 J/g, respectively.