## 3 Results
### Thermal Analyses
#### 3.4.2 Differential Scanning Calorimetry (DSC)
Although the melting temperatures suffered a slight decrease, the influence of dH\({}_{2}\)O will be minor for the crystalline structure of PEG 1000 because the material presents longer and more stable polymer chains, which result in enthalpy values relatively close to those of the pristine material [39]. In the cooling phase, PEG 1000 presented a crystallisation temperature of 26.59 \({}^{\circ}\)C and an exothermic (exo) enthalpy of 112.96 J/g [25]. Meanwhile, the PCFs exhibited slightly higher crystallisation temperatures of 26.95 \({}^{\circ}\)C and 28.35 \({}^{\circ}\)C, with enthalpies of 84.66 J/g and 88.79 J/g, respectively. This behaviour can be attributed to the encapsulation process of PEG 1000 in these PCFs, stabilising the nucleation and alignment of the PEG polymer chains, resulting in a slight increase in the crystallisation temperature [48]. Figure 10: DSC curves of the pristine materials (CA and PEG 1000) and PCFs 1000, obtained from 80 to \(-\)30 \({}^{\circ}\)C under an Ar atmosphere, a calibrated flow rate of 50 mL/min, and exposed to a heating/cooling rate of 10 \({}^{\circ}\)C/min. Figure 9: DSC curves of the pristine materials (CA and PEG 600) and PCFs 600, obtained from 80 to \(-\)30 \({}^{\circ}\)C under an Ar atmosphere, a calibrated flow rate of 50 mL/min, and exposed to a heating/cooling rate of 10 \({}^{\circ}\)C/min. The results presented for the DSC test are connected to those presented for the TGA test since both reinforce the influence of dH2O on the thermal stability of the PCFs and their encapsulation. While the TGA test demonstrated a reduction in the degradation temperatures of the encapsulated PEGs, the DSC test directly impacted the heat storage capacity due to the decrease in crystallinity and enthalpy in the respective PCFs. However, the protection that the CA sheath provides is sufficient to preserve the thermoregulatory characteristics of the PEGs. Therefore, these thermoregulatory characteristics of the PEGs incorporated in the PCFs highlight their potential applications. For example, PCFs with PEG 600, with lower melting and crystallisation temperatures, are suitable for regions with moderate climates since they can release heat at lower temperatures, providing continuous thermal regulation at night. Meanwhile, PCFs with PEG 1000, with more excellent thermal and enthalpy stability, for example, show promising performance for regions with higher temperatures, where the ability to store heat for extended periods is required. Compared with the study by [PERSON] et al. [34], the encapsulation of PEG within co-axial fibres resulted in a significant improvement in thermal stability, as observed in the DSC test. The PCFs presented well-defined phase transitions and high enthalpies of fusion and crystallisation, reducing the supercooling effect and ensuring efficient heat storage and release throughout the thermal cycle. Therefore, these results corroborate the findings in the literature, evidencing that the core-shell structure plays an essential role in the thermal stabilisation of PEGS and their viability for civil engineering applications.