## 4 Conclusions  
This study optimised the coagulation bath size for producing co-axial Phase Change Fibres (PCFs), ensuring their structural, chemical, and thermal performance. The ATR-FTIR area index analysis of uniaxial (F\({}_{\text{uni}}\)) and hollow (F\({}_{\text{hol}}\)) fibres confirmed that longer coagulation baths enhanced DMF solvent removal. However, excessive bath lengths (1.25 m) induced structural stress in hollow fibres, compromising integrity. An optimal bath length of 1.00 m was identified to balance efficient solvent removal and fibre stability. Morphological analysis confirmed the successful encapsulation of PEG cores within the CA sheath, with homogeneous core-sheath structures observed in all PCFs. ATR-FTIR further verified the significant reduction in DMF, demonstrating the efficiency of the optimised coagulation bath in improving fibre quality. Thermal analyses (TGA and DSC) revealed that PCFs maintained thermal stability at temperatures between ~264 \({}^{\circ}\)C and ~397 \({}^{\circ}\)C for PEG 600-based fibres and ~273 \({}^{\circ}\)C and ~413 \({}^{\circ}\)C for PEG 1000-based fibres. DSC results confirmed that PEG 600-based PCFs exhibited melting temperatures _of_ ~12.64 \({}^{\circ}\)C and ~11.04 \({}^{\circ}\)C, while PEG 1000-based PCFs showed values _of_ ~40.32 \({}^{\circ}\)C and ~41.13 \({}^{\circ}\)C, validating their phase change behaviour. These findings suggest that PCFs with PEG 600 are suitable for mild climates, while PCFs with PEG 1000 are better suited for high-temperature applications due to their greater thermal stability. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Peak** & **Enthalpy** & **Peak** & **Enthalpy** \\  & **Conset** & **Endo** & **Endset** & **Endset** \\  & (\({}^{\circ}\)**C**) & **(J/g)** & (\({}^{\circ}\)**C**) & **(J/g)** \\ \hline PEG 1000 & 41.24 & 93.62 & 26.59 & 112.96 \\ PCF:50/1000\_90\_140 & 40.32 & 83.47 & 26.95 & 84.66 \\ PCF:50/1000\_90\_150 & 41.13 & 98.88 & 28.35 & 88.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermal properties of PEG 1000 and four PCFs. These results reinforce the potential of PCFs for thermoregulation in civil engineering applications, where their thermal properties allow them to adapt to different climatic conditions. For optimal performance, the selection and optimisation of PCFs must consider structural demands and climatic conditions. In tropical regions, they limit heat absorption during the day and release it at night, mitigating the Urban Heat Island (UHI) effect and improving energy efficiency. They function as thermal regulators in colder climates, reducing heat loss and heating demands. Furthermore, the thermal stability demonstrated by TGA and DSC analyses confirms their long-term reliability for applications such as thermoregulated cement mortars. An important aspect to be investigated is the potential to increase the mechanical strength of composite materials since the sheath-core structure improves durability and resistance to thermal and mechanical stresses. Therefore, future research should prioritize mechanical performance assessments, including Dynamic Mechanical Analysis (DMA) and tensile testing, to validate structural resilience under real-world conditions. In addition, Energy Dispersive Spectroscopy (EDS) and Surface Plasmon Resonance (SPR) could further investigate the potential molecular interactions between CA and PEG. SPR, in particular, can provide valuable insights into the bonding dynamics of these materials. Finally, integrating PCFs into cementitious materials and evaluating their performance in simulated urban environments will be essential for confirming their practical applicability in sustainable construction. Conceptualisation, N.H.; methodology, I.R.S. and H.P.F. ; software, N.H., J.M. and M.M.S. ; validation, J.C.; formal analysis, N.H., I.R.S. and H.P.F. ; research, N.H., I.R.S. and J.C.; resources, M.M.S., M.F.M.C. and J.C.; data curation, N.H. and M.F.M.C.