## 3 Results
### Chemical Analyses  
The FTIR spectra analysis was performed to evaluate the effectiveness of the production process with the optimised coagulation bath, especially the reduction of the DMF  
Figure 6: Micrographs of the morphology of PCFs obtained by Bright-field microscopy, with a magnification of 5\(\times\). (**a**) PCF:50/600_90_140; (**b**) PCF:50/600_90_150; (**c**) PCF:50/1000_90_140; (**d**) PCF:50/1000_90_150.  
solvent, and to confirm the presence of PEGs in the core of the well-defined core-sheath structures. Thus, through the transmittance spectra of the four PCFs compared to the pristine materials (Figure 7a,b), it was possible to identify the functional groups characteristic of each component.  
The characteristic peaks related to the pristine CA were observed in all PCFs. The peak at \(\sim\)1745 cm\({}^{-1}\), attributed to the stretching of the carbonyl (C=O), indicates that the protective sheath was successfully precipitated, preserving the chemical properties of the CA during the production process [35]. Additionally, the peak at \(\sim\)1238 cm\({}^{-1}\), responsible for the elongation of the ester bond in the CA molecule (C-O-C), reinforces the conclusion that the polymer has not disintegrated, which is essential for the efficient encapsulation of the core [36]. The peaks at \(\sim\)1047 cm\({}^{-1}\) and \(\sim\)901 cm\({}^{-1}\) confirm the post-fabrication structural integrity of the fibre [14] through the presence of typical C-O stretching vibrations found in cellulose derivatives and the out-of-plane vibration of the glycosidic ring, consolidating the polysaccharide character of the fibre, respectively [37]. Therefore, the maintenance of CA peaks in PCFs, with consistent intensities, may suggest that the sheath was formed to protect the core.  
Figure 7: ATR-FTIR spectra of the PCFs. (**a**) PCF:50/600_90_140, PCF:50/600_90_150, pristine materials CA (Mn 50,000), and PEG 600; (**b**) PCF:50/1000_90_140, PCF:50/1000_90_150, pristine materials CA (Mn 50,000), and PEG 1000.  
Regarding the primary analysis, referring to the presence of PEGs in the PCF core, the peaks at \(\sim\)2885 cm\({}^{-1}\) and \(\sim\)1456 cm\({}^{-1}\) are associated with stretching and deformation of the C-H bonds in methylene groups (-CH\({}_{2}\)) [38; 39], which confirms the presence of PEGs (600 and 1000) in the encapsulated core. The peaks at \(\sim\)1296 cm\({}^{-1}\) and \(\sim\)1093 cm\({}^{-1}\) correspond to the stretching of the C-O-C ether bond chains [38; 39]. The definition of these peaks may suggest that the core was formed efficiently, but the repositioning observed in the peaks at 1456 cm\({}^{-1}\) and 1340 cm\({}^{-1}\) in the PCFs, compared to the pristine PEGs, may indicate molecular interactions between the core and the protective sheath. These possible interactions may justify the reduced diameter of the core observed in the micrographs of the PCFs produced. The peak at \(\sim\)945 cm\({}^{-1}\) is associated with an out-of-plane C-H deformation represented by the movement of the PEG polymer chains [39]. The differences in intensity between the spectra of PCFs produced with PEGs (600 and 1000) can be attributed to their intrinsic characteristics, molecular mass, and viscosity [38; 39]. These differences can impact the encapsulation efficiency.  
Another essential aspect to be mentioned is that the decrease in the characteristic peak of the DMF solvent was evaluated at \(\sim\)1657 cm\({}^{-1}\), belonging to the carbonyl group (C=O) [29]. In other words, the PCF samples were produced in the optimised coagulation bath, significantly reducing this peak. Finally, the reduction in the DMF peak and the well-defined presence of the CA and PEGs peaks (600 and 1000) confirm the efficiency of the process and the formation of PCFs suitable for applications in civil engineering materials and thermoregulatory systems.