# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 3 Results
### Differential Scanning Calorimetry (DSC)  
DSC is used to study the thermal behaviour of materials and to determine enthalpy [33]. Figure 12 shows the DSC thermograms for Fh, Fht, PCFs and PCFs, in which coaxial fibres have different CA molecular weights and concentrations and different PEG concentrations and ejection velocities. Meanwhile, the corresponding thermal property data from the DSC curves are shown in Figure 12.  
At first, both Fh and Fht were subjected to DSC and, as can be seen in Figure 12, an average endothermic transition occurred around 100 \({}^{\circ}\)C, which suggests the loss of moisture absorbed from the solvents [20] and the elimination of water molecules [61]. An average peak at \(\approx\)137.26 \({}^{\circ}\)C was detected and associated with the glass transition temperature of CA [62]. Finally, a last peak was detected at \(\approx\)236.08 \({}^{\circ}\)C, which was attributed to the crystallisation of the amorphous domains of the CA chains [61]. When the PCFs and PCFs were subjected to the DSC test, different behaviour was seen, where the addition of PEG to the core of the CA and CAt fibres resulted in the appearance of an average endothermic transition at \(\approx\)38.30 \({}^{\circ}\)C and an average peak, representative of PEG, at around 70.72 \({}^{\circ}\)C, with a variation of 10 \({}^{\circ}\)C which is attributed to the exothermic crystallisation of PEG [63]. A peak at \(\approx\)89.25 \({}^{\circ}\)C was also observed because of the interactions between CA, CAt and PEG, which displaced the peak detected in the pristine CA fibres at 92 \({}^{\circ}\)C. The introduction of a plasticiser such as PEG into the core lowers the Tg of the CA polymer as it causes a reduction in intermolecular forces, generating protective effects with functional groups such as -OH [34]. The PEG acts as a working material and the CA entanglement, due to secondary interactions, hinders and disturbs the orientation of the PEG molecular chains [58]. This explains the displacement of the endothermic melting peak of PEG2000 crystallisation, since according to [PERSON] et al., this peak normally occurs in the 46-54 \({}^{\circ}\)C range. These interactions between the carbonyl of CA and the hydroxyl groups of PEG occur frequently, and this justifies the displacement of the characteristic PEG peak [63; 64]. Finally, two endothermic peaks could still be observed, the first characteristic of CA and CAt at \(\approx\)223.85 \({}^{\circ}\)C and the second referring to the PEG pyrolysis process at \(\approx\)370.55 \({}^{\circ}\)C, which generally happens around 350 \({}^{\circ}\)C, as detailed in the TGA discussion. As reported, the higher the molecular weight of PEG, the higher the temperature at which the pyrolysis process takes place, which explains the increase of \(\approx\)20.55 \({}^{\circ}\)C [59]. The peaks around 70 \({}^{\circ}\)C determined the enthalpy of phase change (Table 3). This reduction in PEG's enthalpy of phase change was due to the disturbance in PEG crystalli  
Figure 12: DSC curves of the Fh, PCF, Fht and PCFt fibres obtained from 25 to 500 \({}^{\circ}\)C under a nitrogen atmosphere, flow rate of 200 mL/min, and temperature rise of 10 \({}^{\circ}\)C/min. sation caused by the presence of CA [58]. There is a protective CA sheath, which, due to the different molecular weights and concentrations, was better formed for PCFs_30_30; consequently, PEG used less energy to change phases. Meanwhile, for PCF_50_10, as the sheath was less developed and the PCF was flatter, PEG needed more energy to change the phase. This explains why the enthalpy values were lower for PCFs_30_30. Therefore, the corresponding experimental enthalpy values for PCFs_30_30 were lower than the theoretical ones, with the decrease in enthalpy being attributed to PEG crystallisation becoming restricted and the possible entanglement between the PEG and CA molecular chains in the sheath of PCFs and PCFt [65].