# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 3 Results
### Thermogravimetric Analysis (TGA)  
The increase in temperature associated with polymer degradation was identified in the variations in the fibres' TGA curves, as shown in Figure 11. In the initial phase, degradation was observed up to \(\approx\)100 \({}^{\circ}\)C in all the samples, with this phase corresponding to the dehydration of the samples with the elimination of the dH\({}_{2}\)O molecules (associated with humidity) [56] and potential traces of DMF and NMP solvents. As mentioned in the Materials and Methods section, the fibres were stored for 24 h in a humidity-controlled environment and, to maintain their integrity, they were subjected to TGA without the fibres being completely free of dH\({}_{2}\)O. Both the Fh and the PCFs showed thermal stability up to \(\approx\)300 \({}^{\circ}\)C and \(\approx\)350 \({}^{\circ}\)C, respectively. Thereafter, mass losses were observed, consistent with the endothermic peak recorded in the DSC around 415 \({}^{\circ}\)C (Figure 12) [57]. The fact that PCFs, which have a CA sheath and a PEG core, showed thermal stability followed by mass loss at a slightly higher temperature can be explained by the presence of PEG in their core. Thus, the decomposition of the polymer takes place in two phases, with the first degradation due to the breakdown of the PEG2000 chains and the second decomposition due to the breakdown of CA [58]. According to the literature, the pyrolysis process of PEG with a molecular weight above 1000 g/mol generally takes place at a temperature of 350 \({}^{\circ}\)C, where thermal decomposition begins at the -C-O- and -C-C- bonds of the two chains and is evident between 340 and 415 \({}^{\circ}\)C [59]. However, CA has high thermal stability, with a degradation temperature of over 300 \({}^{\circ}\)C [58].  
Considering that the PCFs with the best performance were selected, both visually and through mechanical and thermal tests, the results presented by the TGA analysis may be associated with the diameter of the PCFs. The PCFs with Mn 30,000 CA in the sheath had a more cylindrical shape, thus better preserving the PEG at their core, while the PCFs with Mn 50,000 CA showed flattening, which may have compromised the thermal stability of the PCFs (as evidenced in the DSC data) and resulted in a slightly greater loss of mass [24].  
Finally, regarding the TGA analysis for PCFt, as with the PCFs, degradation up to \(\approx\)100 \({}^{\circ}\)C was recognized in all the samples, where the extent of this step corresponds to the dehydration of the samples with the elimination of the dH\({}_{2}\)O molecules and the NMP solvent present during production. CA synthesized with a degree of substitution of 2.90 registers the most important degradation step at 350-360 \({}^{\circ}\)C [55; 60]. Therefore, the results for PCFt with a degree of substitution of 2.83 are in line with the literature and show similar thermal behaviour with a degradation temperature of \(\approx\)350 \({}^{\circ}\)C.  
Figure 11: TGA 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.