# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 3 Results
### Morphology  
At this point, only the fibres with the best performance in terms of wet spinning production were analysed. Figure 7 illustrates the morphology of these 13 fibres, where direct observation revealed that PCFs_30_30 have a more rounded, cylindrical shape. This can be explained by the differences in concentration (30 wt. % (Mn 30,000) versus 10 wt. % (Mn 50,000)). The production of PCFt with recycled CA in the sheath and PEG2000 in the core was an innovation that encompassed everything from the solution phase to ejection by wet spinning.  
Figure 6: A flowchart explaining the selection of the best samples.  
These fibres were then measured for thickness (Figure 8) using ImageJ software. As can be seen in Figure 8, of the 29 fibres analysed, only 13 had a uniform morphology and a visible core. The main difference between CA with Mn 30,000 and Mn 50,000 is in the molar mass of the CA molecules [42; 43]. In more practical terms, this difference in molar mass can affect the material's properties, such as its solubility, viscosity, and mechanical strength.  
The different types of fibre structure were observed by SEM, as shown in Figure 9. In general, the structures have an expected shape, where Fu, being uniaxial, has a cylindrical structure. In comparison, Fu has a coaxial hole, albeit a small one, which could be affected by the fact that it was filled with dH\({}_{2}\)O; when it met the coagulation bath, as it did not have a core structure, the structure collapsed and flattened. The PCF composed of CA (Mn 30,000) in the sheath and PEG2000 in the core had a more cylindrical structure with a larger opening compared to the PCF composed of CA (Mn 50,000) in the sheath and PEG2000 in the core, which not only had a smaller coaxial structure but also had a flattened structure. In addition, the PCFt with a PEG2000 with an 80% concentration in the core showed a similar (albeit less uniform) structure to the PCF_50, with the same PEG2000 concentration.  
The presence of PEG2000 inside the PCFs is not noticeable and can be explained by a few possible factors. Firstly, as PEG2000 is diluted in dH\({}_{2}\)O and is in liquid form, when cutting the PCF samples for SEM, the PEG could leak out. Another viable option is the potential evaporation of the polymer during vacuuming. It is also likely that the magnification of the test was not big enough to detect the PEG2000 in contact with the CA and CA sheath. Even though PEG detection was not possible, the goal of this test was the visualisation of the coaxial fibres, which was achieved.  
Figure 7: Micrographs of the morphology of the hollow and PEG2000-incorporated fibres obtained by brightfield microscopy. **(a)** Fh\(\_\)30\(\_\)30; **(b)** PCF\(\_\)30\(\_\)10/60\(\_\)150; **(c)** PCF\(\_\)30\(\_\)10/80\(\_\)150; **(d)** PCF\(\_\)30\(\_\)20/40\(\_\)140; **(e)** PCF\(\_\)30\(\_\)30/40\(\_\)130; **(f)** PCF\(\_\)30\(\_\)30/40\(\_\)140; **(g)** PCF\(\_\)30\(\_\)30/40\(\_\)150; **(h)** PCF\(\_\)30\(\_\)30/80\(\_\)150; **(i)** Fh\(\_\)50\(\_\)10; **(j)** PCF\(\_\)50\(\_\)10/40\(\_\)130; **(k)** PCF\(\_\)50\(\_\)10/40\(\_\)140; **(l)** PCF\(\_\)50\(\_\)10/80\(\_\)140; **(m)** PCF\(\_\)50\(\_\)10/80\(\_\)150; **(n)** Fht\(\_\)8; **(o)** PCF\(\_\)8/40\(\_\)100; **(p)** PCF\(\_\)8/80\(\_\)120.  
Figure 8: Calculation of the thickness of the fibres produced by wet spinning with a detailed analysis of the uniformity and presence of the visible core. Data presented as mean \(\pm\) SD (\(n\) = 5).  
Figure 9: SEM micrographs of the Fu, Fh, PCF and PCFt. (**a**) Fu_30_30; (**b**) Fu_30_30; (**c**) PCF_30_30/40_140; (**d**) PCF_50_10/40_140; (**e**) PCF_50_10/80_150; (**f**) PCFt_8/40_100.