# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 2 Materials and Methods
### Fibres' Production  
Solutions of CA (10-20-30 wt. %) and PEG2000 at (40-60-80 wt. %) were prepared overnight in DMF and dH\({}_{2}\)O, respectively, both being stirred continuously at 50 \({}^{\circ}\)C. Meanwhile, the CAt (8 wt. %) solutions were prepared overnight in NMP under moderate stirring at 50 \({}^{\circ}\)C. Prior to the wet spinning production, the solutions were left to stand at room temperature for 1 h to remove any air bubbles.  
For all productions, the wet spinning setup consisted of a syringe pump NE-1000 (New Era Pump Systems Inc., Farmingdale, NY 11735, EUA), a coagulation bath of dH\({}_{2}\)O at room temperature, a collector, and a needle (uniaxial or coaxial and one/two syringes connected to the pump, with the latter two parameters adjusted according to the type of fibre produced). A representative schematic of the wet spinning process is shown in Figure 4. The fibre collector consisted of aluminium foil wrapped around an automatic collector at a moderate velocity of 6.21 rpm. The distance between the collector and the needle was 45 cm, and the distance between the needle and the coagulation bath was 5 cm.  
To produce uniaxial fibres (Fu) and uniaxial CAt fibres (Fu), a wet spinning configuration was applied, but the needle used for the process was uniaxial, requiring only one pump and adjusted according to ejection parameters. To produce hollow fibres (Fh), hollow CAt fibres (Fht), and PCF and coaxial CAt fibres (PCFt), the only parameter that differed was the needle, which instead of being a single needle was replaced by a coaxial needle. Meanwhile, for Fh and Fht only, the outermost port was used with the solution of CA and CAt, respectively. In contrast, for PCF and PCFt, the outermost port was used for CA and CAt, respectively, and the innermost port for PEG2000.  
The parameters of the wet spinning process were adjusted to obtain fibres with better properties [39] and are demonstrated in Figure 5. The ejection velocity for CA was 0.165 mL/min, while for PEG2000, it varied from 0.130 to 0.140-0.150 mL/min. Fibres with CAt and PEG2000 were produced with slightly lower ejection velocities, namely 0.130 mL/min for CAt and (0.100-0.120 mL/min) for PEG2000. In the case of coaxial fibres, CAt required different ejection velocities to obtain enough time to compose a coaxial system with a protective sheath.  
Figure 4: Scheme of production of PCFs via wet spinning.  
After production, all fibres were passed through dH\({}_{2}\)O to remove any traces of solvent (DMF and NMP) and dried for 1 h at room temperature. The fibres were then stored at room temperature and humidity for subsequent testing. A qualitative analysis was carried out during the production of the fibres by wet spinning, which considered whether the fibres could be extruded easily, whether there was surface roughness, and whether the fibres were extruded uniformly. This analysis is presented in the results and discussions.  
PEG being soluble in dH\({}_{2}\)O guarantees its incorporation into the fibre. When dH\({}_{2}\)O meets the walls of the protective sheath, coagulation occurs, forming a resistant inner wall to fix the substance. Although there are not yet many reports on wet-spun coaxial fibres with this type of structure, it is hoped that research will progress in this direction.