# Coaxial Fibres Incorporated with Phase Change Materials for Thermoregulation Applications
## 3 Results
### Mechanical Behavior  
The maximum elongation and maximum breaking strength of the Fh and PCF fibres produced by wet spinning were analysed using 10 cm long filaments (Table 4). This test was carried out to assess and observe the mechanical strength of the fibres. The fibres that did not show uniformity and a visible core could not be examined, since after the production, they were flattened and open; this is due to the fibre collapsing into its hollow interior and possible clogging of the needle. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Maximum Elongation at** & **Breaking Strength** \\  & **Break (\%)** & **(kPa)** \\ \hline Fh\_30\_30 & 28.86 \(\pm\) 1.59 & 133.18 \(\pm\) 6.57 \\ PCF\_30\_10/60\_150 & 1.59 \(\pm\) 0.14 & 105.54 \(\pm\) 14.73 \\ PCF\_30\_10/80\_150 & 2.46 \(\pm\) 0.30 & 212.83 \(\pm\) 52.80 \\ PCF\_30\_20/40\_140 & 14.32 \(\pm\) 0.22 & 1023.64 \(\pm\) 52.56 \\ PCF\_30\_30/40\_130 & 28.46 \(\pm\) 1.08 & 1094.60 \(\pm\) 150.04 \\ PCF\_30\_30/40\_140 & 22.42 \(\pm\) 0.84 & 1122.49 \(\pm\) 145.56 \\ PCF\_30\_30/40\_150 & 13.07 \(\pm\) 0.93 & 920.01 \(\pm\) 104.02 \\ PCF\_30\_30/80\_150 & 25.40 \(\pm\) 0.63 & 264.68 \(\pm\) 22.18 \\ Ph\_50\_10 & 16.50 \(\pm\) 0.95 & 117.28 \(\pm\) 30.03 \\ PCF\_50\_10/40\_130 & 11.71 \(\pm\) 0.60 & 60.28 \(\pm\) 5.86 \\ PCF\_50\_10/40\_140 & 16.20 \(\pm\) 0.99 & 100.63 \(\pm\) 13.22 \\ PCF\_50\_10/80\_140 & 12.98 \(\pm\) 0.58 & 75.03 \(\pm\) 17.68 \\ PCF\_50\_10/80\_150 & 21.62 \(\pm\) 0.42 & 105.69 \(\pm\) 15.68 \\ Fht\_8 & 4.00 \(\pm\) 0.71 & 61.36 \(\pm\) 18.46 \\ PCFt\_8/40\_100 & 7.18 \(\pm\) 0.62 & 28.06 \(\pm\) 14.20 \\ PCFt\_8/80\_120 & 9.02 \(\pm\) 0.66 & 39.75 \(\pm\) 9.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical testing of wet spinning fibres. Data presented as mean \(\pm\) SD (\(n\) = 5). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Peak Temperature** & **Melting Point** \\  & **(\({}^{\circ}\)C)** & **(J/g)** \\ \hline Fh\_30\_30 & 139.84 & 111.78 \\ Fh\_50\_10 & 134.42 & 140.46 \\ Fht\_8 & 137.52 & 134.39 \\ PCF\_30\_20/40\_140 & 78.02 & 108.43 \\ PCF\_30\_30/40\_130 & 72.26 & 56.38 \\ PCF\_30\_30/40\_140 & 64.87 & 50.51 \\ PCF\_50\_10/40\_140 & 61.61 & 70.91 \\ PCF\_50\_10/80\_150 & 74.96 & 106.40 \\ PCFt\_8/40\_100 & 69.83 & 44.97 \\ PCFt\_8/80\_120 & 72.84 & 41.52 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thermal properties of Fh, Fht, PCF, and PCFt. Reports have addressed the poor mechanical properties of CA alone as an obstacle to many applications [66]. However, this does not significantly influence PCFs, since the final application depends on the properties of the CA, PEG, and PCF composites working together. The tensile properties of wet-spun fibres can be affected by different factors, such as the concentration of the CA, the direction of the test, the concentration of the solution, and so on [34]. In this work, the tensile properties of PCFs and PCFt composed of CA and CAt in the sheath and PEG2000 in the core were measured, examining the extent to which the concentrations of CA and PEG can influence the final data. The cross-sectional area of the fibres was measured using bright-field microscopy (Figure 8), and from those values, the stress (kPa) could be calculated for each of the fibres. The maximum stress-stretch values for Fh and PCFs are shown in Table 4.  
The mechanical properties of PCFs are also sensitive to the acetyl content; the tensile strength and modulus of elasticity are higher in CA with lower molecular weights and higher concentrations. This indicates that increased acetylation produces a stronger and stiffer material. The glass transition decreases as the degree of acetylation increases, reflecting the reduced fraction of the amorphous phase [38]. Following the reasoning in the literature, comparisons between PCFs--where the difference was in the molecular weight of the CA--showed that fibres with a molecular weight of Mn 30,000 exhibit higher tensions while fibres with Mn 50,000 show considerably lower values.