## 3 Results and Discussion
### Characterization of Flax Yarns After Enzymatic Treatment
After the enzymatic treatment, a change in the thermal stability of the flax yarns occurred. The thermogravimetric analysis proved the enzymatic removal of hemicellulose and pectin components from the flax surface. In particular, the thermal stability of the flax yarns treated using the maximum concentration of 10 wt % of Peclyve was investigated. The thermograms reported in Figure 7 show that the peak related to water loss remained unchanged. However, the second step of the thermal degradation changed. In fact, contrary to the as-received flax, both the yarns treated for 4.5 h and 6 h did not show any step \begin{table}
\begin{tabular}{c c c} \hline \hline
**Fax Yarn** & **Treatment Time** & **Cellulose Crystallinity index (CI)** \\ \hline Neat & - & 1.01 \\ Peclyve 2.5 wt \% & 3 h & 1 \\ Peclyve 2.5 wt \% & 4.5 h & 1.15 \\ Peclyve 2.5 wt \% & 6 h & 1.24 \\ Peclyve 10 wt \% & 3 h & 1.36 \\ Peclyve 10 wt \% & 4.5 h & 1.54 \\ Peclyve 10 wt \% & 6 h & 1.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The crystallinity index of cellulose for the neat and enzymatically modified flax yarns using different times and Peclyve loads. of weight loss associated with hemicellulose and the pectin decomposition. From the mass loss vs. temperature curves, it can be also seen that the onset degradation temperatures tended to increase after the enzymatic treatment compared with the untreated flax yarns, again confirming the removal of thermally liable constituents [29]. Table 4 summarizes the maximum degradation temperature and the temperature of 10% weight loss for the untreated and the treated flax yarns. The enzymatically treated flax yarns displayed a maximum degradation temperature only slightly lower compared to that of the untreated ones, despite the removal of components that could result in a weaker macrostructure because of the disorder in bonding within the network [44]. An increase in the 10% weight loss temperature was obtained after both enzymatic treatments. In particular, the highest temperature value (325.5 \({}^{\circ}\)C) was obtained for the flax yarn after a 6 h treatment. It was not possible to detect by thermogravimetric analysis any significant effect related to the lignin removal. Lignin decomposes slower and over a broader temperature range (200-500 \({}^{\circ}\)C) compared to cellulose and the hemicellulose [45]. Flax fibres are usually characterized by a low amount of lignin, which is kept low because it enables an easier extraction of the fibres from the stem [1]. Therefore, even the untreated flax fibres did not display a marked degradation peak for the lignin in the 400-500 \({}^{\circ}\)C temperature range. The mechanical properties of neat and enzymatically treated flax yarns were addressed by a single yarn tensile test and the results were statistically analyzed using the Weibull distribution (Equation (1)):  
\[Pr(\sigma)=1-exp\left[-\left(\frac{\sigma}{\sigma_{0}}\right)^{m}\right], \tag{1}\]  
where \(Pr(\sigma)\) represents the cumulative probability of failure as a function of applied stress \(\sigma\), \(m\) is the Weibull modulus and \(\sigma_{0}\) is the characteristic strength. The failure probability (\(P_{f}\)) was estimated in accordance with Equation (2):  
\[P_{f}=\frac{i-0.5}{N}, \tag{2}\] \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Maximum Degradation** & **Temperature of 10\%** \\  & **Temperature** [\({}^{\circ}\)**C] & **Weight Loss** [\({}^{\circ}\)**C] \\ \hline Flax yarn (neat) & 357.2 & 311.3 \\ Pcedyve 10 wt \%-4.5 h & 355.7 & 322.8 \\ Pcedyve 10 wt \%-6 h & 356.7 & 325.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the thermogravimetric analysis for the different types of flax yarns. Figure 7: Derivative thermogravimetry (dTG) curves and thermogravimetric analysis (TGA) thermograms of flax yarns before and after enzymatic treatment. where \(N\) is the number of filaments tested and \(i\) is the rank of the data point for each filament.