## 3 Results and Discussion
### Characterization of Flax Yarns After Enzymatic Treatment
Figure 3: SEM micrographs of the flax yarns as a function of the different enzymatic treatments with Peclyve: (**A**) 2.5 wt %, 4.5 h; (**B**) 2.5 wt %, 6 h; (**C**) 5 wt %, 4.5 h; (**D**) 5 wt %, 6 h; (**E**) 7.5 wt %, 4.5 h; (**F**) 7.5 wt %, 4.5 h; (**F**) 7.5 wt %, 6 h; (**G**) 10 wt %, 4.5 h; (**H**) 10 wt %, 6 h.  
Figure 4: SEM micrograph of the flax yarn treated with 10 wt % Peclyve for 4.5 h. The micrograph shows the damage to the outer fibres of the flax yarn after the enzymatic treatment. Figure 5: Infrared spectra of neat (**a**) and enzymatically modified flax yarns using 2.5 wt % Peclyve for 3 h (**b**), 4.5 h (**c**) and 6 h (**d**). Figure 6: Infrared spectra of neat (**a**) and enzymatically modified flax yarns using 10 wt % Peclyve for 3 h (**b**), 4.5 h (**c**) and 6 h (**d**). Comparing the infrared spectra of the flax yarns enzymatically treated using a 2.5 wt % Peclyve solution for different durations (Figure 5), it is possible to notice that the longer the treatment time, the greater the removal efficiency of the enzymatic solution. The lowest hemicellulose and pectin bands were obtained after a treatment duration of 6 h (Figure 5d). These results are supported by the crystallinity index (CI) of cellulose, which was measured for the different flax yarns. Higher values of CI are associated with a greater amount of crystalline cellulose, thus confirming the ability of the enzymatic treatment to extract amorphous components [39; 40]. In this work, a semiquantitative measurement of the CI of cellulose (Table 3) is presented, expressed as the intensity ratio between the IR absorption bands at 1427 and 897 cm\({}^{-1}\) (1427/1897), which belong to the CH\({}_{2}\) bending mode of cellulose and to the CH in \(\beta\)-glycosidic linkages between monosaccharides [41]. A progressive increase in the cellulose crystallinity index values was observed passing from the 3 h to the 6 h treatment. Concerning the infrared spectra of the flax yarns modified using a 10 wt % Peclyve solution (Figure 6), an additional reduction in the hemicellulose and lignin bands occurred. Negligible differences could be found between the infrared spectra of the flax yarns treated for 4.5 h and 6 h, and the same cellulose CI value was measured. These results highlight that the use of the Peclyve solution with a concentration of 10 wt % allowed the maximum efficiency to be obtained after 4.5 h of treatment. No further removal of amorphous components from the surfaces of the flax fibres was produced using longer treatment times. [PERSON] and [PERSON] [29] reported the same trend in hemp fibres treated with combinations of pectinase and lacase with and without the presence of a chelator (ethylenediamine tetra(methylene phosphonic acid), EDTMPA). With a progressive removal of amorphous non-cellulosic compounds, the authors found a significant increase in the crystallinity index evaluated by the Segal method after enzymatic treatment, which passed from 66.3% to 86.3% for the raw and treated hemp fibres, respectively. Figure 7 displays the representative thermographs, expressed as the mass loss and derivative mass loss for the neat and enzymatically treated flax yarns. The neat flax yarns were characterized by the well-known three stages of degradation that depend on the different thermal stabilities of their constituents, i.e., cellulose, hemicellulose and lignin. While the first mass loss in the range of 60-120 \({}^{\circ}\)C is due to the absorbed water, the additional two peaks at about 240-280 \({}^{\circ}\)C and 340-360 \({}^{\circ}\)C are ascribed to the degradation of pectin and hemicellulose and to cellulose, respectively [42; 43]. Hemicellulose and pectin in lignocellulosic fibres decompose at a lower temperature than cellulose and lignin [21], therefore it can be assumed that the removal of the less thermally stable hemicellulose and pectin by enzymatic treatment, as confirmed by the FT-IR measurements, would improve the thermal resistance of the treated flax yarns.