Effect of treatment temperature on structures and properties of flax rove in supercritical carbon dioxide

In this study, flax rove was treated in supercritical carbon dioxide. The effect of different treatment temperatures on the surface morphology, chemical and crystal structures, and thermal properties, as well as isolated compounds of flax rove, were investigated by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal analysis, and nuclear magnetic resonance (NMR), respectively. The results showed that more mild grooves and stripes appeared on the surface of the treated flax fibers after supercritical carbon dioxide treatment. FT-IR spectra showed that hydrolysis of macromolecule of flax fibers occurred, producing a C≡C group. XRD spectra confirmed that the crystallinity of the treated flax samples was gradually increased with the raising of treatment temperature. Simultaneously, thermo gravimetric analyzer (TGA), differential thermal gravity (DTG) and differential scanning calorimetry (DSC) analysis indicated that the thermal properties of flax rove were improved with the increase of treatment temperature. In addition, NMR analysis proved that lignin and the monosaccharide composition of isolated compound were extracted from flax rove. Moreover, a predominance of β–O–4’ arylether linkages, followed by β–5’ phenylcoumaran and β–β’ resinol-type linkages for lignins of isolated compound was shown in NMR. Therefore, the results confirmed that it is technically feasible to using supercritical carbon dioxide to conduct the scouring and bleaching of flax rove.