Effect of treatment pressure on wool fiber in supercritical carbon dioxide fluid

The treatment of wool in supercritical carbon dioxide fluid is an environmentally friendly and advantageous solution for cleaner production of wool textiles with water free and energy preserving, as well as avoiding a large amount of effluent discharge and serious environment pollution in conventional wet chemical processes. In the present work, some basic supports for the applications of supercritical carbon dioxide fluid in the cleaner production of wool were developed at different system pressures. The effects of treatment pressures on the crystal and chemical structures, macrochain conformations, thermal property and surface morphology of wool were investigated by employing Wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectrometry (FT-IR), thermogravimetric (TG)/differential thermogravimetric analysis (DTG) and scanning electron microscopy (SEM). The WAXD analysis indicates that an improvement of crystallization both in α-helix and β-sheet structures was obtained for wool treated at different pressures in supercritical CO2 fluid, although the improvement tendency was decreased with pressures. Moreover, a re-crystallization and a swelling of crystals in wool fiber were also occurred during the supercritical treatment. FT-IR analysis shows that more powerful interactions of hydrogen bonds between the macromolecular chains of wool were formed during the supercritical treatment, accompanying with a significant transformation of α-helix to β-sheet structure and an oxidation or acidic hydrolysis of disulfide bonds in wool scales. The TG-DTG analysis shows that an enhanced thermal stability of wool was obtained after a treatment in supercritical CO2 fluid. Moreover, a notable etching effect or dilapidation on the scales of wool was observed in SEM analysis with a decrease in scale height, thickness and coating density on fiber.