| Due to the high energy consumption and pollution of traditional textile desizing pretreatment,a clean and efficient desizing method is urgently needed to change this situation.A green desizing method was developed for textile pretreatment by the reaction medium of supercritical CO2 fluid,which could effectively reduce the dosage of chemicals and wastewater emissions.It has a great significance for textile industry to realize the reduction of energy-saving emission and cleaner production.In this paper,the influences of amount of bis(2-ethylhexyl)sulfosuccinate sodium(AOT),relative volume fraction of ethanol(vol.%),content of water(vol.%),temperature,pressure and processing time on the formation and stability of microemulsion were investigated by employing the solvatochromic probe in supercritical CO2 fluid.Then,the effects of hydrogen peroxide,dosage of buffer solution,the value of p H,AOT,dosage of ethanol,temperature,pressure and processing time on the desizing results of cotton fabrics were discussed in the supercritical CO2 microemulsion system for optimizing the desizing condition.Moreover,the effects of amount of sodium percarbonate,tetraacetyl ethylenediamine(TAED),temperature,pressure and processing time on desizing of cotton fabric also were discussed for optimizing the desizing condition.Furthermore,the phase transfer oxidative desizing process of cotton fabric was investigated in supercritical CO2 fluid by a phase transfer catalyst 18-crown-6,and a suitable desizing process was obtained.In addition,the effects of dosage of soap solution,temperature,pressure and processing time in supercritical CO2 fluid on the cleaning effect of desizing cotton fabric were discussed by employing the method of emulsification of soapy liquid for optimizing the cleaning condition.Finally,the surface morphology,chemical structure,the aggregation structure,water absorption,heat resistance and the surface chemical composition of the treated cotton fiber were analyzed by employing the scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),X-ray powder diffraction(XRD),contact angle measurements,Thermogravimetric(TG)/differential thermogravimetric analysis(DTG)and X-ray photoelectron spectrometer(XPS),respectively.The results show that the methyl orange(MO)was extracted into the supercritical CO2 microemulsion formed by the surfactant of AOT,and the maximum absorption wavelength of MO was shifted greatly to low wave number.The supercritical CO2 microemulsion could be formed at the concentration of AOT at 0.0005~0.01 mol L-1,relative volume fraction of ethanol at 0.50~22.3%,relative volume fraction of water at 0.43~2.70%,pressure of 14~22MPa and temperature of 35~95℃.Moreover,a more stable supercritical CO2 microemulsion system could be obtained at the concentration of AOT at 0.01 mol L-1,relative volume fraction of ethanol at 15.60%,relative volume fraction of water at 1.30%,temperature of 55℃ and pressure of 18 MPa.Meanwhile,good results obtained in the desizing of grey cotton fabric by employing the supercritical CO2 microemulsion system with oxidative desizing treatment,show that oxidative desizing in supercritical CO2 fluid is feasible.In this experimental system,the optimized hydrogen peroxide desizing process condition in supercritical CO2 fluid is recommended as: 12.5m L/L hydrogen peroxide solution,10 m L/L buffer solution,the p H of buffer solution at 11,0.3g/L AOT,7.5m L/L ethanol,the temperature at 85°C,the pressure at 20 MPa and processing time ranged from 60 min to 120 min.In addition,the weight loss rate and the value of capillary height of cotton fabric were 4.82% and 10.2cm at the optimized hydrogen peroxide desizing process condition,respectively.Furthermore,the optimized sodium percarbonate desizing process condition in supercritical CO2 fluid is recommended as: 3g/L sodium percarbonate,0.75g/L TAED,0.3g/L AOT,5m L/L ethanol,20 m L/L water,the temperature at 80°C,the pressure at 20 MPa and processing time of 90 min.The weight loss rate and the value of capillary height were 5.34% and 11.3cm at the optimized sodium percarbonate desizing process condition in supercritical CO2 fluid,respectively.Good results from the desizing of grey cotton fabric by employing the phase transfer oxidative desizing in supercritical CO2 fluid,show that the phase transfer oxidative desizing is available.The optimum phase transfer oxidative desizing process condition in supercritical CO2 fluid is recommended as:10m L/L hydrogen peroxide solution,7.5m L/L buffer solution,the p H of buffer solution at 11,0.005mol/L 18-crown-6,0.5g/L TAED,the temperature at 70°C,the pressure at 18 MPa and processing time of 60 min.Besides,the weight loss rate and the value of capillary height of cotton fabric were 6.21% and 8.0cm under the preferred desizing process condition,respectively.Good cleaning results could be obtained by employing the method of emulsification of soapy liquid in supercritical CO2 fluid.Meanwhile,the soap liquid has a significant impact on the polarity of fluid and the cleaning efficiency.The optimized cleaning process condition in supercritical CO2 fluid is recommended as: 15 m L/L soap liquid,the temperature at 80°C,the pressure at 18 MPa and processing time of 90 min.The weight loss rate could be increased by 2.63%,and the value of capillary height of cotton fabric was 8.6cm at the recommended cleanzing process condition。After phase transfer oxidative desizing and fluid cleaning treatment in supercritical CO2 fluid,the surface morphologies and properties of cotton fiber had undergone great changes.As the infrared spectra reveal that the chemical environment of chemical functional groups of cotton fiber has changed,and its characteristic group(-OH)absorption peak shifted to the lower wave number.The results of X-ray diffraction suggest that the crystal structure of cotton fiber had greatly affected,and the crystallinity was decreased.According to the results of the scanning electron microscopy,the surface of cotton fibers changed obviously.The surface of the fiber became smooth,and the natural texture became more clear.As the results shown from the contact angle test,the water absorption and wettability of cotton fiber had significantly improved.Furthermore,TG-DTG analysis results that the heat resistance of cotton fibers has decreased.The results of XPS show that the chemical composition of cotton fiber surface changed obviously,indicating that the starch covers and other impurities on the fiber were degradated and removed in supercritical desizing system. |
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