Enzymatic Desizing For Cotton Pretreatment With Supercritical Carbon Dioxide Fluid

A large consumption of chemicals and discharging of a lot of wastewater from the traditional desizing pretreatment such as alkali desizing and acid desizing processes,result in serious environmental pollutions.Thus,it is very important and meaningful to investigate the the desizing pretreatment with enzymes in supercritical CO₂ fluid and its desizing processes,in order to reduce the utilization of water and chemicals,as well as to reduce the energy consumption and effluent discharge,shorten process flow,save production costs,etc.In this paper,the synergistic effect of several enzymes,the process optimization for enzymatic desizing,the kinetics of enzyme catalyzed reactions and the final cleaning of cotton fabrics,were investigated by employing supercritical CO₂ fluid medium.Firstly,according to weight loss,whiteness and capillary rise height,the effects of?-amylase,pectinase,lipase,cellulase,hemicellulase and xylanase on desizing pretreatment were studied on the basis of orthogonal experiment.Besides,the synergistic effects between?-amylase,pectinase and lipase were also explored.Secondly,the effects of treatment time,temperature,pressure and concentration of?-amylase on degradation of starch in supercritical CO₂ fluid were discussed,and the degradation process of starch by?-amylase in supercritical CO₂ fluid was also optimized according to the weight loss and capillary rise height of the substrate.Furthermore,the kinetic model of desizing process of?-amylase in supercritical CO₂ fluid was supposed.The kinetics of desizing was explored in the optimal desizing process,and the kinetic equation of desizing process was obtained.Afterwards,the effects of moisture content in supercritical CO₂ fluid,treatment time,pressure and temperature on the cleaning effect of supercritical CO₂ fluid were studied,and the cleaning process was optimized according to weightlessness and capillary rise height.Finally,the original cotton fabric,the sized cotton fabric,the cotton fabric after being desized and the samples after being cleaned in the supercritical fluid were tested and analyzed.The surface morphology and surface element ratio of cotton fibers were observed by scanning electron microscopy?SEM?and supporting energy dispersive spectrometer?EDS?.The conformation changes of macromolecules and surface wettability of cotton fiber were confirmed by Fourier transform infrared?FT-IR?spectra and contact angle measurement,respectively.The results show that?-amylase,pectinase and lipase have some synergistic effects in the desizing process when they were used to desize grey cotton at the same time in the supercritical CO₂ fluid.Specifically,synergistic effects on fabric weight loss between?-amylase and pectinase,as well as on fabric whiteness between?-amylase and lipase,on fabric whiteness between pectinase and lipase were observed,respectively.Moreover,synergistic effects on capillary rise height between?-amylase and pectinase,between?-amylase and lipase,between pectinase and lipase were observed,respectively.In supercritical CO2 fluids,?-amylase has a certain decomposition effect on starch on the fabric and can be used for desizing cotton fabrics.Supercritical CO2 fluid's pressure will have some effects on?-amylase's activity.The optimum process of?-amylase desizing is that the treatment time was 60 min,the treatment temperature was 70?,the supercritical CO2 fluid pressure was 12MPa,the concentration of?-amylase?2000u/g?was 0.021g/ml,the AOT concentration was 0.012 g/ml,the buffer?p H=6.02?was 40ml,and the ethanol was 10 ml.The kinetics of the desizing of the cotton fabric follows the law of the Michaelis-Menten equation.The kinetic model of the desizing process and the results show that the maximal reaction rate of Vmax was 0.00079 mg/?m L·min?,Michaelis constant of Km was 0.30790 mg/mL,and the kinetics equation of the desizing of?-amylase on cotton fabric in supercritical CO2 fluid could be shown as V=?0.00079?[S]?/?0.30790+[S]?,and the[S]is the substrate concentration for the enzymatic reaction.The polarity of supercritical CO2 fluid can be adjusted to a certain extent by an addition of water,so that some polar molecules can be dissolved in the modified fluid.The moisture content of supercritical CO₂ fluid,time,pressure and temperature have a certain effect on the cleaning of cotton fabrics which were desizd proviously.An optimized process for cleaning cotton fabric after being desized in supercritical CO₂ fluid was recommended as:water of 20ml,treatment time of 80min,pressure and temperature at16MPa and 110?,respectively.The?-amylase in supercritical CO₂ fluid has a great effect on the sized cotton fabrics with starch,and the desizing efficiency is remarkable.The cleaning process in supercritical CO₂ fluid can effectively remove the residues on the surface of the cotton substrate,which were produced from the decomposition of starch by?-amylase.Besides,there is little change of the structures of cotton fiber after enzymatic desizing and cleaning in supercritical CO₂ fluid.