| Traditional peroxide bleaching of cotton fabric requires a lot of chemical substances.After that,it needs a lot of water to wash off the residual chemicals,resulting in a large amount of effluent.Meanwhile,it will cause damage and strength loss to cotton fabric after long time and high temperature treatment.Therefore,researchers try to find an environment-friendly bleaching method that can replace the traditional process without losing the whiteness and quality standards of fabric.Ozone,as a new type of bleaching agent,has been widely applied in pulp bleaching due to its high oxidation potential(2.07 V),less water consumption and no harmful by-products in the reaction,which makes it possible for ozone bleaching of cotton fabrics with low pollution and low energy consumption.In this paper,firstly the effect of ozone bleaching time,pH,water pick-up value and concentration of oxygen in the bleaching conditions of cotton fabric was studied to obtain the optimal process:under room temperature,cotton fabric was padded 1.0 g/L wetting agent solution(pH 7)to gain water-pick value(W.P.V.)of 60%and treated with 30 min in the ozone atmosphere.After bleaching,cototn fabrics were cleaned with reduction solution,hot water,cold water and finally dried to inhibit the yellowing of fabric.Therefore,cotton fabric reached whiteness of 62,wetting time of 2.2 s,strength loss of 14%and desizing grade of 5;desizing of cotton fabric reached whiteness of 73,strength loss of 17%and removal rate of 52%to seed coat fragment(SCF);scouring of cotton fabric reached the maximum whiteness of 81,strength loss of 20%and removal rate of 89%to SCF.Then,ozone bleaching of cotton knitted fabric was studied.The results revealed that cotton knitted fabrics,which were impregnated with 1.0 g/L wetting agent solution and then bleached with 20 min in the ozone atmosphere,reached whiteness of 73,less strength loss of17%,wetting time of 1.3s under water-pick value(W.P.V.)80%and pH of 7 for 20 min treatment time.By determining the impurity content of fabric after ozonation,it was found that SCF,cotton wax and pectin decreased more than 88%,72%and 69%,respectively.On the basis of the above research to explore the mechanism of ozone bleaching on the removalof SCF,slice of seed coat faragment was firstly prepared to observe the structure of SCF by optical microscope.Then,each layer of micro infrared scanning of slice structure of SCF was obtained with infrared microscope.The chemical composition identified of SCF was utilized with the fast pyrolysis apparatus cracking.Finally,lignin isolated from SCF was characterized by gel permeation chromatography(GPC),nuclear magnetic resonance spectrum(~1H NMR)and Fourier transform infrared(FT-IR)spectroscopy and pyrolysis gas chromatography/mass spectrometry(Py-GC/MS)to analyse the structure changes of lignin before and after treatment with ozone.The results showed that molecular weight of the lignin reduced by 8%and methoxy content reduced by 1.31%,with obvious demethoxy reaction after ozone treatment.The phenolic hydroxyl was oxidized by ozone and participated in the ring opening reaction of benzene ring.The lignin of phenol type structure was broken with decreasing of connection structure of?-O-4 and?-?and decreasing of connection structure of?-1 and?-5.The results of Py-GC/MS suggested that the control and ozonated sample released products mainly from guaiacylpropanoid units,with the p-hydroxyphenyl/guaiacyl/syringyl composition changing from 4:53:43 to 3:58:39,with reducing of syringyl unit and basically unchanged on hydroxyl phenyl content. |
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