Pretreatment Processes Of Cotton Fabric With Hydrogen Peroxide Activated Systems

The pretreatment of cotton is one of the most important processes during dyeing and finishing procedures for textiles.The traditional pretreatment processes are often conducted under the high temperature with strong alkaline conditions,which cause a deep chromaticity and high COD value of wastewater and waste lots of energy and fresh water,bringing great burden on the environment.Therefore,energy conservation and emission reduction technology become an inevitable development trend of pretreatment.The activators can promote bleaching of fabrics with hydrogen peroxide（H₂O₂）at low temperature,which can effectively reduce the energy consumption.However,the bleaching mechanism of H₂O₂ activated systems has not been fully clarified.Three low-temperature activators were employed in this study: tetraacetyl ethylenediamine（TAED）,pent-acetyl Glucose（PAG）,a kind of commercial activator JML-2.Their effects on the bleaching performance were investigated in detail.At the same time,the method of fluorescence probe detection of hydroxyl radicals was employed to discuss the mechanism of H₂O₂ activated system.Polysaccharide PAG with good biodegradability was adopted in the low temperature activated bleaching（LTAB）of cotton,which has not been applied in textile industry.LTAB processes were often adopted in intermittent bleaching processes.We made a try to apply activator in stacking process instead of steaming process during bleaching woven fabrics,which could effectively reduce energy consumption and save industrial water during pretreatment.Firstly,the soaking process of LTAB was investigated.Three low-temperature activators,TAED,PAG and JML-2 were separately added into the bleaching bath,and by taking whiteness index as well as the decomposition rate of H₂O₂ as the main measurement parameter,the optimum condition was selected out: 30% H₂O₂ 5 g/L,Na OH 2 g/L,PAG or TAED or JML-2 3 g/L,bleaching at 70℃ for 60 min.Secondly,the bleaching mechanism of H₂O₂ activated system with different activators was discussed.The hydroxyl radical（OH·）in TAED/H₂O₂,PAG/H₂O₂ and JML-2/H₂O₂ systems wasdetected with a novel fluorescent probe benzenepentacarboxylic acid（BA）.The results showed that OH· yield in TAED/H₂O₂ and PAG/H₂O₂ systems were 9 times and 7 times higher than that in H₂O₂ system at the same p H,while it was not increased in JML-2/H₂O₂ system.Taking the influence of OH· on whiteness and strength of treated fabrics into consideration,it proved that OH· played a significant role in TAED/H₂O₂ and PAG/H₂O₂ systems.While in JML-2/H₂O₂ bleaching system,OH· had little effect on promoting bleaching performance.Finally,an improved pretreatment process,medium temperature stacking process,of cotton fabrics was tried.Activators were applied in the long-continuous process of woven fabrics according to its bleaching performance at lower temperature.Complex enzyme cold pad-batch/H₂O₂ activator medium temperature stacking pretreatment process was developed.On the basis of enzyme desizing rate and residual rate of pectin of the treated fabrics,the complex enzyme cold pad-batch process was optimized: complex enzyme HD-100 6 g/L,MP-2 2 g/L,cold pad-batch time 10 h,and p H 7-8.Cotton pretreated with complex enzyme was directly padded with H₂O₂ activated bleaching solution without washing process.The washing-free process can effectively save water consumption and reduce the processing steps.The processes of H₂O₂ activator bleaching at medium temperature pad-batch were conducted by orthogonal experiment and single-factor experiment.The optimum process conditions are: 100% H₂O₂ 15 g/L,JML-2 3 g/L,stacking at 85℃ for 90-100 min.The whiteness of fabric treated under the optimum conditions can reach 75.42 and the strength was about 5% higher than that of fabric treated under the traditional steam processes.The stacking process was carried out at a medium temperature（85℃）instead of one as high as 100℃ in the traditional steam process,which would effectively save the energy and would meet the requirements of energy conservation and emissions reduction during the pretreatment of cotton fabrics.