Optimization Of Pretreatment Process For Cotton Knitted Fabric

Cotton knitted fabric needs to be pretreated before dyeing,in order to remove the natural impurities for good whiteness and hygroscopicity.The conventional pretreatment process needs higher temperature and alkali conditions,the COD value of residual liquid is high,and the treated fabrics has to be carried out respectively by acid neutralization,deoxygenation and washing,which consume a large amount of energy and water.Therefore,the main research now focus on the energy saving and pollution reduction technology in textile printing and dyeing industry.It is an inevitable trend to develop an environment-friendly pretreatment process for cotton fabric,which is of great significance for sustainable development.At the same time,dyeing is also an important processing for cotton knitted fabric.It is of great significance to study the dyeing performances of fabrics treated by different pretreating processes for practical application.In this paper,the four pretreatment processes,that are Tea Saponin process,one-bath two-step process of enzymatic scouring and oxygen bleaching,low temperature activation and low alkali catalysis processes were optimized,compared with conventional alkali scouring and oxygen bleaching process used for cotton knitted fabric.were.From the two indexes of whiteness and capillary efficiency,the influence of different factors on the treatment effect of each process was discussed,and the optimum prescription and process was obtained.Among them,the pretreatment performances of low alkali catalysis and Tea Saponin process is better.The optimum conditions of low alkali catalysis process is as follows:Super BLUE 1g/L,NaOH 1.1g/L,H₂O₂ 7g/L,temperature98°C,time 45min,the processing flow is:scouring and bleaching?deoxidize?washing,the whiteness of the treated fabric is 75.24,capillary effect value is 17.2cm,bursting strength is 80.8psi;the optimum condition of Tea Saponin process is as follows:penetrant AP800 0.8g/L,Tea Saponin HD-190 7g/L,98°C,50min,the processing flow is:Tea Saponin scouring and bleaching?acid neutralization?deoxidize?washing,the whiteness of the treated fabric is 75.65,capillary effect value is 14.6cm,bursting strength is 88.8psi.Secondly,the influence of pretreatment residual liquid on the environment was studied.By detecting the COD value of residual liquid of different pretreatment processes,the results that the COD value of residual liquid of the one-bath two-step process of enzymatic scouring and oxygen bleaching was the lowest,at 1862mg/L,which can reduce environmental pollution;the low temperature activation process was the highest,at 4761mg/L,which increased the difficulty of sewage treatment.COD values of the other three processes is between 2100mg/L and 2500mg/L,among which the components of scouring agent in the residual liquid of Tea Saponin process can be biodegraded,which has relatively little impact on the environment.Then,the differences of dyeing performances of fabrics pretreated by different processes were studied.The reactive dyes with one or two reactive groups were applied for dyeing the fabrics after pretreatment,and the dye uptake,fixation,soaping fastness and rubbing fastness were tested.The results show that the dye structure is the main factor affecting its dyeing performance,and the dye uptake and fixation of the fabric pretreated with one-bath two-step process of enzymatic scouring and oxygen bleaching are slightly reduced.For the dark dyeing of reactive dyes,one-bath two-step process of enzymatic scouring and reactive dyeing was used for cotton fabric.The results show that the dyeing depth and fastness of this process were basically the same as those of the traditional process,which could meet the dyeing quality requirements for dark color.Finally,the low alkali catalysis bleaching process and one-bath two-step process of enzymatic scouring and reactive dyeing were applied in the dyeing factory.The results show that both processes can achieve similar dyeing results comparing with the traditional process.The low alkali catalytic process can save 21%of the auxiliary cost,25%of the water saving and 12%of the production time.one-bath two-step process of enzymatic scouring and reactive dyeing saves 75%of water and 65.2%of production time,which has better economic and environmental benefits and application prospects.