| Because of their advantages such as complete chromatography and good color fastness,reactive dyes have been widely used in the field of dyeing and finishing.But the chemical additives,such as salt and alkali,are added to the dyeing and finishing process,and the dyes are easy to hydrolyze.It is difficult to deal with the waste water derived from the dyeing and endanger the environment.At the same time,the utilization rate and fixation rate of reactive dyes are low,and it is easy to cause waste.In order to achieve energy saving and emission reduction and improve the efficiency of dyeing,we designed and developed a device based on negative pressure dyeing,and constructed a dyeing technology based on negative pressure.The dyeing process was optimized by single factor experiment,and the mechanism and dyeing kinetics of negative pressure dyeing were explored and studied.The dyeing properties,such as lifting force,dye-uptake rate,fixation rate and K/S value,were compared with conventional dyeing.Firstly,the difference of evaporation capacity and evaporation rate of wet fabrics under negative pressure and atmospheric pressure is compared and analyzed in this paper.We have done the thermodynamic analysis of TG and DTG.The results show that the evaporation capacity and evaporation rate of water on the surface of fiber under negative pressure is better.The concentration gradient of the dye in the fiber surface and the inner layer is increased by it.It is beneficial to the diffusion of dye molecules attached to the surface of the fiber into the inner layer of the fiber.Secondly,C.I.Reactive Blue 19 and C.I.Reactive red 195 were used for negative pressure dyeing of cotton woven fabric and hemp knitted fabric.The dyeing properties and indexes of negative pressure dyeing and conventional dyeing are compared.The results show that,if the dye-uptake is the same,the amount of dyes and the amount of salt and the amount of alkali under negative pressure dyeing is less than the conventional dyeing.The amount of dye can be saved by 15%,the amount of salt can be saved by 10%,and the amount of alkali can be 15%.There is almost no white spot in the weft yarn interweaving of the fabric.The color of the yarn is deep and uniform.The yarn after twisting is uniformly colored from inside and outside,and there is no white core phenomenon.Thirdly,we studied the dyeing kinetics of negative pressure dyeing.The semi dyeing time(t1/2),the specific dyeing rate constant(K?)and the apparent diffusion coefficient(D)of the fabric were compared and analyzed.The results show that the dyeing rate of negative pressure dyeing is higher than that of the conventional dyeing.The diffusion kinetic energy of dye molecules under negative pressure dyeing is stronger than that under conventional dyeing.It is beneficial to the uniform dyeing of the fabric and increase the dye-uptake.Finally,we have optimized the experimental process.By evaluating the dye-uptake rate and fixation rate,K/S value and S value,to analyze the degree of vacuum,fixation temperature,self-made device running period,salt concentration and alkali concentration on the effect of fabric dyeing performance.We continue to study the Pre-alkali process on the basis of negative pressure dyeing.The results show that when the vacuum degree is-0.06 MPa,the operation cycle of the self-made device is 40 s,the concentration of salt is 40g/L,and the alkali concentration is 15g/L,the dyeing performance is the best.The best fixation temperature is different for different types of reactive dyes.The use of Pre-alkali process can avoid the decrease of the fixation rate and increase the reaction time.The Pre-alkali process makes the fixation rate slow,and improves the level-dyeing property.Negative pressure dyeing is a competitive and promising dyeing technology,no matter from saving dye dosage,reducing the dosage of salt agent,alkali agent,or decreasing dyeing pollutants and sewage discharge.It has the significance of the sustainable development of dyeing and finishing and the production of energy saving and environmental protection. |
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