The Machanism And Process Of Dyeing Cationic Cotton With Reactive Dyes Without Alkali

Reactive dye is the main dye of cotton and other cellulose fiber.When cotton is dyed by reactive dyes,the main problems are appeared such as low utilization rate of dye,high consumption of electrolyte,difficult wastewater treatment and so on.In order to solve these problems,in addition to dyes' improvements,cationic cotton(cellulose)fiber is a more direct and effective method.At present,salt-free dyeing of cationic cotton has been recognized,but we have vague understanding to non-alkali dyeing.It has been considered that the washing fastness of shallow colors can be comparable with conventional dyeing.Non-alkali dyeing can make an excellent blank-leaving for unmodified cotton in a differential dyeing process,meanwhile it may be in favour of reducing hydrolyzed dyes.In this thesis,kniting cotton fabric made by CR-2000 modified cotton fiber supplied by an enterprise is mainly dyed with vinyl sulfone reactive dyes such as C.I.Reactive Red 180 and C.I.Reactive Blue 19,in order to know the theory of non-alkali dyeing,especially the fixation.Research on process conditions is done at the same time.At first Zeta potential of the surface of cationic cotton and ordinary cotton are tested.And the cationic cotton is tested under different p H values.Cationic cotton and ordinary cotton are dyed by reactive dyes and their hydrolysed dyes respectively with different dyeing processes.The before-soaping and after-soaping samples are stripped by 25% pyridine-oxalic acid solution.The kinds of bonds between cationic cotton and reactive dyes are speculated.It is found that the vinyl sulfone reactive dye Reactive Red 180 may have a fixation in the soaping stage when dyeing the cationic cotton without alkali.Further experiments are designed to confirm this imagine.On the basis of these results,one bath process without soaping is explored.At the same time,processing parameters of soaping such as time,p H value and soaping agent are studied.The way to search the best fit amount of dyes in non-alkali dyeing process is also conducted.The results of the experiments show that reactive dyes go into cationic cotton by electrostatic attraction.In the soaping stage,vinyl sulfone reactive dyes can be linked to cationic cotton by covalent binding with the help of feeble alkaline of the soaping liquor.Beta-hydroxy vinylsulfone-sulfate group,the precursor of the vinyl sulfone group,undergose an elimination reaction in the dyeing stage.It leads to a relatively low p H value in the dyeing bath so that satisfactory fixation is difficult to receive if the temperature of the dyeing bath is just raised.It is recognized that soaping is of great importance for fixation of dyes in the dyeing process without alkali.The suitable soaping condition can be like that raising the temperature to 95? at the rate of 2?/min and then maintaining for 20 min.By comparing the color yield and washing fastness obtained from dyeing process of cationic cotton with or without alkali,the suitbale amount of dyes for dyeing cationic cotton without alkali can be suggested.For Reactive Red 180 it is 2%(omf),and for Reactive Blue 191%(omf).At the end of dyeing,very small amount of alkali is added and the temperature is raised to simulate the bath replacing stage which can provide feeble alkaline.When compared with the dyeing-soaping two-bath process,the mechanism of non-alkali dyeing is clear and accordingly one bath dyeing process of cationic cotton with vinyl sulfone reactive dyes without soaping stage is explored.The process may be raising the temperature to 60? at the rate of 1?/min,maintaining for 45 min,and then adding sodium carbonate(0.3 — 0.7g/L)and raising the temperature to 95? maintaining for 20 min.Combining with industrial technique some experimental phenomena are explained or speculated,and some directions for extending research are also suggested.