| Conventional dyeing for textile is generally performed in water base.In such a process,waste aqueous effluent contains hydrolyzed dyes,inorganic salts,alkalis,and other chemicals such as surfactants etc.How to reduce or even avoid the using of water in reactive dyeing,control the using of toxic chemicals,reduce the dyeing effluents,and realize eco-friendly dyeing are the theme for the sustainable dyeing development.Non-aqueous dyeing is one of representative dyeing techniques which uses non-polar media to substitute the traditional water base.Non aqueous dyeing media can neither dissolve the water soluble dye nor water,but it can transport material and transfer energy.The dye,alkali agent and other dyeing auxiliaries are dissolved in a small amount of water which is dispersed or emulsified in non-polar media.Therefore,the study in this field has been an important aspect of dyeing research.In summary,reactive dye can achieve a higher dye uptake(close to 100%)and a higher fixation rate than that in the traditional water base dyeing.However,the reason is not studied systematically.In order to studied the dyeing mechanism of reactive dye for cotton fabric in siloxane non-aqueous dyeing system.Decamethyl cyclopentasiloxane(D5),which is a safe and environment-friendly chemical,is selected as the continuous phase.Because of the reactive dyeing in siloxane medium is an unique innovation system,the adsorption of dye and the fixation mechanism between fiber and dye in traditional water base can not be applied in siloxane non-aqueous dyeing system.It need to build a new dyeing mechanism which is suitable for textile dyeing in siloxane non-aqueous medium.As a result,the distribution of D5/water in siloxane dyeing system,the adsorption and fixation mechanism of reactive dye on cotton fabric are investigated in this paper.Those important technical issues are as follows:1.Adsorption mechanism of reactive dye for cotton fabric in siloxane non-aqueous dyeing systemTo study the adsorption mechanism of reactive dye for cotton fabric in siloxane non-aqueous dyeing system,amount of non-aqueous dyeing media with different surface tension are chosen.By complex formulation,the effect of non-aqueous dyeing media with different surface tension on the dyeing rate and finial up-take of reactive dyes are studied.Dyeing kinetics of reactive dye in siloxane non-aqueous dyeing system and traditional water base system is compared via a pseudo-first-order kinetic model and a pseudo-second-order kinetic model.The results show that the adsorption behavior of reactive dye for cotton fabric obeys the pseudo-second-order kinetic model for both non-aqueous media and traditional water bath system.In the siloxane non-aqueous dyeing system,reactive dye would quickly diffuse into fabric surface because of the affinity between fiber and reactive dye is higher than that of the non-aqueous dyeing media.Research shows that:(1)In the non-aqueous dyeing system,the surface tension of dyeing media is the main factor which affects the adsorption rate of reactive dye.The lower the surface tension,the faster is the adsorption rate of reactive dye for cotton fabric in non-aqueous dyeing system.(2)In the siloxane dyeing system,the adsorption rate of reactive dye for cotton fabric is much faster than that in traditional water base(three to seven times).(3)In the non-aqueous dyeing system,the final uptake of reactive dyes for cotton fabric(close to 100%)is higher than that of the traditional water bath dyeing(60-70%).(4)In the siloxane dyeing system,the adsorption rate of reactive dye for cotton fabric in siloxane suspension system is five to six times faster than that in siloxane micro-emulsion system.The main reason is that the emulsification of surfactant increases the stable of reactive dye solution in siloxane dyeing system,thereby reducing the adsorption rate of reactive dye to the fabric surface.(5)In the siloxane non-aqueous dyeing system,the final uptake of reactive dye keeps stable with the temperature increase but it significantly decrease in the traditional water bath.The main reason is that the solubility of reactive dye in aqueous solution increases with the temperature increasing.2.Hydrolysis mechanism of reactive dye in siloxane micro-emulsion dyeing systemA major advantage of dyeing cotton fabric in siloxane medium is just need a little water,which might influence the hydrolysis of reactive dye.The hydrolysis mechanism of reactive dye under different conditions is studied using a HPLC(high performance liquid chromatography)analysis in the siloxane dyeing system and traditional water base.Impacting factors on the hydrolysis of reactive dye from surfactant,co-surfactant,dye concentration,cotton fabric addition as well as the dyeing temperature are systematically studied.The results show that the hydrolysis of reactive dye in siloxane dyeing system is slower than that in traditional water bath.The hydrolysis rate of reactive dye in siloxane dyeing system is about quarter to one third.The main reasons for reactive dye hydrolysis mechanism in siloxane dyeing system are as follows:(1)Dyeing rate.In the silicone micro-emulsion dyeing system,reactive dye can be rapidly diffused into cotton fabric,reducing the time of reactive dye in the dye bath,thereby reducing the hydrolysis of reactive dye.(2)The amount of water.Compared with traditional water dyeing bath,a little water(130%,owf.)is used in the siloxane dyeing system.As a result,a high concentration of dye which is emulsified in siloxane media would reduce the average hydroxyl which is used in the hydrolysis of dye.Thereby,the hydrolysis of reactive dye can be effectively reduced.(3)Surfactant or co-surfactant.In the silicone micro-emulsion dyeing system,the water grasping ability of surfactant or co-surfactant might reduce the 'free-water'which is used in dye hydrolysis,thereby the hydrolysis of reactive dye can be effectively reduced.(4)Dyeing condition.Reactive dye are dispersed into small particles in the siloxane micro-emulsion dyeing system,and the hydrolysis of reactive dye might be weaken in the tiny particle environment,thereby,the hydrolysis of reactive dye can be effectively reduced.3.Bonding mechanism of reactive dye for cotton fabric in the siloxane micro-emulsion dyeing systemA higher fixation of reactive dye could be achieved in the siloxane non-aqueous dyeing system,reducing the loose color which adsorb on the fabric surface.As a result,the hydrolysis dye or unfixed dye would be decreased greatly.A high concentration of dye is formed on the fabric surface which is different from traditional water dyeing.So,the fixation rate and the changing of active groups or elements before and after dyeing will be investigated using different reactive dyes.The chemical environment of element will further be studied to analysis the bonding mechanism of reactive dye in siloxane dyeing system.The color depth of fabric and the fixation rate of dye in the silicone dyeing system are much higher than those in traditional aqueous system.From the X-ray photoelectron spectroscopy,the elements of cellulose fiber surface are changed after dyeing with reactive dye.For example,the content of N is gradually increased with the fixation time.Furthermore,compared with the control cellulose,the peak area of C-H or C-C is gradually increased after dyeing,but the peak area of C-O is decreased gradually.The main reason is that a large amount of reactive dye adsorb on the cellulose fiber surface after dyeing,and the chemical bond of C-C or C-H has a higher percentage in reactive dye molecular structure.As a result,the C1s chemical environment on the cellulose fiber surface will be changed after dyeing.Therefore,the bonding mechanism of reactive dye can be studied by the chemical environment of C1s in siloxane dyeing system.4.Swelling of fiber and distribution of D5/water in siloxane dyeing systemSwelling of fiber in siloxane dyeing system and traditional water base,and distribution of D5/water in fiber were investigated via fluorescent labeling.The results show that fiber could get a well swelling by the aqueous solution which was dispersed or emulsified in non-aqueous dyeing system.However,the fiber was difficult to swell by the non-aqueous media.In non-aqueous media dyeing system,non-aqueous dyeing media rapidly adsorb on the fiber surface,but it difficult to diffuse the inner of fiber in dyeing system.However,water molecule which was dispersed or emulsified in non-aqueous media could diffuse into the inner of fiber to swell the fiber.Water soluble dye could through siloxane film of fiber surface,and diffuse on fiber surface in siloxane non-aqueous dyeing system.Most remarkably,comparing with the fluorescent intensity,the siloxane film hardly washed with water soluble dye solution,while it can be re-transferred to the dye bath under the mechanical force and the emulsification of surfactant.As a result,reactive dye has an excellent level dyeing property in siloxane micro-emulsion dyeing system.In conclusion,compared with traditional water dyeing,not only reactive dyeing without using salt in siloxane micro-emulsion dyeing system can realize,but also the final up-take and fixation of reactive dye are up to 100%,90%,respectively.Furthermore,we study the reason why the hydrolysis of reactive dye in siloxane micro-emulsion system is lower than that in traditional water base and the influencing factors,which will provide a basic work for the reactive dyeing in silioxane non-aqueous dyeing system and industrial production. |
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