Study On The Principles Of Dyeing Technology With New Non-aqueous Media

With the increased emphasis on clean production and sustainable development in dyeing and finishing industry,the non-aqueous medium dyeing technology has attracted more and more attentions.However,the research on non-aqueous medium dyeing theory and principles lags behind the development of dyeing technology,and some special phenomena appeared in non-aqueous medium dyeing and their intrinsic causes have not been fully explained and generally accepted.In order to improve and deepen the research of non-aqueous medium dyeing theory and promote the development of non-aqueous medium dyeing technology,this subject took non-polar media of decamethylcyclopentasiloxane(D5)and liquid paraffin(LP)as the main research objects,and compared with the polar medium of dimethyl sulfoxide(DMSO)and the conventional medium of water.The swelling property,Zeta potential and supramolecular structure of fibers in non-aqueous media,as well as the solubility,aggregation state and charge property of dyes,which are closely related to dyeing,were studied from multiple angles and levels.The dyeing process and dyeing properties of cotton dyed with reactive dyes and polyester dyed with disperse dyes in non-aqueous medium system were discussed,and the dyeing thermodynamic properties(adsorption isotherm,dyeing affinity,dyeing heat and dyeing entropy)and dyeing kinetic properties(dyeing rate curves,dyeing rate constants,apparent diffusion coefficients and diffusion activation energy)were focused.The molecular dynamics simulation model of cotton dyeing with reactive dyes and polyester dyeing with disperse dyes in non-aqueous medium system was constructed,and the process and degree of fiber dyeing with dyes in non-aqueous medium system were further explored from the perspective of computational chemistry.The main research conclusions are as follows:(1)The swelling properties of fibers are different in different media.The influence of the medium on the swelling degree of cotton fibers is in descending order:water>DMSO>D5≈LP.The stronger the polarity and the smaller the size of the medium molecules,the stronger the swelling ability of cotton fibers.Both D5 with cyclic symmetry structure and LP with linear alkane structure are nonpolar media,which basically has no swelling effect on cotton fiber.The structure of polyester fiber is compact,and the medium has little effect on its swelling degree.The relative order of medium effect is DMSO>LP≈water≈D5.In view of the low swelling of cotton fiber in new non-aqueous medium(D5 and LP),a strategy of fully pre swelling cotton fabric before dyeing is proposed to ensure that cotton fiber has sufficient dye accessibility and diffusion channel in new non-aqueous medium dyeing,which is conducive to improving dye penetration and levelness.The Zeta potential of cotton fiber and polyester fiber in non-aqueous medium(D5 and LP)is close to zero.Cotton fibers and polyester fibers were immersed in non-aqueous medium at 70°C and 125°C for 1 h,respectively,and their molecular structures did not change significantly.(2)The solubility,aggregation state and charging properties of dyes in different media are different.Reactive dyes are almost completely insoluble in new non-aqueous media(D5 and LP),resulting in strong interfacial energy between reactive dyes and new non-aqueous media.There is no electrostatic repulsion between reactive dyes(droplets)and cotton fibers containing water in the new non-aqueous medium,which explains the basic reason why the new non-aqueous medium dyeing of cotton with reactive dyes can realize salt-free dyeing.The insolubility,easy aggregation and fast adsorption of reactive dyes in new non-aqueous media bring the negative problem of easy dyeing unevenness.Disperse dyes have a certain solubility(greater than that of disperse dyes in water)in new non-aqueous media(D5 and LP),and it increases significantly with the increase of temperature.The better solubility of disperse dyes in the new non-aqueous medium alleviates the uneven dyeing phenomenon caused by dye aggregation,and this effect is more obvious when the temperature increases.However,this increases the distribution ratio of disperse dyes in the new non-aqueous medium,resulting in lower dye uptake.(3)The dyeing process and fixing process curves of reactive dyes in non-aqueous medium suspension method and micro-aqueous system method are significantly different from those in conventional water bath dyeing.In the first few minutes of the low temperature stage of dyeing,reactive dyes quickly adsorbed dyed cotton fibers and reached nearly 100%dye uptake,mainly due to the absence of electrostatic repulsion between dyes and fibers and the driving force of high interfacial energy between dyes and media.At the same time,in the low temperature stage of dyeing,the total fixation rate of reactive dyes has reached more than 15%,which is attributed to the ultra-small liquor ratio alkaline environment formed by padding alkali solution before fiber dyeing,which provides the conditions for the reaction between dyes and fibers,so that the dye can rapidly covalently bond with the cotton fiber negative ions in the accessible area on the fiber surface and near the surface.It is clear that the low-temperature initial dyeing stage is the key stage to cause the uneven dyeing of reactive dyes in non-aqueous media.Then,from the perspective of dyeing process control,a series of strategies to improve the levelness are put forward,and an effective method for rapid and uniform dyeing of reactive dyes in new non-aqueous media is established.The dyeing process of disperse dyes in the new non-aqueous medium micro water system can be divided into three obvious stages:adsorption stage(low temperature stage,the dye is mainly adsorbed on the fiber surface),desorption stage(increasing the temperature to T_g,the dye is mainly desorbed from the fiber surface)and fixation stage(the temperature is above T_g,the dye diffuses from the fiber surface to the inside,and then fixation).Adding a small amount of water to the non-aqueous medium as an auxiliary agent for plasticizing fibers and promoting dyeing is beneficial to reduce the glass transition temperature of polyester fibers and repel(promote)the dye abandonment medium to adsorb on the fibers and improve the dye uptake.(4)The adsorption isotherms of cotton fabrics dyed with reactive dyes in water and new non-aqueous media(D5 and LP)accord with Freundlich isotherm equation,which belongs to multi-molecular layer physical adsorption.The strong interface energy between reactive dye droplets and the new non-aqueous medium can lead to the dyeing affinity for cotton fiber in the new non-aqueous medium system is greater than that in the aqueous medium.In the reactive dye non-aqueous medium dyeing system,the ice like structure of water molecules and the hydrophobic aggregates of non-aqueous molecules increase the dyeing entropy and dyeing heat of the system through“melting endothermic”and“depolymerization endothermic”in the dyeing process,so that they are positive,contrary to the dyeing results in conventional aqueous medium.The dyeing rate constant and apparent diffusion coefficient indicate that reactive dyes can reach the dyeing equilibrium faster in the new non-aqueous medium system.The lower diffusion activation energy than that in aqueous medium shows that the new non-aqueous medium system is more conducive to dyeing cotton fabric with reactive dyes.The adsorption isotherms of polyester fabric dyed with disperse dyes in aqueous medium and new non-aqueous medium accord with Nernst isotherm equation,and the distribution ratio of dyes between fiber and dyeing bath is constant.The dyeing affinity of disperse dyes in the new non-aqueous medium is lower than that in water,because the solubility of disperse dyes in the new non-aqueous medium is higher than that in water,which increases the distribution ratio of the dye in the new non-aqueous medium.The dyeing heat,dyeing entropy,dyeing rate constant and apparent diffusion coefficient of disperse dyes in new non-aqueous medium have the same sign and change trend as those in aqueous medium.The diffusion activation energy of disperse dyes in the new non-aqueous medium is higher than that in the aqueous medium,indicating that the solubility of disperse dyes in the new non-aqueous medium hinders the dyeing to a certain extent.(5)The molecular dynamics simulation system of dye dyed fiber implemented by Gromacs software package simulates the adsorption process of reactive dyes and disperse dyes on cellulose fiber and polyester fiber in water bath and LP bath from the atomic level.Based on this,the characteristic parameters of dyes in different simulation systems,such as mean square displacement(MSD),Z-direction number density,interaction(van der Waals interaction,Coulomb interaction),hydrogen bond and XY plane number density,are compared.The results show that the chemical potential of reactive dyes in LP system is higher than that in water bath,so reactive dyes can dye cellulose fibers faster and more in LP system than in water bath.The MSD slope and number density of disperse dyes dyeing polyester fiber in LP system are lower than those in water bath,indicating that the dye uptake and dyeing rate of disperse dyes in LP system are lower than those in water bath,which proves that the solubility of LP to disperse dyes is not conducive to disperse dyes dyeing polyester fiber.