Study On Dyeing Properties And Mechanism Of Cotton Fabric With Reactive Dyes In Non-aqueous Media

Conventional water bath dyeing of cotton fabrics with reactive dyes shows some problems such as low dye utilization rate,large amount of neutral salt needed,high water consumption and heavy burden of wastewater treatment.With the increase in environmental and energy pressures,it is urgent to develop a new clean dyeing technology for reactive dyeing.In recent years,D5(decamethylcyclopentasiloxane)non-aqueous dyeing technology of reactive dyes has attracted wide attention in academia and industry due to its advantages of salt-free and water-saving.However,D5 has recently been listed as a substance of high concern by the European Union,and there are certain risks in its development and application.The reactive dye/liquid paraffin dyeing process developed by our research group in the early stage has various advantages which D5 nonaqueous dyeing showed,and it is a friendly process to human body and environment.However,non-aqueous dyeing shows the problem of uneven dyeing,which limits the development and application of this technology to a certain extent.Aiming at the unevenness of non-aqueous dyeing of cotton fabrics with reactive dyes,this article mainly conducts the following three aspects of research work:(1)Abrasive modification of reactive dyes.The effects of surfactant,ball milling time and size of zirconia beading on the dispersion properties of three dyes(reactive red 195,reactive yellow 176 and reactive blue 194)in non-aqueous media were studied.The surfactant and the grinding process of color paste were optimized,and the mechanism of surfactant was studied.(2)Explore the key stages of dyeing unevenness and optimize the dyeing process.The key dyeing stages of unevenness were identified,and then the effects of dyeing temperature and time,type and concentration of alkali agent,fixation temperature and time on dyeing properties such as evenness and color yield were studied.The dyeing process was optimized,and the pilot test was carried out.(3)Research on dyeing theory.The properties of dye dissolution,aggregation and charge in different media and the properties of fiber swelling and Zeta potential which are closely related to reactive dye dyeing were studied.The thermodynamic and kinetic properties of dyeing cotton with reactive dyes in different media were further studied.The results showed that:(1)The optimal preparation process of high concentration reactive dye paste was adding dispersant GA in D5 media and dispersant LK in liquid paraffin media.The diameter of zirconia bead was 1-2 mm and the grinding time was 5 h.The structure of the surfactant is characterized by an aromatic ring structure at one end and a hydrocarbon chain structure at the other end.(2)Strategies to improve evenness: a)Pre-swelling the fabric sufficiently before dyeing;b)Dyeing at low temperature and extending the transfer time;c)Add alkali in the later stage,and add alkali agent to fix the dye after ensuring uniform dye transfer.The optimal dyeing process in non-aqueous media was as follows: The dyeing temperature was 30 ?,the dyeing time was 30 min,the concentration of sodium carbonate was 90 g/L,the fixing temperature was 80 ?,the fixing time was 40 min.The color light of the dyed fabrics were pure,and the color fastness to rubbing and soaping were the same as that of the conventional water bath dyeing.The color yield of 1 kg yarn in the pilot test was higher than that in the conventional water bath,and the evenness was good.(3)The properties of cotton fibers and reactive dyes in different media were as follows:the swelling rate of cotton fibers in different media was in the order of Water>DMSO>D5>Liquid paraffin,indicating the necessity of sufficient pre-swelling of fabric before dyeing in non-aqueous media.The charge of cotton fiber and reactive dye in water was negative,but the charge of cotton fiber and reactive dye in non-aqueous media was almost zero,which explains the reason why salt cannot be completely used in non-aqueous media.Reactive dye was almost insoluble in D5 and liquid paraffin media,and easy to aggregate.It is suggested that mechanical stirring and appropriate surfactants should be used to ensure the uniformity of the dyeing system and the color uniformity of the final dyed fabric than that of conventional water bath dyeing;(4)The kinetic and thermodynamic characteristics of cotton dyeing with reactive dyes in different non-aqueous media were as follows: the dyeing of cotton with reactive dyes in water,D5 and liquid paraffin media conformed to the quasi-second-order kinetic model;In water,D5 and liquid paraffin media,the adsorption isotherm conformed to Freundlich type,which belongs to multi-molecular layer physical adsorption.The affinity in water,D5 and liquid paraffin media was positive,and the affinity in non-aqueous media was much higher than that in water bath.The higher the chemical potential of reactive dyes in dye solution,the higher the dyeing affinity.In D5 and liquid paraffin media,the dyeing entropy was positive,which was mainly attributed to the decrease of hydrophobic self-polymerizing structure between non-aqueous molecules and the ice-like structure between water molecules,and the increase of system disorder.The dyeing heat of nonaqueous media was positive,indicating that the dyeing process was endothermic,which was mainly due to the “melt endothermic” of the ice-like structure between water molecules and the“depolymeric endothermic” of the hydrophobic self-polymeric structure between non-aqueous media molecules.These properties were of guiding significance for understanding and interpreting the dyeing properties and behavior of cotton fabrics dyed with reactive dyes in non-aqueous media.