Structure-activity Relationship Between Lignin Dispersant And Nano Disperse Dye And Its Dispersion Mechanism

The process of traditional printing industry is complex,the waste water discharge is large,and the quality is low.Digital printing is a new type of printing technology.The printing process has a high dye uptake rate and no waste water.It conforms to the green chemistry production process,so it has developed rapidly in the past five years.Nano disperse dyes have the characteristics of small particle size and excellent stability,and can be used for inkjet printing of digital printing,so they are the main consumables for digital printing.Lignin dispersant has the characteristics of natural green and non-toxic,to meet the requirement that the additives of digital printing ink must be non-toxic and harmless,so it is widely dispersed in the field of nano disperse dyes.However,the work on dye dispersants at home and abroad is mainly focused on traditional micron disperse dyes to solving the key properties of lignin dispersants such as high temperature stability,reducibility,and adhesion,due to nano disperse dyes are an emerging industry.There is very little research work on lignin dispersants for nano disperse dyes.At present,engineers in this field use lignin dispersant for micron disperse dyes in nano disperse dyes,but there are disadvantages such as low sanding efficiency,high cost,and poor stability of nano disperse dyes.Starts with the structure of the lignin dispersant,this paper systematically studies the influence of the sulfonic acid group,carboxyl group and molecular weight of the lignin dispersant on its application performance in nano disperse dyes,reveals the structure-activity relationship,and explores the adsorption mechanism of different structures of lignin in nano-disperse dyes.The structural models of sulfonated lignin,carboxymethylated lignin and sodium polyetheramine-bridged lignin sulfonate with different group contents were designed,Molecular simulation software was used to analyze the adsorption of lignin dispersant on dyes by intermolecular force.And then made of alkali lignin（AL）,Using sodium sulfite as sulfonation reagent,sodium chloroacetate as carboxylic reagent,sulfonated lignin（SAL）with different sulfonic groups content and carboxymethylated lignin（CAL）with different carboxyl groups content were prepared,respectively.Use sodium lignosulfonate（SL）as raw material,polyetheramine-bridged lignin（PSL）with different molecular weight was prepared by using polyether amine（PEA-400）as bridging agent.A series of lignin dispersant samples（SAL,CAL,PSL）were characterized by FT-IR,NMR,EA,GPC and potentiometric titration,demonstrating the introduction of different amounts of sulfonic groups into SAL samples,Different carboxyl groups were introduced into CAL samples,A series of PSL samples with different molecular weights were prepared.A series of SAL,CAL,PSL with different structures were used as dispersants,nano disperse dyes were prepared by sanding in water-based systems.First,The effects of sanding time,dye-bead ratio,zirconium bead ratio of different diameters and dispersant dosage on the properties of nano disperse dyes were systematically studied,the optimum sanding process formulation was obtained as follows:dye is 20 wt.%,dispersant is 12 wt.%,dye-bead ratio is1:30（wt.%）,zirconium beads of different diameters（1 mm:0.5 mm:0.3 mm）ratio is 4:4:2（wt.%）,sanding time is 9 hours.According to the best sanding formula,nano disperse dyes was prepared with different lignin dispersants.Through the characterization of the particle size,stability and thermal storage stability of the nano disperse dyes,the dispersants with different group content in the series SAL,CAL,PSL dispersants were finally optimized as PSL₃（Mw=30770）,SAL_1.53（sulfonic group content is 1.53 mmol/g）,CAL_2.51（carboxyl group content is 2.51 mmol/g）.The minimum D₉₀size of nano disperse dyes prepared by PSL₃,SAL_1.53,CAL_2.51is 168 nm,173 nm,176 nm,respectively.All of the particle size is less than200 nm,the stability of the nano disperse dye is good after 7 days of thermal storage,still maintain low viscosity and uniform condition before and after thermal storage,comparable to the imported lignin dispersant Reax 85A.Quartz crystal microbalance,atomic force microscope and zeta potentiometer were used to study the adsorption properties of lignin dispersants with different structures on the surface of dyes.The results found that for PSL of different molecular weights,as the molecular weight of the lignin dispersant increases,the adsorption force between the dispersant and the dye first increases and then decreases,and the adsorption amount of the dispersant on the dye increases,the rigidity of the layer is increased and the desorption amount is reduced.Among them,the adsorption amount of PSL₃is the largest,the desorption amount is the smallest,and the absolute value of the zeta potential is the largest.For SAL with different sulfonic acid group content,the adsorption force between the dispersant and the dye gradually increases,the adsorption amount of the dispersant on the dye increases,the rigidity of the adsorption layer increases and the amount of desorption decreases as the content of sulfonic acid groups increases.Among them,the adsorption amount of SAL_1.53is the largest,the desorption amount is the smallest,and the absolute value of the zeta potential is the largest.For CAL with different carboxyl content,as the carboxyl content increases,the adsorption force between the dispersant and the dye first increases and then decreases,the adsorption amount of the dispersant on the dye first increases and then decreases,and the amount of desorption decrease first and then increase;the adsorption amount of CAL_2.51is the largest,the desorption amount is the smallest,and the absolute value of zeta potential is the largest.In summary,lignin dispersant with higher sulfonic acid group content,carboxyl group content and molecular weight are conducive to the adsorption of dispersant on the surface of the dye,which is conducive to increasing the absolute value of the zeta potential of the dye/water interface,and it is beneficial to improve the stability of the nano disperse dye system.The structure-activity relationship between the structural of lignin dispersant and the properties of nano disperse dyes is explored in this paper,and the dispersion mechanism and stability mechanism of nano disperse dye system are revealed.The research results can be used for the structural design of high performance lignin dispersants.