Study On Preparation Of Lignosulfonate Waterborne Epoxy Resin Dispersant Based On Ternary DES

With the destruction of the ecological environment and the strengthening of environmental protection,the green and water-based epoxy resin system is increasingly favored by researchers at home and abroad.In this paper,a self-made choline ternary DES was used to catalyze and activate the sodium lignosulfonate（LS）,and then the treated sodium lignosulfonate（TLS）was separated and modified with epoxy resin to prepare a lignosulfonate-based waterborne epoxy resin dispersant.And by means of phase inversion emulsification accompany with ultrasonic assisted dispersion,a stable waterborne epoxy resin emulsion product is obtained.In this process,the single-factor control variable method was used to screen out the optimum condition of preparing ternary DES,ternary DES catalyzing and activating LS and the preparation of waterborne epoxy resin emulsion.Finally,the epoxy resin emulsion prepared by the optimal process and the polyether amine curing agent are used to form a waterborne epoxy coating.The performance of the cured varnish film is tested and analyzed,and the curing mechanism of the waterborne epoxy coating is preliminarily analyzed.The main conclusions of this study are as follows:（1）Taking choline chloride as a hydrogen bond acceptor and urea,malonic acid and glycerol as hydrogen bond donors,the optimal molar ratio of the ternary DES system is 1:1:1,and the viscosity of the ternary DES is relatively lowest.Among them,choline chloride/urea/glycerol DES has too high viscosity at room temperature,which is not conducive to operation.From the TG analysis,the thermal stability of choline chloride/urea/malonic acid DES was better than that of the choline chloride/malonate/glycerol DES system under the same molar ratio.The final screening of the ternary DES system is choline chloride/urea/malonic acid DES（1:1:1）,and it has excellent flow and good thermal stability,which contribute to the degradation and activation of LS.（2）After treatment by choline chloride/urea/malonic acid DES,the weight-average molar mass of TLS is reduced,the molecular weight distribution is narrowed,and the surface activity is improved,but when the temperature is too high,Small molecules of lignin that may cause degradation polymerize.It can be seen from the FTIR that the modification treatment of ternary DES does not destroy the activity of sulfonic acid groups at 1040 cm^-1 and 652 cm^-1.The additions of the in-plane bending vibration absorption peak at 952 cm^-1 and the-0-H out-of-plane bending vibration absorption peak in the carboxyl group at 1367 cm^-1 which indicate the activity of the surface hydroxyl groups improving.Comprehensive analysis,the optimum condition for catalyzing and activating LS by choline chloride/urea/malonic acid DES is as follows:treatment temperature 100°C,treatment time 4h,solid-liquid ratio 1:10.（3）The solid content affects the stability of the emulsion by affecting the electrostatic repulsion between the dispersed phase particles,and the solid content is too high or too low,which will cause the stability of the emulsion to decrease.When the solid content is about 43%to45%,the epoxy resin emulsion has good stability.The viscosity of the prepared epoxy resin emulsion is relatively low,basically between 60 and 120 mPa·s.The viscosity of the emulsion decreases with the increase of water consumption,and increases with the increase of the emulsifier content,which is mainly related to the resistance of the dispersed phase internal molecules to the movement.So the optimum process condition for preparing waterborne epoxy resin emulsion is:water consumption 55%,emulsifier content 30%,emulsification temperature55°C,emulsification time 1h,and ultrasonic time 30 min.Under the optimal process condition,the prepared epoxy resin emulsion particles have a relatively regular solid spherical shape with small particle spacing,moderate solid content of the emulsion（45.4%）,low viscosity（76 mPa·s）.The storage stability and the dilution stability all can reach the standard,no delamination,precipitation occurs.（4）When the molar ratio of epoxy group to amine hydrogen is 1:1.5,and polyether amine D-400 is selected as the curing agent,the overall performance of the paint film is superior.Furthermore,after the addition of wetting agent,defoamer and curing accelerator,the actual drying time of the film is shortened by one hour,the hardness and adhesion are significantly improved,and the heat resistance of the film is improved.The curing film-forming process of waterborne epoxy coating,unlike traditional solvent-based epoxy coating,is a complex process involving both physical and chemical reactions.The specific process of curing film formation can be roughly summarized into four steps:1 water volatilization,chemical curing reaction between the curing agent and the surface of the latex particles;2 The water is further volatilized,the latex particles are close to each other,and the system gradually forms a regular three-dimensional network structure;3 The small molecule auxiliary and residual water in the system diffuse to the surface of the film to evaporate,the latex particles are closely packed,and the curing agent molecules diffuse into the latex particles to further chemical cross-linking reaction;4 The latex particles are deformed and condensed into a compact hexagonal structure to form a completely cured,uniform continuous paint film.