Adsorption Characteristics Of Sodium Lignosulfonate On Fiber And The Modification Of Lignin-based Dye Dispersant

Lignosulfonate is a kind of anion surface active agent containing benzene propane skeleton hydrophobic and hydrophilic functional groups such as sulfonic group. It is derived from an abundant and renewable resource and it could be used as dyestuff dispersant because of its physicochemical properties, such as solubility and dispersing performances. However, it would adsorb on fiber fabric surface and its dark brown color results in severe fiber staining which would limit its widely applications. Thus, study on the adsorption characteristics and mechanism of lignosulfonate on fiber surface has an important meaning for reducing the fiber staining and improving its application performances.Firstly, the adsorption isotherms of commercial sodium lignosulfonate(SL) on polyester fiber and the influences of temperature, p H, ionic strength and urea on the adsorption of SL on polyester fiber were investigated. The molecular weights of SL before and after adsorption were determined. The adsorption characteristics of SL on polyester fiber were determined by means of quartz crystal micro balances(QCM) and the adsorption model was established. The experimental results showed that the adsorption isotherms of SL conform to the Freundlich adsorption model. The adsorption capacity and quantity of SL on fiber decreased as the temperature increased. With the decreasing of p H value, the adsorption quantity increased while the adsorption intensity decreased. The adsorption quantity increased while the adsorption intensity decreased as ionic strength increased and the adsorption form tended to be multilayer adsorption. The adsorption quantity decreased markedly and the adsorption intensity also decreased with the addition of urea. The SL with lower molecular weight was first adsorbed on fiber under a lower temperature, while higher molecular weight was first adsorbed under a higher temperature. Based on the experimental exploration, it was concluded that SL absorbed by means of hydrogen bonding and hydrophobic interaction. The commercial SL was classified to four fractions by ultrafiltration and the adsorption characteristics of SL with different molecular weight were determined. The results indicated that the adsorption quantity order was that fraction with the molecular weight of 2.5~10k>fraction with the molecular weight of 10~50k>fraction with the molecular weight of more than 50k>fraction with the molecular weight less than 2.5k.Based on the adsorption characteristics researches of SL on fiber, the influences of dyeing conditions, inorganic salt and addition of hydrogen bond breaker on the fiber staining property of SL were investigated. The results showed that, the chromaticity of SL was deeper but the fiber staining degree decreased with the increasing of p H, and the fiber staining property increased with the temperature increasing. The hydrogen bonding played an important role in the fiber staining process, and fiber staining degree decreased markedly with the addition of urea. The SL fraction with the molecular weight of more than 50 k had the most serious fiber staining property and the fouling rate achieved to 7.76%. The fouling rate of fraction of SL with the molecular weight of 2.5~10k was 6.47%. The fouling rate of fraction with the molecular weight of 10~50k was 5.86%, and the fraction with the molecular weight of less than 2.5k had the weakest staining property and the fouling rate was 3.96%.The phenolic hydroxyl group of SL was blocked with epichlorohydrin and urea was added into the blocked SL to further decrease the staining degree of SL on fiber, then the elevated temperature dispersion performance of the thus treated SL was improved by means of aliphatic alcohol addition, and the final modified product GSL was prepared. The structures and properties of GSL, SL and commonly used commercial dyestuff dispersant Ultrazine Na(UNA) and Guo Tai dispersant were tested by ultraviolet, gel permeation chromatography, automatic potentiometric titration, Datacolor color measurement and laser particle size instrument, and so on. The adsorption characteristics and adsorption morphology of dye dispersants on dyestuff and fiber surface were measured via QCM and AFM.The results showed that, the fiber staining property of GSL was weaker than SL, and the fouling rate decreased from 5.07% of SL to 2.21%. The fouling rate of GSL was far below that of the domestic commonly used lignin-based dispersant with the fouling rate of 6.83%, and was close to that of the foreign SL dispersant. The adsorption morphology of SL on dye surface was sparse and the adsorption film was rough, while the adsorption film of GSL on dye surface was dense, uniform and the roughness was low. Hence, the elevated temperature dispersion performance and dyeing rate of GSL was optimal.