The Dynamic Adsorption Behavior And Regulation Of Lignosulfonate At The Interfaces

Amphiphilic polymer refers to the macromolecular compound which has both thehydrophilic and hydrophobic properties in the molecular chain. The better dual performances（polymer and amphiphilic molecular structure） may play an important role in protectingcolloid, dispersing, flocculating and so on, and it has been widely used in various industrialprocesses such as domestic chemicals, coatings technology, medicines, textile and dyeingindustry, architecture, etc. Recently, as the domestic and overseas people increasing value theenvironmental pollution and hazards to human health caused by chemical products, ligninamphiphilic polymer has been attracted a lot of attention and become one of the hot topics inacademic areas for the characteristics of renewable and biodegradability.The lignin amphiphilic polymers are mainly from two kinds of byproducts in thepapermaking industry:（1） lignosulfonates, from the traditional sulphite-pulping method, is awater soluble polyelectrolyte owing to the introduced sulfonic group;（2） alkaline lignin,comes from the soda chemi-pulping or kraft pulping, is only dissolved in the alkaline solutionbut can be modified by the sulfonation reaction to improve the water solubility, reactiveactivity and dispersing performance.One of the largest applications of the lignin amphiphilic polymers is used as the dispersantin the suspension, and the dispersing performance mainly depends on the adsorptionbehaviors of lignin amphiphilic polymers on the surface of solid particles, thus research andenunciation of the adsorption characteristics and the adsorption mechanisms, especially forthe adsorption configuration and the adsorption law, has important instructive significanceand reference value on the modification of lignin amphiphilic polymers and the improvementof its surface physicochemical property. However, the heterogeneity of molecular structure oflignin amphiphilic polymers not only brings difficulties to characterization of property, butmakes the molecular interactions more complex, including the interaction between polymerand polymer, the interaction between of polymer and solvent molecule, and the interactionbetween polymer and solid surface. Therefore, until now, for the lignin amphiphilic polymers,there are still a lot of basic theoretical problems need to be resolved.In the thesis, sodium lignosulfonate （SL） was used as the material, the dynamic adsorptionbehavior of SL on the air-water interface was studied, and the adsorption driving force of SLon Al₂O₃particles surface at different pH values was explored, and the effect of molecularconfiguration on the dispersing performance of Al₂O₃suspension was analyzed. Based on the results, the influences of straight-chain alcohols on the dispersion performance and adsorptionproperty of SL on the Al₂O₃particles were studied. Moreover, a sulfonated lignin-basedmacromolecule polymer, SBAL, was prepared by chemical reaction using alkali lignin fromthe alkaline pulping spent liquor of bamboo as main material. The adsorption properties andthe dispersion efficiencies of SBAL on the Al₂O₃particles in aqueous solution wereinvestigated, and the research results can provide basic data and theoretical guides for theindustrial application of the lignin amphiphilic polymers.The dynamic adsorption behavior of SL aqueous solutions with different concentration atthe air-water interface was investigated using an axisymmetric drop shape analysis-profilemethod. The result showed that the adsorption of SL at the air-water interface was a slowprocess, and the adsorption efficiency depended largely on the depolymerization rate of SLaggregate in the aqueous solution. The data were analyzed by the Langmuir, Frumkin,modified Frumkin and modified Flory-Huggins equations, and the results indicated that theadsorption amount of SL at the interface was smaller, and the molecular configuration of SLwas looser, and the intermolecular force of SL in the adsorption layer was very weak whichcan be negligible. The expression for estimating the dynamic surface tension of SL aqueoussolution was also presented.The film-forming characteristic of SL at the air-water interface was investigated byLangmuir-Blodgett （LB） technique. The results showed that the Langmuir film of SL can betransferred successfully onto the hydrophilic quartz substrate under the proper experimentalconditions: the concentration of SL was10g/L, the subphase solution was the0.01mol/LCdCl₂, the sample volume was50μL and the compression speed was10mm/min. Besides, itwas confirmed that the straight-chain alcohols can improve the adsorption amount of SL at theair-water interface, the synergistic effect between SL molecules and straight-chain alcoholsmade rearrangement of the SL molecular structure at the interface more ordered.The adsorption behaviors and dispersion efficiencies of SL on Al₂O₃particles at differentpH values were investigated by UV-Vis spectroscopy, zeta potential, X-ray photoelectronspectroscopy （XPS） and rheological measurements. Results showed that at low pH values, asconcentration increased, SL adsorbed on the Al₂O₃particles in the form of aggregate and theadsorption isotherms belonged to the Freundlich equation; at high pH values, SL adsorbed inthe form of loose single-molecular configuration and the adsorption isotherms belonged to theLangmuir equation. At pH3¹1, the adsorption was not affected through addition of urea,ruling out hydrogen bond as the controlling factor. The adsorption mechanism of SL on theAl₂O₃particles was related to the isoelectric point of Al₂O₃. The main driving force was considered as the synergistic effect of the electrostatic interaction and the Al3+-π interactionwhen pH <pHIEP, while the Al3+-π interaction was the dominant driving forces when pH>pHIEP. The dispersing mechanism was mainly attributed to the steric hindrance （pH <pHIEP）and the electrostatic repulsive force （pH> pHIEP） owing to the differences of adsorbedconfiguration.The effect of straight-chain alcohols on the aggregation of SL in the aqueous solution wasstudied by the zeta potential, surface charge density and transmission electron microscope（TEM）. The results showed that nonpolar end-group of the straight-chain alcohols could insertinto the hydrophobic core of SL molecule or aggregates, the straight-chain alcohols helped theSL aggregation depolymerize in the aqueous solution, made the wrapped hydrophilic groupsexposed and improved the electronegativity of SL molecules. The adsorption isotherms, zetapotential and XPS results showed that the addition of straight-chain alcohols could increaseeffectively the electrostatic repulsive force between Al₂O₃particles. When suspensions werecarried on in the acidity or neutral solution, the straight-chain alcohols were favorable for theAl₂O₃particles dispersion in the aqueous solution, however, the effect of the straight-chainalcohols could be almost negligible when the suspension in the alkaline solution.SBAL, with higher sulfonation degree and higher molecular weight, was prepared by thesulfomethylation, etherification and polycondensation reactions. TEM and1H NMR resultsshowed that the structure of SBAL was loose spherical, the center of which was thehydrophobic skeletons of lignin, the long side chains with sulfonic and carboxyl groups weredistributed on its surface. GPC and potentiometric titration results showed that the MwofSBAL reached24880Da,7.38times of the alkali lignin, and the sulfonic group content was2.70mmol g1. The adsorption properties and the dispersion efficiencies of SBAL wereinvestigated by means of adsorption isotherms, XPS, zeta potential and rheologicalexperiments. At pH3¹2, SBAL as the dispersant can remarkably reduce the viscosity ofAl₂O₃suspension. The sulfonic, carboxyl and phenolic hydroxyl group of SBAL were ionizedgradually as pH increasing, which made the SBAL molecule chain spread well in the alkalicondition. With the increase of pH, the adsorption amount of SBAL on the Al₂O₃particlesdecreased and the adsorption configuration from compact became loose. When pH <pHIEP,the main adsorption force between SBAL and Al₂O₃particle was electrostatic adsorption,however, when pH> pHIEP, non-static specific adsorption dominated the main force. Whenthe dosage of SBAL was less than the critical dosage （0.5%）, SBAL generated an electrostaticrepulsion between particles by monolayer adsorption on Al₂O₃surface, however, when the dosage was more than the critical dosage, SBAL absorbed on Al₂O₃particles in the form ofaggregation to improve the steric hindrance.