磺化木质素系聚合物的结构及其在氧化铝上的吸附特性

以造纸黑液中的碱木质素为主要原料,通过磺化和缩聚反应制备了磺化木质素高分子聚合物SBAL.TEM和1H-NMR测试结果表明SBAL是以木质素的疏水骨架为中心,以磺酸基和羧基组成亲水性侧链的球形结构.GPC测试结果表明其重均分子量达到了24880 Da,是碱木质素的7.38倍,电位滴定测试结果表明,其磺化度达到2.70 mmol.g-1.通过流变曲线、吸附等温线、zeta电位、XPS测试研究了其对氧化铝在水中的分散机理及其吸附特性.掺SBAL的氧化铝浆体,在pH=3～12范围内SBAL对其具有良好的分散降黏作用.溶液pH对SBAL的分子构型和吸附特性有较大的影响,随pH增加,SBAL中磺酸基、羧基和酚羟基逐渐电离,分子的伸展程度逐渐增大.随pH增加,SBAL在氧化铝上的吸附质量减少,吸附层由致密逐渐变得疏松,pH小于等电点时以静电吸附为主,pH大于等电点时以非静电的特性吸附为主.当SBAL的用量小于临界值(0.5 wt%)时,其在氧化铝表面形成单分子层吸附,在颗粒间起到静电排斥作用;当用量大于临界值时,其在颗粒表面形成聚集体吸附而起到空间位阻作用.

THE STRUCTURE CHARACTERISTICS OF SULFONATED LIGNIN-BASED POLYMER AND ITS ADSORPTION PROPERTIES ON ALUMINA

A sulfonated lignin-based polymer,SBAL,was prepared by sulfomethylation,etherification and polycondensation reaction using alkali lignin from the alkaline pulping spent liquor of bamboo as main material.TEM and 1H-NMR results showed that the structure of SBAL was loose spherical,the center of which was the hydrophobic skeletons of lignin,the long side chains with sulfonic and carboxyl groups were distributed on its surface.GPC and potentiometric titration results showed that the Mw of SBAL reached 24880 Da,7.38 times of the alkali lignin,and the sulfonic group content was 2.70 mmol·g-1.The adsorption properties and the dispersion efficiencies of SBAL were investigated by means of isothermal adsorption,XPS,zeta potential and rheological experiments.At pH 3～12,the SBAL as dispersant can remarkably reduce the viscosity of alumina slurry.The sulfonic,carboxyl and phenolic hydroxyl groups of SBAL are ionized gradually as pH increasing,which makes the SBAL molecule chains spread well in the alkali condition.With the increase of pH,the adsorption amount of SBAL on alumina particles decreases and the adsorption configuration changes from compact to loose.When pH is lower than isoelectric point of alumina,the main adsorption force between SBAL and alumina particle is electrostatic adsorption,however,when pH is more than isoelectric point,non-static specific adsorption dominates the main force.When the dosage of SBAL is less than the critical dosage(0.5 wt%),SBAL generates an electrostatic repulsion between particles by monolayer adsorption on alumina surface,moreover,when the SBAL dosage is more than the critical one,SBAL may adsorb on alumina particles in the form of aggregation and improve the steric hindrance action.