Structural Characterization, Adsorption and Dispersion Properties of Sodium Lignosulfonate by Horseradish Peroxidase Incubation†

Abstract

A novel and efficient polymerization of lignosulofonate(by-products from sulfite pulping process) was investigated in the present study. The ability of commercial horseradish peroxidase(HRP) for polymerizing sodium lignosulfonate(SL) was investigated in aqueous solution at room temperature. The gel permeation chromatography(GPC),potentiometric titration,infrared spectroscopy(IR),and1H nuclear magnetic resonance(1H NMR) were used the structural characterization of SL. GPC results showed a significant increase in molecular weight(Mw) of SL. With different dosages of HRP added,SLs with different Mwcould be obtained. When 6 g/L HRP was added,the Mwof SL could increase by 155%. During the HRP incubation,phenolic groups were oxidized to phenoxyl radicals. These radicals could undergo radical-couplings directly. On the other hand,unbound electron could transfer to the para- and ortho-carbon of the phenols and β-carbon of the branch,undergoing radical-couplings. Among the radical-couplings,β-O-4' and β-β' were the predominant. Moreover,the sulfonic group increased by 27% after HRP incubation. The adsorption of SL by HRP incubation was studied by electrostatic self-assembly technology. After HRP incubation,the adsorption amount of SL increased significantly. Further,because of the increase of Mwand sulfonic group content,resulting in the stronger steric hindrance and electronic repulsion,the dispersion ability of SL on TiO2slurry was improved.