Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (6): 1118-1128.doi: 10.3866/PKU.WHXB201503271

• SOFT MATTER • Previous Articles     Next Articles

Influence of Temperature on Microstructure and Physicochemical Properties of Alkali Lignin in Aqueous Solution

LI Hao, DENG Yong-Hong, ZHANG Xiao-Hong, QIU Xue-Qing   

  1. State Key Laboratory of Pulp and Paper Engineering, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China
  • Received:2015-03-02 Revised:2015-03-26 Published:2015-06-05
  • Contact: DENG Yong-Hong, QIU Xue-Qing E-mail:yhdeng08@163.com;xueqingqiu66@163.com
  • Supported by:

    The project was supported by the National Key Basic Research Program of China (973) (2012CB215302) and National Natural Science Foundation of China, (21436004, 21374032).

Abstract:

The effects of temperature on the microstructure and physicochemical properties of alkali lignin (AL) in alkaline aqueous solutions were studied at 20-60 ℃. The relationships between temperature and the physicochemical properties of AL, such as the aggregation morphology, molecular surface charge and hydrophobicity, intrinsic viscosity, adsorption characteristics on gas-liquid and liquid- solid interfaces were investigated experimentally using particle charge detection, dynamic light scattering, zeta plus measurements, viscometry, surface tension and dynamic contact angle measurements, quartz crystal microbalance, ultravioletvisible and fluorescence spectroscopies. As the temperature increases, the molecular surface charge density, the intrinsic viscosity, and surface tension of the AL solution decrease significantly. In contrast, the molecular hydrophobicity, intermolecular and intramolecular aggregations, and the amount of AL adsorbed onto liquid-solid interface increase. The AL molecular state changes from extended to compact with increasing temperature. Furthermore, when the temperature increases, the absolute value of the zeta potential first decreases, then increases, and then decreases again. Analysis suggests that the increase in temperature not only reduces the ionization degree of the weak acidic groups in AL, but also weakens the hydrogen bonds between ALmolecules and water molecules. These two factors lead directly to changes in the AL microstructure and physicochemical properties. Based on the results of this study, a mechanism for the microstructural changes in AL with changing temperature was proposed. It was concluded that water would transform from a good solvent to a poor solvent with decreasing temperature. Although AL is often viewed as an anionic surfactant, the regular changes in its physicochemical properties with temperature are more like those of a nonionic surfactant.

Key words: Alkali lignin, Temperature, Microstructure, Aggregation, Physicochemical property

MSC2000: 

  • O647