Techniques for characterizing lignin

Abstract

Many techniques are available to characterize lignin. The techniques presented in this chapter are considered nondegradative, which are commonly applied to lignin. A brief discussion of lignin structure is included with this chapter to aid the reader in understanding why the discussed characterization techniques are appropriate for the study of lignin. Because the chemical structure and composition of lignin vary from source, type of lignin, and isolation method, as discussed in the preceding chapters, characterization is important. Obtaining the molecular weight of a lignin sample can give information, such as degree of polymerization, even before investigating the chemical structure. Chemical structure characterization is most often accomplished using spectroscopic methods. Understanding the chemical structure can be useful in determining lignin sources, degradation of lignin samples, relationship between physical properties and thermal properties, selecting appropriate modification methods, and determining the efficacy of modifications. Chemical structure characterization techniques discussed in this chapter include ultraviolet (UV) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Physical properties such as thermal and mechanical properties can be related back to the chemical structure. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) are often employed during the investigation of thermal properties of lignin, while dynamic mechanical analysis (DMA) can be used to investigate both thermal and mechanical properties. In each section, a brief introduction to each technique is followed by examples of its application to lignin. Finally, the reader is directed toward select resources that are available for a more complete understanding of these methods, and their applicability to lignin.

Citation

Stark, Nicole M.; Yelle, Daniel J.; Agarwal, Umesh P. 2016. Techniques for characterizing lignin. In: Lignin in Polymer Composites. Faruk, Omar; Sain, Mohini, eds. Elsevier; Kidlington, Oxford. Chapter 4: 49-66.