ABSTRACT
Introduction ............................................................................................................ 104 Vibrational Spectroscopy .................................................................................. 104 Application to Lignin ........................................................................................ 105
Raman Spectroscopy .............................................................................................. 107 Background ....................................................................................................... 107 Instrumentation ................................................................................................. 108 Special Techniques and Effects ......................................................................... 108
Micro Raman ................................................................................................ 108 Raman Imaging ............................................................................................ 108 Resonance and Preresonance Raman ........................................................... 109 Conjugation Effect........................................................................................ 109 Surface Enhanced Raman ............................................................................. 109
Spectral Interpretation ....................................................................................... 109 3100-2800 cm−1 ........................................................................................... 110 1800-1500 cm−1 .......................................................................................... 112 1500-1000 cm−1 ........................................................................................... 113 1000-350 cm−1 ............................................................................................. 113 UV Resonance Raman Spectra..................................................................... 113
Applications ...................................................................................................... 113 Lignin in Wood ............................................................................................. 113 Lignin in Mechanical Pulp and Paper .......................................................... 114 Residual Lignin in Chemical Pulp ............................................................... 115 Lignin in Other Lignocellulosics .................................................................. 115 Commercial Lignins ..................................................................................... 115 Chemical Modication Reactions of Lignin ................................................ 116 Lignin Quantitation ...................................................................................... 116
Mid-Infrared Spectroscopy .................................................................................... 117 Background ....................................................................................................... 117 Instrumentation ................................................................................................. 118 Special Techniques/Interfaces ........................................................................... 118
Diffuse Reectance ...................................................................................... 118 Attenuated Total Reection, or Internal Reectance ................................... 119 IR Microscopy .............................................................................................. 119 Chemical Imaging ........................................................................................ 119 2-D IR ........................................................................................................... 119
Vibrational spectroscopy is an important tool in modern chemistry. In the past two decades, thanks to signicant improvements in instrumentation and the development of new interpretive tools, it has become increasingly important for studies of lignin. This chapter presents the three important instrumental methods-Raman spectroscopy, infrared (IR) spectroscopy, and near-infrared (NIR) spectroscopyand summarizes their contributions to analytical, mechanistic and structural studies of lignin. The conceptual frameworks used to interpret vibrational spectra are rst described in the following section.
