Fourier transform Raman difference spectroscopy for detection of lignin oxidation products in thermomechanical pulp.

Spruce thermomechanical pulp (TMP) was oxidized by the 2,2'azinobis-3-ethylbenzthiazoline-6-sulfonate cation radical (ABTS*+) in the presence and absence of oxygen. The pulp modification was monitored by Fourier transform (FT) Raman difference spectroscopy and other nondestructive spectroscopic methods. The ABTS*+ oxidative system resulted in modifications very similar to the laccase-ABTS-oxygen system, except for the FT-Raman results, which showed a difference in mechanisms attributed to a difference in produced Raman bands. Oxygen resulted in no oxygen-derived products, but only enhanced the production of a specific Raman band of several oxidation-produced bands. Detailed information on lignin reactions can be obtained from FT-Raman signals.