C-13 CP MAS NMR-STUDY OF PHOTODEGRADED STONEGROUND WOOD PULP

Unbleached and alkaline hydrogen peroxide bleached black spruce (Picea mariana) stoneground wood pulps were subjected to severe irradiation. Photodegradation of lignin in these pulps was investigated by dipolar dephasing solid state C-13 CP/MAS NMR spectroscopy The irradiation caused a significant loss in lignin aromaticity. Based on the different chemical shifts attributable to etherified and non-etherified guaiacyl structures, the loss of lignin aromaticity was interpreted in terms of these two structures; the contribution of each structure to the reduction in lignin aromaticity was different depending on whether the samples were unbleached or alkaline hydrogen peroxide bleached. These observations were substantiated by photoacoustic FT-IR spectrometry and conductometric titrations.