Investigation of the Chemistry of Oxygen Delignification of Low Kappa Softwood Kraft Pulp using an Organic/Inorganic Chemical Selectivity System Shiyu Fu, Jai M. Singh, Shuangfei Wang, and Lucian A. Lucia Georgia Institute of Technology, The Institute of Paper Science and Technology Center, Atlanta, Georgia, USA Abstract: Oxygen delignification (OD) of low kappa softwood kraft pulp was examined in two steps without inter-stage washing as part of an overall program to evaluate the efficiency of a selectivity enhancement system consisting of phenol and magnesium sulfate. Black liquor carryover in the reaction system did not substantially affect delignification and the selectivity of these OD reactions. The residual lignins from both the original pulp and oxygen-delignified pulp with and without the phenol/MgSO 4 selectivity enhancement system were prepared and characterized using NMR spectroscopy. The effluent lignins after oxygen delignification were also prepared and characterized. The lignin characterizations provided the basis for the rationalization of the selectivity observed. A significant finding of this study was that the phenol/MgSO 4 system in the oxygen delignification reaction appeared to hinder phenolic guaiacyl unit condensation. It also appeared to enrich the levels of p-hydroxyphenyls in the residual lignin. Keywords: Oxygen delignification, selectivity enhancement, NMR spectroscopy, GC-MS spectroscopy The authors gratefully acknowledge the United States Department of Energy for financial support (Contract DE-FC07-02ID14261) as well as the supporting companies of the Institute of Paper Science and Technology at the Georgia Institute of Technology. Address correspondence to Lucian A. Lucia, North Carolina State University, College of Natural Resources, Forest Biomaterials Laboratory, Campus Box 8005, 3108 Biltmore Hall, Raleigh, NC 27695-8005, USA. E-mail: lucian.lucia@ncsu.edu Journal of Wood Chemistry and Technology, 25: 95–108, 2005 Copyright # Taylor & Francis, Inc. ISSN 0277-3813 print/1532-2319 online DOI: 10.1080/02773810500191526 95