The residual lignins extracted from both the original and oxygen-delignified softwood kraft pulp and those isolated from the effluent of oxygen delignification were subjected to pyrolysis in the presence of tetramethylammonium hydroxide(TMAH).The methylated products were analyzed with gas chromatography-mass spectrometry(GC-MS) to investigate the molecular characterization and changes of the residual lignins in softwood kraft pulp during oxygen delignification.The results indicated that pyrolysis of the lignins yielded primarily methylated guaiacyl derivatives.Oxidation under alkali oxygen conditions could induce fragmentation in lignin and produce more acid groups

and the lignin molecules with short side chains(C1 and C2) could be preferentially removed from pulps during oxygen delignification.