Lignin modification during Eucalyptus globulus kraft pulping followed by totally chlorine-free bleaching: a two-dimensional nuclear magnetic resonance, Fourier transform infrared, and pyrolysis-gas chromatography/mass spectrometry study.
Chemical modification of eucalypt lignin was investigated during kraft pulping and chlorine-free bleaching by comparing milled wood lignin, kraft lignin, and pulp enzymatic residual lignins. The syringyl-to-guaiacyl ratio (S/G) from analytical pyrolysis slightly changed during pulping and bleaching (S/G, 3-4) but was higher in the kraft lignin. Semiquantitative heteronuclear single quantum correlation (HSQC) nuclear magnetic resonance (NMR) showed that the relative amount of beta-O-4' (around 80% side chains) and resinol type substructures (15%) was slightly modified during pulping and oxygen delignification. However, a decrease of resinol substructures (to only 6%) was found after alkaline peroxide bleaching. The relative amount of surviving linkages in the highly phenolic kraft lignin was dramatically modified; resinols were predominant. Oxygen delignification did not change interunit linkages, but a relative increase of oxidized units was found in the HSQC aromatic region, in agreement with the small increase of pyrolysis markers with oxidized side chains. NMR heteronuclear multiple bond correlations showed that the oxidized units after oxygen delignification bore conjugated ketone groups.
Ibarra
David
D
Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain.
Chávez
María Isabel
MI
Rencoret
Jorge
J
Del Río
José Carlos
JC
Gutiérrez
Ana
A
Romero
Javier
J
Camarero
Susana
S
Martínez
María Jesús
MJ
Jiménez-Barbero
Jesús
J
Martínez
Angel T
AT
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005052:Eucalyptus / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000737:chemistry; D008031:Lignin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010100:Oxygen / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014934:Wood / Q000737:chemistry*
D008031:Lignin; D006861:Hydrogen Peroxide; D010100:Oxygen