abstract
The focus of this study is the chemistry of reductive bleaching of kraft pulps with sodium dithionite. A set of model compounds mimicking quinone structures, residual lignin structures with conjugated carbonyl/carboxyl groups and muconic acid, among others, was reduced with sodium dithionite and monitored by ultraviolet-visible (UV-vis) spectroscopy. Depending on the chromophore models, either reductive or sulfonation reactions are thought to be responsible for the degradation. No reductive degradation of hexeneuronic acid (HexA) residues was detected, but unsaturated structures of unknown origin were eliminated from the xylan. Additionally, the potential of the reductive stage with either sodium dithionite or sodium borohydride was tested using an industrial pine kraft pulp bleached by OOZEDD sequence. This pulp, with a 88.8% ISO brightness ceiling, exhibited a brightness increase to 90 +/- 0.5% in the final reduction stage.
keywords
RESONANCE RAMAN-SPECTROSCOPY; HEXENURONIC ACID; SULFITE; LIGNIN; IDENTIFICATION; KINETICS
subject category
Materials Science
authors
Carreira, HJM; Loureiro, PEG; Carvalho, MGVS; Evtuguin, DV
our authors
Dmitry Evtyugin
Associate Professor with Aggregationacknowledgements
We thank FCT (Portuguese Foundation for Science and Technology) and UE - FEDER (European Fund for Regional Development) through the Competitiveness Factors Operational Programme (COMPETE) for the financial support of this work within the scope of Project PTDC/EQU-EQU/113547/2009 (COMPETE, ref. FCOMP-01-0124-FEDER-015254). We also thank the POPH-QREN funding program and FCT-MCTES for the post-doctorate degree grant SFRH/BPD/77882/2011. Celtejo mill is acknowledged for supplying the pulps used in this study.