Bleached cellulosic fibers produced from wood are mainly used for paper production. A slight <br />proportion is devoted for chemical uses. Nevertheless this application offers a better added value and <br />is interesting for the development of the future biotextiles and bioplastics. The limitations of the <br />chemical uses of these fibers are their high hemicelluloses content, their low reactivity, their high <br />polymerization degree and the presence of residual lignin. Moreover the current bleaching processes, <br />implemented in pulp mills, still use chlorinated agents, very efficient, but at the origin of toxic organic <br />halogenated compounds. The objective of this project is to develop a catalytic process of bleaching and <br />purification using hydrogen peroxide as main delignifying agent, able to degrade residual lignin and <br />to eliminate hemicelluloses in order to lead to reactive celluloses of variable polymerization degrees. <br />This environmentally friendly process would be implemented in parallel of the paper pulp production <br />line and would allow the pulp and paper industry to produce chemical celluloses with high added <br />value.
The copper-phenanthroline complex has a catalytic action on hydrogen peroxide (H2O2) reactions with
impure cellulosic fibers in alkaline medium: delignification is improved and the carbohydrates are
more oxidized which could lead to hemicelluloses solubilization and to a greater cellulose
depolymerization. The mechanism of the catalysis that relates both lignin and carbohydrate
degradation should be studied to better control its effects and to direct the research towards new more
efficient or cheaper catalysts. The complexity of the fibers, of the lignin and carbohydrate structure
imposes first to work on model compounds that have been synthesized for the project. The catalysts
are then applied on industrial cellulose fibers in association with complementary treatments to reach
the specifications imposed by the various applications of cellulose (textiles, cosmetics …). All the
developed process should be implemented in a pulp mill.
The study of the catalyzed H2O2 delignification by the copper-phenanthroline complex, conducted on
lignin model compounds, led to the proposal of a mechanism explaining the higher depolymerization
of lignin in the presence of the catalyst. Moreover, a ligand screening of polyimine type shows that
copper-phenanthroline type complexes are the most efficient catalysts. A bleaching sequence for the
production of pure cellulose from Kraft pulp has been developed. It includes a hydrogen peroxide
delignification step catalyzed (or not), and pre - and post- chlorine free treatments. The produced
celluloses do not contain any more impurity and possess required molecular weight for several
chemical applications. Finally, a technical and economical evaluation of the proposed process was
The results of the project were disseminated in two international conferences focusing on polymer
science and on the chemistry of wood and cellulose fibers.
Two articles at least will be submitted for publication. They will focus (1) on the mechanism of the
catalyzed delignification, (2) on the ligand screening as well as (3) on the development of the
bleaching sequence using hydrogen peroxide for the production of pure cellulose from wood. These
papers will be proposed for publication in journals specialized in catalysis and natural polymers.
Nathalie MARLIN (INSTITUT NATIONAL POLYTECHNIQUE DE GRENOBLE - INPG)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
UNIVERSITE GRENOBLE I [Joseph Fourier]
INSTITUT NATIONAL POLYTECHNIQUE DE GRENOBLE - INPG
Help of the ANR 600,529 euros
Beginning and duration of the scientific project: - 36 Months