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December 14, 2016
Jordan Perrin, Ph.D. student of LGP2, defended his doctoral thesis: "Production of pure cellulose from wood by green purification and bleaching process with ozone, for textile and chemical application".
Bleaching of wood pulp is still an environmental issue. A new ozone-based TCF bleaching sequence made it possible to produce a bleached dissolving pulp whose properties were comparable to those of a pulp bleached with a conventional bleaching sequence using chlorine dioxide (ECF).
It was noticed that the TCF bleached pulp had better brightness stability. The origin of yellowing is still poorly understood. It was studied here by the implementation of several analytical methods including EPR spectroscopy, UV-Raman spectroscopy for the analysis of aromatic and quinone residues and also fluorescence spectroscopy for the measurement of carbonyl and carboxyl groups. It was shown that the carbonyl groups present on the cellulose are detrimental to the brightness stability, both during accelerated ageing and mercerization. They can be partly eliminated by an alkaline treatment, which in return improves the brightness stability. Addition of hydrogen peroxide allows for a further increase of the brightness stability, but without any extra carbonyl removal.
Hydrogen peroxide would have an effect on some conjugated residual chromophores, mainly quinones, involved in the yellowing mechanism. The TCF pulp would possess less quinones than a ECF pulp.
The thesis was supported by ADEME, the French Environmental Agency, and two major players in ozone generation (Xylem and Degremont-Ozonia)