RADICALIZATION OF TMP FIBERS AND RELATED STRUCTURAL CHANGES

Abstract

Oxidation of TMP fibers at 298 K with molecular oxygen, in the presence of either [Co(salen)] in methanol or [Co(sulphosalen)] in water, were compared. Electron paramagnetic resonance (EPR) spectroscopy allowed to reveal and quantify the formation of phenoxy cobalt radicals in the former case and of phenoxy radicals in the latter. These radicals reach the same concentration after 60 min from the onset of reaction. Fiber integrity was more preserved after oxidation in water than in methanol, as assessed by heteronuclear single quantum coherence - nuclear magnetic resonance (2D-HSQC-NMR) spectroscopy, nuclear magnetic resonance spectroscopy of carbon (13C-NMR) and Gel Permeation Chromatography (GPC). These results suggest that also with water-soluble catalysts an efficient radicalization of fibers can be obtained. Thus, it is proposed that treatment with molecular oxygen in the presence of [Co(sulphosalen)] in water represents a promising way to approach an environmentally sustainable radicalization of fibers, without an heavy modification of the lignin structure.

Keywords

• Lignocellulosic fibers
• Phenols
• [Co(salen)]
• [Co(sulphosalen)]
• Radicals
• EPR
• NMR