RADICAL FORMATION ON CTMP FIBERS BY ARGON PLASMA TREATMENTS AND RELATED LIGNIN CHEMICAL CHANGES

The changes at molecular level induced by cold argon plasma treat-ments on fibers obtained from chemi-thermo-mechanical pulp (CTMP) fibers were investigated. The radicals formed on CTMP fibers after treatments were identified and quantified by Electron Paramagnetic Resonance (EPR) spectroscopy. The plasma conditions which maximize the formation of radicals on fibers were assessed: after treatment with 0.4 mbar Ar pressure and 75 W radiofrequency power, phenoxy radicals triple their concentration in only 60 s and reach a value 4 times higher than that reported for laccase-catalyzed lignin oxidation. It was found that in plasma-treated fibers, the formation of radicals competes with their coupling. This latter result leads to cross-linkages of the lignin mono-meric units and formation of new intermonomeric C-C and C-O bonds, for the first time assigned to specific molecular interactions through Heteronuclear Single Quantum Coherence (2D-HSQC) spectroscopy and Nuclear Magnetic Resonance spectroscopy of carbon (13C-NMR). These results were confirmed by Nuclear Magnetic Resonance spectros-copy of phosphorous (31P-NMR). The lack of evidences of inter-fiber bond interactions, deduced from Gel Permeation Chromatography (GPC) data, suggests the possible application of plasma treatments for the production of wood fiber-based composites

Oxidation of Isoeugenol by Salen Complexes with Bulky Substituents

The catalytic properties of bulky water-soluble salen complexes in the oxidation of isoeugenol (2-methoxy-4-(1-propenyl) phenol) have been investigated in aqueous ethanol solutions in order to obtain a mixture of polymeric compounds through dehydrogenative polymerization. The average molecular weight of dehydrogenated polymers (DHPs) was monitored by GPC and correlated to reaction conditions such as time, concentration of substrate, concentration of catalyst, type of oxidation agent, etc. The DHP synthesized by adopting the best reaction conditions was characterized by different analytical techniques (GPC, 13C-NMR, 31P-NMR and LC-MS) to elucidate its structure. The lignin-like polymer resulting from isoeugenol radical coupling possesses valuable biological activity and finds applications in a variety of fields, such as packaging industry and cultural heritage conservation

A multi-analytical study of degradation of lignin in archaeological waterlogged wood

Historical or archaeological wooden objects are generally better conserved in wet environments than in other contexts. Nevertheless, anaerobic erosion bacteria can slowly degrade waterlogged wood, causing a loss of cellulose and hemicellulose and leading to the formation of water-filled cavities. During this process, lignin can also be altered. The result is a porous and fragile structure, poor in polysaccharides and mainly composed of residual lignin, which can easily collapse during drying and needs specific consolidation treatments. For this reason, the chemical characterization of archaeological lignin is of primary importance in the diagnosis and conservation of waterlogged wood artifacts. Current knowledge of the lignin degradation processes in historical and archaeological wood is extremely inadequate. In this study lignin extracted from archaeological waterlogged wood was examined using both Py-GC/MS, NMR spectroscopy and GPC analysis. The samples were collected from the Site of the Ancient Ships of San Rossore (Pisa, Italy), where since 1998 31 shipwrecks, dating from 2nd century BC to 5th century AD, have been discovered. The results, integrated by GPC analysis, highlight the depolymerization of lignin with cleavage of ether bonds, leading to an higher amount of free phenol units in the lignin from archaeological waterlogged wood, compared to sound lignin from reference wood of the same species

RADICALIZATION OF TMP FIBERS AND RELATED STRUCTURAL CHANGES

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

Chemical characterisation of the whole plant cell wall of archaeological wood: an integrated approach

Wood artefacts undergo complex alteration and degradation during ageing, and gaining information on the chemical composition of wood in archaeological artefacts is fundamental to plan conservation strategies. In this work, an integrated analytical approach based on innovative NMR spectroscopy procedures, gel permeation chromatography and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC-MS) was applied for the first time on archaeological wood from the Oseberg collection (Norway), in order to evaluate the chemical state of preservation of the wood components, without separating them. We adopted ionic liquids (ILs) as non-derivatising solvents, thus obtaining an efficient dissolution of the wood, allowing us to overcome the difficulty of dissolving wood in its native form in conventional molecular solvents. Highly substituted lignocellulosic esters were therefore obtained under mild conditions by reacting the solubilised wood with either acetyl chloride or benzoyl chloride. A phosphytilation reaction was also performed using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholan. As a result, the functionalised wood developed an enhanced solubility in molecular solvents, thus enabling information about modifications of lignin, depolymerisation of cellulose and structure of lignin-carbohydrate complexes to be obtained by means of spectroscopic (2D-HSQC-NMR and 31P-NMR) and chromatographic (gel permeation chromatography) techniques. Py-GC-MS was used to investigate the degradation undergone by the lignocellulosic components on the basis of their pyrolysis products, without any pre-treatment of the samples. The application of all these combined techniques enabled a comprehensive characterisation of the whole cell wall of archaeological wood and the evaluation of its state of preservation. High depletion of carbohydrates and high extent of lignin oxidation were highlighted in the alum-treated objects, whereas a good preservation state was found for the untreated wood of the Oseberg ship. [Figure not available: see fulltext.