Academic literature on the topic 'Acetylated lignins'

Lignin was isolated from aspen bleached chemithermomechanical pulp by employing a mild acid hydrolysis procedure, and the extracted material was acetylated with acetic anhydride. Nuclear magnetic resonance analyses indicated that the relative ease of acetylating lignin hydroxyl groups was phenolic >> γ-side chain > α-side chain. Non-acetylated and acetylated lignins were impregnated onto cellulosic test sheets, and the photo-behavior of the lignins was examined under irradiation with two light sources, a fluorescent lamp and a black lamp. Optical reflective studies indicated acetylation efficiently inhibited the photodiscoloration of aspen bleached chemithermomechanical pulp lignin under visible and near-UV light irradiation. The photostability of the lignin was correlated to the extent of lignin acetylation. The observed photo-stabilization of acetylated lignin during light irradiation was attributed to the acetylation of phenoxy and aliphatic hydroxyl groups in lignin.Key words: green chemistry, hardwood lignin, acetylation, photo-stabilization, photoyellowing, NMR.

Abstract For ground pulp (GP) utilization in wood fiber composites as reinforced material, its thermal behavior is relevant. The contribution of lignin to thermal performance of GP from Pinus densiflora was the focus of the present study. Dimeric lignin model compounds and isolated milled wood lignins (MWLs) from three sources were submitted for thermogravimetric analysis (TGA). The temperatures leading to 1% weight loss (T per 1% WL) for the material were determined. The thermal stability of β-O-4 models was the lowest. Among the MWLs, the abaca MWL with its high β-O-4 content was the least thermostable. An acetylated nonphenolic β-O-4 lignin model compound showed that acetylation improves the thermal stability of this type of dimeric models. The acetylation of benzylic OH groups in β-O-4 linkages is especially relevant for the thermal resistance, which was also shown based on pre-acetylated benzylic OH groups in the GP before the total acetylation.

AbstractA novel lignin-based slow release fertilizer with low environmental impact has been developed. More precisely, a granulated simple superphosphate fertilizer, consisting of calcium phosphate monobasic [Ca(H2PO4)2·H2O] and gypsum (CaSO4·2H2O) was coated with modified kraft lignins and the diffusion of phosphorus was observed as a function of time. The lignin was hydroxymethylated with formaldehyde and subsequently cross-linked with phenol-formaldehyde resin resulting in HML-PF as coating. Moreover, coating films were prepared from a mixture of acetylated lignin (Lac) and acetylated cellulose (Cellac). Both coatings show similar permeability to calcium phosphate and controlled effectively the P-release, particularly at the initial stages of the experiment. The P-release was linear in the decay phase but there is no lag time in the process. A significant P amount was not released from the particles coated with HML-PF, i.e. 80–50% remained irreversible bound, depending on the coating formulation. The maximum fractional P-release varied among the different coatings tested. Phosphorus is partly retained inside the slightly soluble calcium sulfate matrix.

AbstractConiferyl alcohol is considered to be a potent antioxidant and a precursor of several bioactive products. In addition, it is a frequently used as a model compound in lignin chemistry. Coniferyl thiol is used analogously to study the sulfur chemistry in technical lignins. Coniferyl alcohol was synthesized in a large scale from commercially available ferulic acid by a mixed anhydride reduction method which affords high yields (84%) under very mild conditions and allows using sodium borohydride. The nucleophilic substitution of 4-O-acetylated coniferyl alcohol (3) with thioacetic acid in the presence of dimethylformamide (DMF) dineopentylacetal afforded 4-O-acetylated coniferyl thioacetate (5) in a 70% yield, which, in a 72% yield, was deprotected to the respective thiol (6). Both coniferyl alcohol and coniferyl thiol were comprehensively analytically characterized [one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy]. The presented approach renders the two model substances readily available on a gram scale and according to low-risk, environmentally compatible protocols.

AbstractSize exclusion chromatography with multi-angle laser light-scattering detectors was applied for acetylated softwood and hardwood kraft lignins (Ac-SKL and Ac-HKL) and 8-O-4′ type of linear polymeric lignin model (Ac-M-8O4′) to compare their swelling behaviors. The plot of molar mass (MM) vs. retention time for Ac-M-8O4′ was similar to that of polystyrene, which revealed that Ac-M-8O4′ exhibited swelling behavior that was similar to that of polystyrene. However, the MM values of both Ac-KLs were larger than those of polystyrene standards at any retention time. This difference indicated that both Ac-KLs had a more compact structure than those of polystyrene and Ac-M-8O4′. One hypothesis is that the larger MM of both Ac-KLs stems from their branched structures. To verify this hypothesis, the frequency of 5-5′ interunit linkage in lignin samples was determined by 1H NMR after nitrobenzene oxidation. A linear relationship between MM and 5-5′ abundance was observed in the high MM region.

Abstract Milled wood lignins (MWL) were isolated from the stem (MWLS) and pith (MWLP) of bamboo (Phyllostachys pubescens). The nonacetylated and acetylated bamboo MWLs were investigated by Fourier transform infrared, quantitative 13C-nuclear magnetic resonance (NMR), 2D heteronuclear single quantum coherence (HSQC) NMR, and 31P-NMR spectroscopy. The MWL consists of p-hydroxyphenyl (1–2%), guaiacyl (21–31%), and syringyl (67–78%) units associated with p-coumarates and ferulates. A modified quantitative 13C-NMR and 2D-HSQC analysis has demonstrated that the predominant intermonomeric linkages are of the type β-O-4 (45–49 per 100 C9 units, i.e., per C900) along with small amounts of other structural units such as resinols (3.6–7.4 per C900), tetrahydrofuran (2.0–2.3 per C900), phenylcoumaran (2.8–4.5 per C900), spirodienones (1.3–2.3 per C900), and α,β-diaryl ethers (2.8–2.9 per C900). MWLP contained more p-coumarates than MWLS. The various degrees of γ-acylation (17–27%) were positively associated with S/G ratios in the lignins; however, γ-acylation was inversely correlated to the ratio between β-β and β-O-4 side chains in these lignin fractions. Moreover, a flavonoid compound (tricin) was also detected in the MWLS but not in MWLP. The two MWLs are very similar in terms of molecular weights and the contents of OHphen and OHaliph.

La surexploitation des ressources de la planète est aujourd’hui une problématique de premier ordre, et fait du remplacement des sources non renouvelables, d'énergie et de matières premières, l’un des défis majeurs du XXIe siècle. Dans cet objectif, les lignines, par leur disponibilité et leur biocompatibilité, apparaissent comme l’une des alternatives aux ressources fossiles. C’est dans ce contexte que le Laboratoire PEIRENE a décidé de mener ce travail de thèse portant sur le développement de nouveaux matériaux photosensibles à base de lignines modifiées. Dans ce but, trois lignines d’origines différentes ont été acétylées. Leur étude par spectroscopie RPE a révélé que le blocage de leurs fonctions antioxydantes augmente considérablement la quantité d’espèces réactives de l’oxygène qu’elles sont capables de générer sous irradiation lumineuse, permettant ainsi d’envisager l’utilisation de ce biopolymère modifié dans de nombreux domaines tels que le traitement photodynamique antimicrobien. Afin de les rendre hydrodispersibles et d’élargir ainsi leur champ d’applications, ces matériaux aux propriétés prometteuses ont été mis sous forme de nanoparticules puis, leur comportement photosensible a été lui aussi évalué par spectroscopie RPE. Il a ainsi été démontré qu’une fois dispersées dans l’eau sous la forme de nanoparticules, les lignines acétylées étaient toujours capables de produire de l’oxygène singulet sous irradiation lumineuse. Cette activité, qui n’a pas encore été reportée dans la littérature à notre connaissance, reste cependant assez restreinte et nécessite donc d’être améliorée. Afin d’élargir le domaine du spectre solaire permettant leur activation, un photosensibilisateur a par ailleurs été associé à ces nano-objets par encapsulation et par greffage covalent. L’ensemble des résultats découlant de ces travaux permettent d’envisager le développement de systèmes à base de nanoparticules de lignines acétylées dans de nombreux domaines, notamment pharmaceutique et phytosanitaire
The overexploitation of the planet's resources is nowadays a major problem and makes the replacement of non-renewable sources of energy and raw materials, one of the major challenges of the XXIe century. For this purpose, lignins, by their availability and their biocompatibility, appear as one of the alternatives to fossil resourcesIn this context, the PEIRENE Laboratory decided to carry out this PhD work on the development of new photosensitive materials based on modified lignins. For this purpose, three lignins from different origin were acetylated. Their study by EPR spectroscopy revealed that blocking their antioxidant functions considerably increases the quantity of reactive oxygen species they are able to generate under light irradiation. Thus it is possible to envisage the use of this modified biopolymer in many areas such as antimicrobial photodynamic therapy. In order to make them water-dispersible and thus to widen their field of applications, these materials with promising properties were put in the form of nanoparticles. Their photosensitive behavior has been also valuated by EPR spectroscopy. It has been demonstrated that once dispersed in water in the form of nanoparticles, the acetylated lignins were still capable of producing singlet oxygen under light irradiation. This activity, which has not yet been reported in the literature to our knowledge, however, remains quite limited and therefore needs to be improved. In order to widen the range of the solar spectrum allowing their activation, a photosensitizer has also been associated with these nano-objects by encapsulation and covalent grafting. The results of these studies make possible to envisage the development of systems based on acetylated lignins nanoparticles in in many field, in particular pharmaceutical and phytosanitary

Lignin is the second most abundant natural polymeric carbon source on earth after cellulose. It is a plant-originated polymer with three-dimensional network of dimethoxylated (syringyl), monomethoxylated (guaiacyl), and non-methoxylated (phydroxyphenyl) phenylpropanoid and acetylated units. The structural complexity and insolubility of lignin make it highly recalcitrant for degradation. Its biological degradation is critical to the global carbon cycle. Bioligninolysis involves application of microorganisms and their enzymes in degradation of lignin whichprovide environmental friendly technology for various industrial applications. As a major repository of aromatic chemical structures, lignin bears paramount significance for its removal from woody plants/lignocellulosic material, owing to potential application of bioligninolytic systems on commercial scale. This chapter provides an overview of microbial ligninolysis and its role in carbon cycling, various industrial process and pollution abatement for natural ecosystem management.

Lignin is the second most abundant natural polymeric carbon source on earth after cellulose. It is a plant-originated polymer with three-dimensional network of dimethoxylated (syringyl), monomethoxylated (guaiacyl), and non-methoxylated (phydroxyphenyl) phenylpropanoid and acetylated units. The structural complexity and insolubility of lignin make it highly recalcitrant for degradation. Its biological degradation is critical to the global carbon cycle. Bioligninolysis involves application of microorganisms and their enzymes in degradation of lignin whichprovide environmental friendly technology for various industrial applications. As a major repository of aromatic chemical structures, lignin bears paramount significance for its removal from woody plants/lignocellulosic material, owing to potential application of bioligninolytic systems on commercial scale. This chapter provides an overview of microbial ligninolysis and its role in carbon cycling, various industrial process and pollution abatement for natural ecosystem management.