Contribution to the Modification and Characterization of Different Types of Lignins (original) (raw)
Related papers
Chemical Modification and Characterization of Straw Lignin
Cellulose Chemistry and Technology, 2009
This work aims at describing the modification and characterization of lignin separated from annual plants (wheat straw) by their delignification through the alkaline method. The lignin has been subjected to the hydroxymethylation reaction, for introducing hydroxyl groups into its structure, thus assuring a more complete exploitation of this natural aromatic polymer. Chemical and spectral analyses (FTIR, UV-VIS, fluorescence, HPLC), and thermal stability characterization (TG, DTG) have been carried out to evidence the transformations occurring in the lignin macromolecule. The experimental data show that the hydroxymethylation reaction induces the modification of lignin functionality and polymolecularity. Further, the properties of modified lignin were demonstrated in experiments on wood bioprotection.
Cellulose Chemistry and Technology
This paper aims at the synthesis and chemical and spectral characterization of lignins from annual plants (L1-lignin from wheat straw, and L2-lignin from grass), modified by hydroxymethylation with formaldehyde in alkaline environment. The derivatives synthesized by this reaction were characterized by the introduced functional groups, which has been related to the consumption of formaldehyde under different conditions. Subsequently, additional information on the changes has been obtained by spectral studies (FTIR, 1 H NMR) and high performance steric exclusion chromatography (HPSEC). Studies have revealed some functional changes, related to both different reactivity of lignins and reaction conditions.
Physicochemical Characterisation of Technical Lignins for Their Potential Valorisation
Waste and Biomass Valorization, 2016
Lignin, the second most abundant natural polymer, has emerged as a potential alternative material to petroleum-based chemicals and renewable resource for the production of diverse forms of aromatics, biofuels, and biobased materials. Thus, it is becoming important to understand its structure and properties to provide key features and insights for better/efficient lignin valorisation. In this work, the physicochemical characterisation of two types of industrial (technical) lignins, namely LignoBoost lignin and alkali-treated lignin was performed. Characterisation has been conducted using Brunauer-Emmett-Teller N 2 adsorption, particle size distribution, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, gel permeation chromatography, and thermogravimetric analysis. It was found that the pretreatment severity considerably influenced the lignin composition and functional properties. The measured physicochemical properties helped in proposing potential valorisation routes for these lignins in the context of a biorefinery, focusing on their depolymerisation and subsequent biological conversion to value-added chemicals and fuels.
Bioresources
Corn stover and rice straw lignin samples received from ethanol pilot plants, along with softwood kraft lignin samples, were characterized using pyrolysis GC-MS, 13 C CP/MAS NMR spectroscopy, and permanganate oxidation degradation. The lignins were then esterified using 1-methylimidazole as a catalyst in a pyridine-free reaction, and the thermal properties of the products were evaluated. Solid state NMR showed the rice straw lignin contained 18% residual polysaccharides. Pyrolysis GC-MS showed the softwood kraft, corn stover, and rice straw lignins to be G-type, H/G/S-type, and G/S-type, respectively. However, some discrepancy was apparent between the pyrolysis and permanganate oxidation studies as to the ratios of the monomeric makeup of the lignins. The kraft and rice straw lignins were determined to have high degrees of condensation, while the corn stover lignin was uncondensed. Little to no increase in solubility was noticed for corn stover or rice straw lignin esters in organic solvents. Glass transition temperatures (T g) of the lignin derivatives were determined by a combination of differential scanning calorimetry, dynamic mechanical analysis, and parallel plate rheometry.
Lignin is the most abundant natural source of renewable aromatic units and therefore, detail characteri-sation to unveil its chemical properties is a critical step for its utilisation. Nine black liquor samples from different plant origins namely sugarcane bagasse, Eucalyptus grandis, and Pinus gregii extracted from the Kraft, soda, soda-anthraquinone and sulphite pulping processes were considered. After lignin purification, when applicable, the samples were characterised by several common methods (wet chemical methods, Fourier Transformed Infra-Red spectroscopy, Gel Permeation Chromatography). Lignin monomer composition (H:G:S) was determined by thioacidolysis as well as a new pyrolysis method based on the use of an analytical setup which couples Thermo Gravimetric Analysis (TGA) for lignin devolatilisation, the capture of released volatile compounds in thermal desorption (TD) tubes, and the quantification of the captured phenols by TD-GC–MS (gas chromatography–mass spectroscopy). The TGA-TD-GC–MS, with the use of internal calibration, allowed the quantification of 5.5–12.9 wt.% of monomeric products based on dry weight of purified lignin. Pyrolysis of sugarcane lignin resulted in significant yield of furfural, which was explained by the conversion of residual sugar. Pyrolysis of pine lignin gave the lowest yield of syringyl-type phenols, which was consistent with characterisation results (low methoxy content and absence of FT-IR band characteristic of syringyl unit). Pyrolysis method had the advantage to break different types of chemical bonds, which is likely to give a product distribution more representative of the lignin. With TGA-TD-GC–MS the monomer proportion for purified lignin from the same plant species were found to be very comparable (deviation lower than 10% for each unit). Compared to thioacidolysis (known to be selective towards bond cleavage and suspected to overestimate S content), TGA-TD-GC–MS gave lower S/G ratio. The TGA-TD-GC–MS method has demonstrated to be a good alternative technique to study the H:G:S proportions of lignins with low ash content (<5%).
The potential of organosolv and kraft eucalyptus and spruce lignin as feedstock for polymeric materials and biofuel applications was assessed. Proximate analysis was used to predict the heating values and char formation. Chemical modification, based on the esterification reaction with methacryloyl chloride, was applied to introduce vinyl groups into the lignin macromolecules for enhanced reactivity. Kraft eucalyptus and spruce lignins had a more condensed structure than organosolv lignins, which resulted in greater thermal stability for these lignins. For different species within the same process, the thermal parameters showed a correlation with certain structural and compositional parameters (ash and sugars content, molecular weight and degree of condensation). Organosolv spruce lignin produced the highest heating value of 24 MJ/Kg, which is suitable for biofuel applications. The content of phenolic OH groups was higher for kraft lignins and especially higher for softwood lignins, both organosolv and kraft. The degree of methacrylation, estimated from the content of vinyl groups per C9 lignin unit, was significantly greater for organosolv lignins than for kraft lignins despite the higher OH-groups content in the latter.
Analytical methods for lignin characterization. II. Spectroscopic studies
Cellulose chemistry and technology, 2006
Lignin' characterisation is a very difficult task, if considering its diversity with respect to both origin and method of separation. The heterogeneity of lignin is caused by variations in polymer's composition, size, crosslinking, functional groups, and linkage type between the phenyl propane monomers (p -hydroxyl phenyl, guaiacyl and syringyl units). The elaboration of well-defined analytical methods for lignin characterization is very important for its industrial applications as a raw material. Two groups of lignin from woody species and annual fibre crops have been studied by FT-IR, UV, fluorescence and 13 C NMR spectroscopy. The relative content of the different functional groups (p -hydroxy phenyl, guaiacyl and syringyl units) was appreciated by normalised intensities and deconvolution of the spectral bands. Correlation of the results provided by these methods permits differentiation between the structural characteristics of two lignin groups from the viewpoint of their particularities.
Physico-Chemical and Thermal Characterization of Alkali-Soluble Lignins from Wheat Straw
Polymer Journal, 1998
Four alkali-soluble lignin fractions were extracted from dewaxed wheat straw with 3% sodium hydroxide at 45°C for 2, 5, 12, and 15 h, respectively. The pure alkali-soluble lignin preparations LA were obtained by using a two step precipitation method instead of the traditional ether precipitation procedure. The physico-chemical properties and structural features of the isolated pure lignin fractions were characterized by UV, FT-IR, 13 C NMR spectroscopy, and thermal analysis. The lignin in fraction LA-I is mainly composed of /J-O-4 ether bonds. The less common /J-5 and /J-/J carbon-<:arbon linkages are also present in the lignin structural units. The results obtained showed that the lignin fractions appeared to be strongly associated to hydroxycinnamic acids such as p-coumaric and ferulic acids and glucuronic acid or 4-O-methylglucuronic acid.