Effect of pH on lignin analysis by Raman spectroscopy

Holzforschung ◽  
2012 ◽  
Vol 66 (4) ◽  
Author(s):  
Elina Warsta ◽  
Anni Lähdetie ◽  
Anna-Stiina Jääskeläinen ◽  
Tapani Vuorinen
Keyword(s):  
Raman Spectroscopy ◽  
Model Compound ◽  
Lignin Content ◽  
Raman Band ◽  
Band Intensity ◽  
Hydroxyl Groups ◽  
Model Compounds ◽  
Band Shift ◽  
Lignin Model ◽  
Ultraviolet Resonance Raman

Abstract Ultraviolet resonance Raman (UVRR) spectroscopy is a powerful tool for structural lignin analysis in situ: modification or isolation of lignin from biomass is not necessary. UVRR spectroscopy is equally applicable for samples with high lignin content and those with very low lignin content. Monomeric phenolic lignin model compounds and wood pulp samples have been studied at neutral and alkaline pH with UVRR spectroscopy. Concentration of guaiacol correlated well with the relative Raman band intensity, which indicates that lignin-containing solutions can be quantitatively measured with UVRR spectroscopy. A change in pH induced a recordable shift in the aromatic band position in the spectra, which was 25–35 cm-1 with phenolic model compounds without para substitution, 8–12 cm-1 with phenolic model compounds with para substitution, and about 2–7 cm-1 with pulp samples. No shift was detected with a non-phenolic model compound. Increasing the amount of phenolic hydroxyl groups increased the UVRR band shift in pulp samples. Additionally, increasing the pH enhanced the relative aromatic band intensity in the UVRR spectra in solution of the phenolic model compound. Accordingly, pH adjustment is relevant prior to any lignin analysis with Raman spectroscopy.

Convenient preparation of a β-O-4-type lignin model trimer via KOH-catalyzed hydroxymethylation and a new protection method

Holzforschung ◽  
2013 ◽  
Vol 67 (2) ◽  
pp. 129-136 ◽  
Author(s):  
Maarit Lahtinen ◽  
Anssi Haikarainen ◽  
Jussi Sipilä
Keyword(s):  
Model Compound ◽  
Catalytic Amount ◽  
Side Chain ◽  
Hydroxyl Groups ◽  
Chemical Behavior ◽  
Model Compounds ◽  
Protection Method ◽  
Convenient Synthesis ◽  
Lignin Model ◽  
Convenient Preparation

Abstract Lignin, as the second most abundant biopolymer on earth, is one of the targets for plant biorefinery studies. Its complex chemical behavior is frequently studied by dimeric, trimeric, etc. model compounds, preferably with a β-O-4-type structure. In the present study, a convenient synthesis of a β-O-4-type trimeric model compound possessing a free syringylic hydroxyl has been investigated. Two key modifications were in focus: (1) Protection of the aliphatic hydroxyl groups of the starting phenolic dimer prior to the SN2 displacement reaction before introducing the syringylic moiety with 2,2-dimethoxypropane. (2) The hydroxymethylation step to introduce the full side chain moiety. When this reaction was performed in dioxane/water in the presence of a catalytic amount of KOH instead of K2CO3, the formation of a side product via dehydration was markedly reduced. In addition, a convenient method for introducing an α,β-epoxide structure in acetophenone is recommended.

scholarly journals Study of the Reactivity of Lignin Model Compounds to Fluorobenzylation Using 13C and 19F NMR: Application to Lignin Phenolic Hydroxyl Group Quantification by 19F NMR

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3211
Author(s):  
Esakkiammal Sudha Esakkimuthu ◽  
Nathalie Marlin ◽  
Marie-Christine Brochier-Salon ◽  
Gérard Mortha
Keyword(s):  
Reaction Medium ◽  
19F Nmr ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Nmr Analysis ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Wide Range ◽  
Lignin Model ◽  
13C And 19F Nmr

Lignin is an aromatic biopolymer derived from lignocellulosic biomass. Providing a comprehensive structural analysis of lignin is the primary motivation for the quantification of various functional groups, with a view to valorizing lignin in a wide range of applications. This study investigated the lignin fluorobenzylation reaction and performed a subsequent 19F-NMR analysis to quantify hydroxyl groups, based on a work developed two decades ago by Barrelle et al. The objectives were to check the assignments proposed in this previous study and to examine the reactivity of various types of lignin hydroxyls with the derivatization agent. Selected lignin model compounds containing phenolic and aliphatic hydroxyls were subjected to the fluorobenzylation reaction, and the obtained reaction medium was analyzed by 13C and 19F NMR spectroscopy. The model compound results showed that phenolic hydroxyls were totally derivatized, whereas aliphatic hydroxyls underwent minimal conversion. They also confirmed that 19F NMR chemical shifts from −115 ppm to −117.3 ppm corresponded to phenolic groups. Then, a 19F NMR analysis was successfully applied to Organosolv commercial lignin after fluorobenzylation in order to quantify its phenolic group content; the values were found to be in the range of the reported values using other analytical techniques after lignin acetylation.

scholarly journals Effect of lignin structure on adsorbable organic halogens formation in chlorine dioxide bleaching

2019 ◽  
Vol 6 (2) ◽  
pp. 182024 ◽  
Author(s):  
Lisheng Shi ◽  
Jiayan Ge ◽  
Shuangxi Nie ◽  
Chengrong Qin ◽  
Shuangquan Yao
Keyword(s):  
Chlorine Dioxide ◽  
Model Compound ◽  
Pulp Bleaching ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Organic Halogens ◽  
Adsorbable Organic Halogens ◽  
Lignin Structure

Adsorbable organic halogens (AOX) are formed in pulp bleaching as a result of the reaction of residual lignin with chlorine dioxide. The natural structure of lignin is very complex and it tends to be damaged by various extraction methods. All the factors can affect the study about the mechanism of AOX formation in the reaction of lignin with chlorine dioxide. Lignin model compounds, with certain structures, can be used to study the role of different lignin structures on AOX formation. The effect of lignin structure on AOX formation was determined by reacting phenolic and non-phenolic lignin model compound with a chlorine dioxide solution. Vanillyl alcohol (VA) and veratryl alcohol (VE) were selected for the phenolic and non-phenolic lignin model compound, respectively. The pattern consumption of lignin model compounds suggests that both VA and VE began reacting with chlorine dioxide within 10 min and then gradually steadied. The volume of AOX produced by VE was significantly higher than that produced by VA for a given initial lignin model compound concentration. In a solution containing a combination of VA and VE in chlorine dioxide, VE was the dominant producer of AOX. This result indicates that the non-phenolic lignin structure was more easily chlorinated, while the phenolic lignin structure was mainly oxidized. In addition, AOX content produced in the combined experiments exceeded the total content of the two separate experiments. It suggested that the combination of phenolic and non-phenolic lignin structure can promote AOX formation.

Laser-induced fluorescence (LIF) of lignin and lignin model compounds in Raman spectroscopy

Holzforschung ◽  
2013 ◽  
Vol 67 (5) ◽  
pp. 531-538 ◽  
Author(s):  
Anni Lähdetie ◽  
Paula Nousiainen ◽  
Jussi Sipilä ◽  
Tarja Tamminen ◽  
Anna-Stiina Jääskeläinen
Keyword(s):  
Raman Spectroscopy ◽  
Structural Information ◽  
Laser Induced Fluorescence ◽  
Excitation Wavelength ◽  
Raman Signal ◽  
Model Compounds ◽  
Worst Case ◽  
Lignin Model Compounds ◽  
Key Factor ◽  
Lignin Model

Abstract Raman spectroscopy is a technique that provides structural information on lignin and other components of wood and pulp in situ. However, especially lignin-containing samples may produce laser-induced fluorescence (LIF) that overlaps with Raman bands. In the worst case, this background signal can overwhelm the weaker Raman signal completely. In this study, the LIF of lignin was investigated with the excitation wavelength 532 nm applied in Raman spectroscopy to clarify the correlations between lignin structure and LIF intensity. Raman spectroscopic analyses with lignin model compounds illustrated that the 5-5′ structures induce LIF. It was also shown that the intensity of LIF was significantly less intense when the 5-5′ model compound was structurally rigid (as in dibenzodioxocin) compared with the flexible simple counterpart. The comparison between the free phenolic model compounds with the methylated analogue showed that the presence of the free phenolic structure was not a prerequisite for LIF. It was thus concluded that the conformation of the molecule is the key factor with respect to fluorescence. The role of conformational aspects was further investigated by comparing wood with chemical pulps and isolated lignins.

Thermal stability of lignin in ground pulp (GP) and the effect of lignin modification on GP’s thermal stability: TGA experiments with dimeric lignin model compounds and milled wood lignins

Holzforschung ◽  
2019 ◽  
Vol 73 (5) ◽  
pp. 493-499 ◽  
Author(s):  
Daisuke Ando ◽  
Fumiaki Nakatsubo ◽  
Hiroyuki Yano
Keyword(s):  
Thermal Stability ◽  
Model Compound ◽  
Pinus Densiflora ◽  
Wood Fiber ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Oh Groups ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Thermal Stability Of

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.

Deformation Mechanisms in Natural Polymer Fibers and Composites

2001 ◽  
Vol 711 ◽  
Author(s):  
Robert J. Young ◽  
Stephen J. Eichhorn ◽  
J. Sirichaisit ◽  
Victoria L. Brookes
Keyword(s):  
Raman Spectroscopy ◽  
Tensile Deformation ◽  
Raman Band ◽  
Amorphous Structure ◽  
Polymer Chains ◽  
Polymer Fibers ◽  
Band Shift ◽  
Hemp Fibers ◽  
The Relationship ◽  
Molecular Deformation

ABSTRACTThe molecular deformation of both silkworm (Bombyx mori) and spider dragline (Nephila edulis) silks has been studied using a combination of mechanical testing and Raman spectroscopy. It was found that both materials have well-defined Raman spectra and that some of the bands in the spectra shift to lower wavenumber under the action of tensile stress or strain. The band shift was linearly dependent upon stress for both types of silk fiber for the 1085/1095 cm-1 band. This observation provides a unique insight into the effect of tensile deformation upon molecular structure and the relationship between structure and mechanical properties. The measurement of micromechanical deformation within samples of wood, flax and hemp fibers using Raman spectroscopy is also reported. Upon tensile deformation of the samples it was found that the characteristic Raman peak for cellulose, located at 1095 cm-1, shifted towards a lower wavenumber, indicating that the polymer chains within the cellulose were also being deformed. The magnitude of the shift with strain was found to be similar for all samples. No shift occurred of the peak that is characteristic of the non-load-bearing lignin (1600 cm-1) in the wood samples due to its amorphous structure. The similarities between the Raman band shifts in silk and cellulose are discussed.

Free radical reaction promoted by ionic liquid: a route for metal-free oxidation depolymerization of lignin model compound and lignin

2015 ◽  
Vol 51 (19) ◽  
pp. 4028-4031 ◽  
Author(s):  
Yingying Yang ◽  
Honglei Fan ◽  
Jinliang Song ◽  
Qinglei Meng ◽  
Huacong Zhou ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Model Compound ◽  
Radical Reaction ◽  
Free Radical Reaction ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Organosolv Lignin ◽  
Lignin Model ◽  
Free Oxidation

Ionic liquid can efficiently promote the transformation of lignin model compounds and organosolv lignin.

Removal of Phenolic Hydroxyl Groups in Lignin Model Compounds and Its Effect on Photostability

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 127-132 ◽  
Author(s):  
Thomas Q. Hu ◽  
Graham R. Cairns ◽  
Brian R. James
Keyword(s):  
Hydrogen Transfer ◽  
Phenolic Hydroxyl ◽  
Hydroxyl Groups ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Whatman Filter Paper ◽  
Elemental Analyses ◽  
Catalytic Hydrogen ◽  
Lignin Model ◽  
Phenolic Hydroxyl Groups

Summary The phenolic hydroxyl groups in the lignin model compounds, 2-methoxy-4-propylphenol and 4-hydroxy-3-methoxyacetophenone, were removed by first converting the hydroxyl groups to the trifluoromethanesulfonates (triflates) and then cleaving the triflate substituents via catalytic hydrogen transfer. The products, 1-methoxy-3-propylbenzene and 3-methoxyacetophenone, were characterized by 1H and 13C NMR, mass spectrometry and elemental analyses. The effect of the removal of the phenolic groups on the photostability of the model compounds was evaluated by impregnating the compounds into Whatman filter paper sheets, and subjecting them to an accelerated yellowing experiment in a UV chamber. The removal of the phenolic groups resulted in a significant yellowing inhibition, with a higher photostabilizing effect than methylation or acetylation of the hydroxyl, particularly for the model compound without an α-carbonyl group.

Fragmentation mechanism of the phenylcoumaran-type lignin model compound by ToF-SIMS

Holzforschung ◽  
2013 ◽  
Vol 67 (4) ◽  
pp. 365-370 ◽  
Author(s):  
Yasuyuki Matsushita ◽  
Kousuke Ioka ◽  
Kaori Saito ◽  
Ruka Takama ◽  
Dan Aoki ◽  
...  
Keyword(s):  
Model Compound ◽  
Furan Ring ◽  
Secondary Ion Mass Spectrometry ◽  
Model Compounds ◽  
Lignin Model Compound ◽  
Tof Sims ◽  
Secondary Ions ◽  
Lignin Model ◽  
The Common ◽  
Secondary Ion

Abstract The experiments with model compounds revealed that time-of-flight secondary ion mass spectrometry (ToF-SIMS) is able to split the common interunit linkages of lignin, except the 5-5 linkage. In a previous study, ToF-SIMS produced characteristic secondary ions with m/z 137 and 151 (C6-C1 fragments) from the phenylcoumaran-type lignin model compound, the benzofuran ring of which has a β-5 linkage and an α-O-4 linkage. However, it is still unclear whether the fragments are from ring A with the free phenolic OH as a result of the sole cleavage of the α-O-4 link by opening the furan ring or from ring B as a result of the β-5 cleavage. In this study, the phenylcoumaran-type lignin model compound and its deuterium- and/or 13C-labeled analogues were synthesized and analyzed by ToF-SIMS. It could be clarified that the β-5 linkage is not cleaved by ToF-SIMS.

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