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Polymers
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Lignin Polymers: Structures, Reactions and Applications
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Lignin Polymers: Structures, Reactions and Applications

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biomacromolecules, Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (25 July 2018)

Special Issue Editor

Prof. Dr. Fachuang Lu

E-Mail Website
Guest Editor
1. State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, 381 Wushan Rd., Tianhe District, Guangzhou 510640, China
2. Guangdong Engineering Research Center for Green Fine Chemicals, Guangzhou 510640, China
Interests: lignin chemistry and natural products; chemical conversion of carbohydrates; organic synthesis of model compounds of plant cell walls; chemistry involved in pulping and papermaking

Special Issue Information

Dear Colleagues,

Lignin polymer, commonly found in vascular plants, is one of the main components of plant cell walls. Lignin is the main natural resource of aromatic structures on Earth. Studies on lignin polymers have demonstrated that the amorphous and complex (heterogeneous) structures of lignins greatly limit their applications as functional materials or stock for chemical production. However, with the depletion of fossil oil and increased environmental concerns, renewable resources for energy and chemical production have attracted tremendous attentions from scientists and engineers. As a renewable aromatic polymer, lignin has been, for a long time, studied in terms of structures, reactivity and applications although few portions of lignins available from industry, mainly pulping mills, have been utilized for various applications.

The key for full and efficient utilization of lignins is that all aspects, including lignin structures from various origins, physicochemical properties, functionalities and reactivity, about lignins should be understood. Another important attribute related to lignin utilization comes from analytical methods essential for our understanding lignins and mechanism involved in various conversion processes. Therefore, it becomes necessary for better understanding and utilization of lignins that research efforts should focus on structural characterization, reactivity, and method development, as well as potential new applications.

In this Special Issue, it is intended to bring out updated knowledge and accomplishment related to various applications of lignins, and highlight progress in all aspects about lignin utilizations with emphasis on structures, reactivity and mechanism involved in various lignin conversion chemically and biologically.

Prof. Dr. Fachuang Lu
Guest Editor

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Keywords

  • Structural characterization
  • Isolation of lignins
  • Lignin conversion
  • Solvent systems for lignin dissolution
  • Analytical method development
  • Chemicals from lignin
  • Lignin based materials
  • Functionalities and reactivity
  • Biodegradation and environmental impact
  • New applications

Published Papers (15 papers)

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Research

14 pages, 2843 KiB  
Article
Synthesis of Nitrogen-Doped Lignin/DES Carbon Quantum Dots as a Fluorescent Probe for the Detection of Fe3+ Ions
by Xueqin Jiang, Yixin Shi, Xin Liu, Meng Wang, Pingping Song, Feng Xu and Xueming Zhang
Polymers 2018, 10(11), 1282; https://doi.org/10.3390/polym10111282 - 17 Nov 2018
Cited by 44 | Viewed by 6727
Abstract
Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials have extensive applications due to their excellent characteristics. In this work, we introduce a simple and green method to prepare nitrogen-doped lignin carbon quantum dots (N-L-CQDs) by using alkali lignin carbon sources [...] Read more.
Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials have extensive applications due to their excellent characteristics. In this work, we introduce a simple and green method to prepare nitrogen-doped lignin carbon quantum dots (N-L-CQDs) by using alkali lignin carbon sources and deep eutectic solvent (DES) as solution and nitrogen source. The physiochemical characterization results suggested that N-L-CQDs with diameters ranging from 4 to 12 nm were successfully synthesized. The optical properties data indicated that the as-prepared N-L-CQDs with a quantum yield of 7.95% exhibited excellent optoelectronic properties, excitation-dependent and pH stability. After that, we have investigated the N-L-CQDs used as fluorescent probes to detect iron ions, which suggested that the as-prepared N-L-CQDs exhibited excellent sensitivity and selectivity for Fe3+ with a detection limit of 0.44 μM. Besides, cytotoxicity of N-L-CQDs was also evaluated by MTT assay. These results demonstrated that the as-prepared N-L-CQDs with excellent properties have potential applications in environment and biomedicine. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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14 pages, 2033 KiB  
Article
Effects of Hydrothermal Pretreatment on the Structural Characteristics of Organosolv Lignin from Triarrhena lutarioriparia
by Tianying Chen, Zhiwen Li, Xueming Zhang, Douyong Min, Yuying Wu, Jialong Wen and Tongqi Yuan
Polymers 2018, 10(10), 1157; https://doi.org/10.3390/polym10101157 - 16 Oct 2018
Cited by 20 | Viewed by 3839
Abstract
The effects of hydrothermal pretreatment (170–180 °C, 30–60 min) on the structural characteristics of enzymatic and extracted lignin from Triarrhena lutarioriparia (TL) during the integrated delignification process have been comprehensively investigated. Ion chromatography and NMR characterization showed that liquid products after [...] Read more.
The effects of hydrothermal pretreatment (170–180 °C, 30–60 min) on the structural characteristics of enzymatic and extracted lignin from Triarrhena lutarioriparia (TL) during the integrated delignification process have been comprehensively investigated. Ion chromatography and NMR characterization showed that liquid products after mild hydrothermal process (170 °C, 30 min) were mainly composed of xylooligosaccharide (XOS) with different degrees of polymerization (DP ≥ 2). In addition, the structural changes of lignin during hydrothermal pretreatment and organic acid delignification process have been demonstrated by quantitative 2D heteronuclear single quantum coherence (2D-HSQC) and 31P-NMR techniques. Results showed that the structural changes of lignin (e.g., cleavage of β-O-4 linkages) induced by the hydrothermal pretreatment will facilitate the subsequent organic acid delignification process, and acetylated lignin could be obtained with a considerable yield, which can be used in lignin-based composite and candidate feedstock for catalytic upgrading of lignin. In short, the proposed process facilitates the producing of XOS and acetylated lignin for lignin valorization. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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15 pages, 2150 KiB  
Article
Study on the Effect of 1-Butanol Soluble Lignin on Temperature-Sensitive Gel
by Pan Jiang, Yi Cheng, Sheng Yu, Jie Lu and Haisong Wang
Polymers 2018, 10(10), 1109; https://doi.org/10.3390/polym10101109 - 08 Oct 2018
Cited by 14 | Viewed by 3641
Abstract
A protocol for the fractionation of lignin with 1-butanol as solvent has been proposed in order to improve the utilization of industry alkali lignin. 1-butanol soluble lignin (BSL) was used as a building block for temperature-sensitive hydrogel with N-isopropylacrylamide (NIPAAm) through graft [...] Read more.
A protocol for the fractionation of lignin with 1-butanol as solvent has been proposed in order to improve the utilization of industry alkali lignin. 1-butanol soluble lignin (BSL) was used as a building block for temperature-sensitive hydrogel with N-isopropylacrylamide (NIPAAm) through graft polymerization. The result shows that 1-butanol fractionation is an effective method to improve the molecular weight homogeneity of lignin (PDI, 2.5 to 1.83) and increase the hydroxyl group content (0.585–1.793 mmol/g). The incorporation of BSL into the temperature-sensitive hydrogel can enhance the thermal stability and increase the hydrophobicity of the gel, which leads to a decrease in lower critical solution temperature (LCST). In addition, the compression strength, swelling ratio, and pore size of the gel can be adjusted by the dosage of lignin. This stimuli-responsive gel, with an LCST around 32 °C, is expected to be applied in the agricultural field as a pesticide carrier by stimulating release and absorption properties based on the change in natural environmental temperature. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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11 pages, 2437 KiB  
Article
High-Efficient and Recyclable Magnetic Separable Catalyst for Catalytic Hydrogenolysis of β-O-4 Linkage in Lignin
by Jingtao Huang, Chengke Zhao and Fachuang Lu
Polymers 2018, 10(10), 1077; https://doi.org/10.3390/polym10101077 - 28 Sep 2018
Cited by 7 | Viewed by 3432
Abstract
Lignin is recognized as a good sustainable material because of its great abundance and potential applications. At present, lignin hydrogenolysis is considered as a potential but challenging way to produce low-molecular-mass aromatic chemicals. The most common linkage between the structural units of lignin [...] Read more.
Lignin is recognized as a good sustainable material because of its great abundance and potential applications. At present, lignin hydrogenolysis is considered as a potential but challenging way to produce low-molecular-mass aromatic chemicals. The most common linkage between the structural units of lignin polymer is the β-O-4 aryl ether, which are primary or even only target chemical bonds for many degradation processes. Herein, a Pd-Fe3O4 composite was synthesized for catalytic hydrogenolysis of β-O-4 bond in lignin. The synthesized catalyst was characterized by XRD, XPS, and SEM and the lignin depolymerization products were analyzed by GC-MS. The catalyst showed good catalytic performance during the hydrogenolysis process, lignin dimer was degraded into monomers completely and a high yield of monomers was obtained by the hydrogenolysis of bagasse lignin. More importantly, the magnetic catalyst was separated conveniently by magnet after reaction and remained highly catalytically efficient after being reused for five times. This work has demonstrated an efficient & recyclable catalyst for the cleavage of the β-O-4 bond in lignin providing an alternative way to make better use of lignins. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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15 pages, 6034 KiB  
Article
Bioinspired Engineering towards Tailoring Advanced Lignin/Rubber Elastomers
by Haixu Wang, Weifeng Liu, Jinhao Huang, Dongjie Yang and Xueqing Qiu
Polymers 2018, 10(9), 1033; https://doi.org/10.3390/polym10091033 - 18 Sep 2018
Cited by 45 | Viewed by 6536
Abstract
The pursuit of high volume and high value-added applications for lignin has been a long-term challenge. In this work, inspired by the energy sacrificial mechanism from biological materials, we developed high-performance lignin/carbon black (CB)/nitrile rubber (NBR) elastomers by constructing a dual-crosslinking network consisting [...] Read more.
The pursuit of high volume and high value-added applications for lignin has been a long-term challenge. In this work, inspired by the energy sacrificial mechanism from biological materials, we developed high-performance lignin/carbon black (CB)/nitrile rubber (NBR) elastomers by constructing a dual-crosslinking network consisting of sulfur covalent bonds and dynamic coordination sacrificial bonds. Lignin was not only used for the substitution of half mass of CB in the NBR elastomer but also served as natural ligands for the Zn-based coordination bonds, providing a significant synergistic coordination enhancement effect. The mechanical performance of the elastomers can be easily manipulated by adjusting the proportion of non-permanent coordination bonds and permanent covalent bonds. Lignin/CB/NBR elastomers with a higher strength and modulus than CB-filled elastomers were obtained while maintaining excellent elasticity. The thermal stability and the high-temperature oil resistance of NBR elastomers were also improved by incorporation of lignin and metal coordination bonds. Overall, this work inspires a new solution for the design of high-performance lignin/rubber elastomers with a high lignin loading content. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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12 pages, 3020 KiB  
Article
Preparation of a Low Reducing Effect Sulfonated Alkali Lignin and Application as Dye Dispersant
by Yanlin Qin, Xuliang Lin, Yaoqin Lu, Siyuan Wu, Dongjie Yang, Xueqing Qiu, Yanxiong Fang and Tiejun Wang
Polymers 2018, 10(9), 982; https://doi.org/10.3390/polym10090982 - 03 Sep 2018
Cited by 17 | Viewed by 5928
Abstract
A novel grafting hydroxypropyl sulfonated and blocking condensed lignin (GSBAL) dye dispersant was prepared based on alkali lignin (AL) by sulfonation and etherification reactions. The significant increase in the sulfonic group content and the molecular weight endow GSBAL with excellent dispersity and stability [...] Read more.
A novel grafting hydroxypropyl sulfonated and blocking condensed lignin (GSBAL) dye dispersant was prepared based on alkali lignin (AL) by sulfonation and etherification reactions. The significant increase in the sulfonic group content and the molecular weight endow GSBAL with excellent dispersity and stability at high temperatures. More importantly, the unfavorable property of the reducing effect of AL was largely reduced since over 80% of the phenolic hydroxyl groups were blocked. The functional azo groups in the dye could be mostly retained. The reducing rate of dye with GSBAL was decreased to 6.54% (25 °C), much lower than 18.62% for sulfomethylated alkali lignin (SAL) and 15.73% for sodium lignosulfonate (NaLS). The dispersity and exhaustion of the dye bath with GSBAL dispersant was significantly improved compared with that of a dye bath with SAL and NaLS. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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11 pages, 2236 KiB  
Article
Lignin Structure and Solvent Effects on the Selective Removal of Condensed Units and Enrichment of S-Type Lignin
by Si Gao, Ji Zhao, Xing Wang, Yanzhu Guo, Ying Han and Jinghui Zhou
Polymers 2018, 10(9), 967; https://doi.org/10.3390/polym10090967 - 01 Sep 2018
Cited by 28 | Viewed by 4205
Abstract
This study focused on the structural differences of lignin after pyridine–acetic acid–water (PAW) and dioxane–acidic water (DAW) purification processes. These structural differences included the S/G ratio, condensed structure, weight-average (MW) molecular weights, β-O-4 linkages and sugar content. The chemical structure of [...] Read more.
This study focused on the structural differences of lignin after pyridine–acetic acid–water (PAW) and dioxane–acidic water (DAW) purification processes. These structural differences included the S/G ratio, condensed structure, weight-average (MW) molecular weights, β-O-4 linkages and sugar content. The chemical structure of the isolated crude lignin (CL), PAW purified lignin (PPL) and DAW purified lignin (DPL) was elucidated using quantitative 13C NMR, 2D-HSQC NMR spectra, thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The results showed that the PPL fractions contain fewer condensed structures, higher S/G ratios, more β-O-4 linkages, higher average MW and lower thermal degradation properties compared to the CL and DPL fractions. Furthermore, the PAW process was more selective in removing condensed units and enriching S-type lignin from CL compared to the DAW process. These results provide valuable information for understanding which purification process is more suitable to be applied for lignin. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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6 pages, 6092 KiB  
Communication
Elucidating Tricin-Lignin Structures: Assigning Correlations in HSQC Spectra of Monocot Lignins
by Wu Lan, Fengxia Yue, Jorge Rencoret, José Carlos Del Río, Wout Boerjan, Fachuang Lu and John Ralph
Polymers 2018, 10(8), 916; https://doi.org/10.3390/polym10080916 - 15 Aug 2018
Cited by 30 | Viewed by 6416
Abstract
Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one] is a flavone that has been found to be incorporated in grass lignin polymers via 4′–O–β coupling. Herein, we investigated the tricin-lignin structure using nuclear magnetic resonance (NMR) methods by comparing the 1H–13C heteronuclear correlation (HSQC) NMR spectra of the isolated [...] Read more.
Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one] is a flavone that has been found to be incorporated in grass lignin polymers via 4′–O–β coupling. Herein, we investigated the tricin-lignin structure using nuclear magnetic resonance (NMR) methods by comparing the 1H–13C heteronuclear correlation (HSQC) NMR spectra of the isolated lignin with a series of dimeric and trimeric tricin-4′–O–β-ether model compounds. Results showed that the tricin moiety significantly affects the chemical shift of the Cβ/Hβ of 4′–O–β unit, producing peaks at around δC/δH 82.5–83.5/4.15–4.45, that differ from the Cβ/Hβ correlations from normal 4–O–β units formed solely by monolignols, and that have to date been unassigned. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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14 pages, 3761 KiB  
Article
Acylation of Lignin with Different Acylating Agents by Mechanical Activation-Assisted Solid Phase Synthesis: Preparation and Properties
by Xiaohong Zhao, Yanjuan Zhang, Mei Yang, Zuqiang Huang, Huayu Hu, Aimin Huang and Zhenfei Feng
Polymers 2018, 10(8), 907; https://doi.org/10.3390/polym10080907 - 12 Aug 2018
Cited by 19 | Viewed by 4787
Abstract
Acylated lignins with substituents consisting of different lengths of carbon chains were prepared by a mechanical activation-assisted solid phase synthesis (MASPS) technology with a customized stirring ball mill as a reactor. The structures and properties were analyzed by UV/Vis, FTIR, NMR, SEM, DSC, [...] Read more.
Acylated lignins with substituents consisting of different lengths of carbon chains were prepared by a mechanical activation-assisted solid phase synthesis (MASPS) technology with a customized stirring ball mill as a reactor. The structures and properties were analyzed by UV/Vis, FTIR, NMR, SEM, DSC, and TG. The results showed that the acylated lignins were successfully prepared with either non-cyclic or cyclic anhydrides as the acylating agents. Both aliphatic hydroxyl and phenolic hydroxyl groups of lignin reacted with non-cyclic anhydrides, and different reactivity of acylating agents resulted in different relative contents of phenolic and aliphatic substituents in the products. The reactivity of the cyclic anhydrides was weaker than that of the non-cyclic anhydrides, and the reactivity of the acylating agents decreased with increasing carbon chain length and unsaturated bonds of acyl groups. All of the acylated lignins except maleylated lignin had a lower glass transition temperature (Tg) than the original lignin. The acylated lignins prepared with non-cyclic anhydrides had better thermal stability than original lignin, and the thermal stability increased, but Tg decreased with an increasing chain length of the acyl groups. The acylated lignins prepared with cyclic anhydrides had higher a Tg than those with non-cyclic anhydrides with the same carbon number, and the thermal stability was not obviously improved. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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11 pages, 1536 KiB  
Article
Characterization of Lignin Extracted from Willow by Deep Eutectic Solvent Treatments
by Gaojin Lyu, Tengfei Li, Xingxiang Ji, Guihua Yang, Yu Liu, Lucian A. Lucia and Jiachuan Chen
Polymers 2018, 10(8), 869; https://doi.org/10.3390/polym10080869 - 05 Aug 2018
Cited by 48 | Viewed by 8078
Abstract
Purity, morphology, and structural characterization of synthesized deep eutectic solvent (DES)-lignins (D6h, D9h, D12h, D18h, D24h) extracted from willow (Salix matsudana cv. Zhuliu) after treatment with a 1:10 molar ratio of choline [...] Read more.
Purity, morphology, and structural characterization of synthesized deep eutectic solvent (DES)-lignins (D6h, D9h, D12h, D18h, D24h) extracted from willow (Salix matsudana cv. Zhuliu) after treatment with a 1:10 molar ratio of choline chloride and lactic acid at 120 °C for 6, 9, 12, 18, and 24 h were carried out. The purity of DES-lignin was ~95.4%. The proportion of hydrogen (H) in DES-lignin samples increased from 4.22% to 6.90% with lignin extraction time. The DES-lignin samples had low number/weight average molecular weights (1348.1/1806.7 to 920.2/1042.5 g/mol, from D6h to D24h) and low particle sizes (702–400 nm). Atomic force microscopy (AFM) analysis demonstrated that DES-lignin nanoparticles had smooth surfaces and diameters of 200–420 nm. Syringyl (S) units were dominant, and total phenolic hydroxyl content and total hydroxyl content reached their highest values of 2.05 and 3.42 mmol·g−1 in D12h and D6h, respectively. β-Aryl ether (β-O-4) linkages were eliminated during DES treatment. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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12 pages, 1358 KiB  
Article
Preparation and Characterization of Softwood Kraft Lignin Copolymers as a Paper Strength Additive
by Zhongming Liu, Dingding Xu, Lei Xu, Fangong Kong, Shoujuan Wang and Guihua Yang
Polymers 2018, 10(7), 743; https://doi.org/10.3390/polym10070743 - 05 Jul 2018
Cited by 16 | Viewed by 3831
Abstract
Softwood kraft lignin is a renewable type of woody material that can be converted to value-added products, for example, as a paper strength additive in the paper industry. In this study, the monomers of methacryloxyethyltrimethyl ammonium chloride (DMC), acrylic acid (AA), and acrylamide [...] Read more.
Softwood kraft lignin is a renewable type of woody material that can be converted to value-added products, for example, as a paper strength additive in the paper industry. In this study, the monomers of methacryloxyethyltrimethyl ammonium chloride (DMC), acrylic acid (AA), and acrylamide (AM) were grafted on softwood kraft lignin (SKL) to prepare three different SKL copolymers. Fourier-transform infrared, proton nuclear magnetic resonance, charge density, elemental, and molecular weight analyses confirmed that the monomers were successfully grafted onto SKL. The grafting rates of SKL-DMC, SKL-AA, and SKL-AM copolymers were 80.35%, 82.70%, and 79.48%, respectively. The application of SKL copolymers as a paper additive for enhancing paper physical properties was studied. The results indicated that at a 2 wt % dosage of SKL copolymers, the increase in the physical properties of paper is maximum. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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14 pages, 3037 KiB  
Article
Thermal Decomposition of Kraft Lignin under Gas Atmospheres of Argon, Hydrogen, and Carbon Dioxide
by Qiangu Yan, Jinghao Li, Jilei Zhang and Zhiyong Cai
Polymers 2018, 10(7), 729; https://doi.org/10.3390/polym10070729 - 03 Jul 2018
Cited by 19 | Viewed by 4845
Abstract
The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO2, or H2) were analyzed and compared using a temperature-programmed decomposition-mass spectrometry (TPD-MS) system. Experimental results indicated that Ar atmosphere produced the highest yield of solid [...] Read more.
The behaviors of thermal decomposition of kraft lignin under three different gases (Ar, CO2, or H2) were analyzed and compared using a temperature-programmed decomposition-mass spectrometry (TPD-MS) system. Experimental results indicated that Ar atmosphere produced the highest yield of solid chars, while H2 atmosphere generated the highest yield of liquids and CO2 atmosphere had the highest yield of gases. TPD-MS results showed that H2 atmosphere was consumed at the temperature range from 205 to 810 °C and CO2 atmosphere was consumed at the temperature range from 185 to 1000 °C. The H2 promoted the cleavage of lignin side chains and significantly enhanced the formation of CH4, C6H6, HCHO, C6H5OH, CH3OH, and tars. The percentages of water in produced liquids were 90.1%, 85.3%, and 95.5% for Ar, H2, and CO2 as atmosphere, respectively. The H2 yielded more organic chemicals in produced liquids compared to the other two gases. The observed organic chemicals were mainly acetic acid, phenols, ketones, alcohols, aldehydes, and esters. BET surface areas of solid products were 11.3, 98.5, and 183.9 m2/g for Ar., H2, and CO2 as the atmosphere, respectively. C–H–O–N–S elemental and morphology analyses on solid products indicated that the lowest carbon content and the highest oxygen content were obtained if Ar atmosphere was used, while H2 and CO2 yielded more carbon in final solid products. Solid products obtained under CO2 or H2 atmosphere contained sphere-shaped nanoparticles. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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11 pages, 2744 KiB  
Article
Structural Characterization of Lignocresols from Transgenic and Wild-Type Switchgrass
by Hao Ren, Wenyuan Tian, Fan Shu, Dongliang Xu, Chunxiang Fu and Huamin Zhai
Polymers 2018, 10(7), 727; https://doi.org/10.3390/polym10070727 - 02 Jul 2018
Cited by 4 | Viewed by 2627
Abstract
Cafferic acid-O-methyltransferases (COMT) down-regulated transgenic and wild-type switchgrass were separated into lignocresols (LCs) and sugars by a phase separation method involving 72% sulfuric acid and cresol. The isolated LCs were characterized by FTIR, GPC, 1H NMR and 2D-HSQC to understand [...] Read more.
Cafferic acid-O-methyltransferases (COMT) down-regulated transgenic and wild-type switchgrass were separated into lignocresols (LCs) and sugars by a phase separation method involving 72% sulfuric acid and cresol. The isolated LCs were characterized by FTIR, GPC, 1H NMR and 2D-HSQC to understand potential structural modification caused by transgenic engineering lignin or phase separation treatment. No significant changes were found in terms of molecular weights and the amount of incorporated p-cresols between transgenic and wild-type switchgrass LCs. However, the compositions, ratios of syringyl (S) units to guaiacyl (G) units, were changed significantly leading to decrease in S units and increase in G units for transgenic switchgrass LC. The benzodioxane structures and 5-hydroxyguaiacyl units were observed in the 2D-HSQC implied that 5-hydroxyconiferyl alcohol was incorporated into lignin as a result of COMT-down-regulation in the transgenic process. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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14 pages, 4662 KiB  
Article
Modification of Alkali Lignin with Poly(Ethylene Glycol) Diglycidyl Ether to Be Used as a Thickener in Bio-Lubricant Formulations
by Esperanza Cortés-Triviño, Concepción Valencia, Miguel A. Delgado and José M. Franco
Polymers 2018, 10(6), 670; https://doi.org/10.3390/polym10060670 - 16 Jun 2018
Cited by 27 | Viewed by 5651
Abstract
Considerable efforts are currently being made by the academic community and industry, aiming to develop environmentally friendly lubricants with suitable technical features for their performance. In this context, lignin could be considered a promising candidate to be used as a bio-sourced thickening agent [...] Read more.
Considerable efforts are currently being made by the academic community and industry, aiming to develop environmentally friendly lubricants with suitable technical features for their performance. In this context, lignin could be considered a promising candidate to be used as a bio-sourced thickening agent to formulate eco-friendly lubricating greases. In this work, alkali lignin (AL) was chemically modified with poly(ethylene glycol) diglycidyl ether (PEGDE). Afterwards, the epoxidized lignin was properly dispersed in castor oil (CO) in order to obtain an oleogel for lubricant applications. The epoxidized lignins were characterized by means of epoxy index determination, thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The epoxide-functionalized lignin-based oleogels were analyzed from both rheological and tribological points of view. It was found that the viscosity, consistency and viscoelastic functions of these oleogels clearly increased with the epoxy index of the epoxide-modified lignin compound. Thermo-rheological characterization of these oleogels revealed a slight thermal dependence of the viscoelastic moduli below 100 °C, but a significant softening above that critical temperature. In general, these oleogels showed low values of the friction coefficient under the mixed lubrication regime as compared to the neat castor oil. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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10 pages, 8153 KiB  
Communication
Carbon-Based Nanomaterials from Biopolymer Lignin via Catalytic Thermal Treatment at 700 to 1000 °C
by Xuefeng Zhang, Qiangu Yan, Jinghao Li, I-Wei Chu, Hossein Toghiani, Zhiyong Cai and Jilei Zhang
Polymers 2018, 10(2), 183; https://doi.org/10.3390/polym10020183 - 13 Feb 2018
Cited by 29 | Viewed by 4238
Abstract
We report the preparation of carbon-based nanomaterials from biopolymer kraft lignin via an iron catalytic thermal treatment process. Both the carbonaceous gases and amorphous carbon (AC) from lignin thermal decomposition were found to have participated in the formation of graphitic-carbon-encapsulated iron nanoparticles (GCEINs). [...] Read more.
We report the preparation of carbon-based nanomaterials from biopolymer kraft lignin via an iron catalytic thermal treatment process. Both the carbonaceous gases and amorphous carbon (AC) from lignin thermal decomposition were found to have participated in the formation of graphitic-carbon-encapsulated iron nanoparticles (GCEINs). GCEINs originating from carbonaceous gases have thick-walled graphitic-carbon layers (10 to 50) and form at a temperature of 700 °C. By contrast, GCEINs from AC usually have thin-walled graphitic-carbon layers (1 to 3) and form at a temperature of at least 800 °C. Iron catalyst nanoparticles started their phase transition from α-Fe to γ-Fe at 700 °C, and then from γ-Fe to Fe3C at 1000 °C. Furthermore, we derived a formula to calculate the maximum number of graphitic-carbon layers formed on iron nanoparticles via the AC dissolution-precipitation mechanism. Full article
(This article belongs to the Special Issue Lignin Polymers: Structures, Reactions and Applications)
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