Molecules

Research

14 pages, 4760 KiB

Open AccessArticle

High Value Utilization of Waste Wood toward Porous and Lightweight Carbon Monolith with EMI Shielding, Heat Insulation and Mechanical Properties

by Xiaofan Ma, Xiaoshuai Han, Jiapeng Hu, Weisen Yang, Jingquan Han, Zhichao Lou, Chunmei Zhang and Shaohua Jiang

Molecules 2023, 28(6), 2482; https://doi.org/10.3390/molecules28062482 - 8 Mar 2023

Cited by 9 | Viewed by 2107

Abstract

With the increasing pollution of electromagnetic (EM) radiation, it is necessary to develop low-cost, renewable electromagnetic interference (EMI) shielding materials. Herein, wood-derived carbon (WC) materials for EMI shielding are prepared by one-step carbonization of renewable wood. With the increase in carbonization temperature, the [...] Read more.

With the increasing pollution of electromagnetic (EM) radiation, it is necessary to develop low-cost, renewable electromagnetic interference (EMI) shielding materials. Herein, wood-derived carbon (WC) materials for EMI shielding are prepared by one-step carbonization of renewable wood. With the increase in carbonization temperature, the conductivity and EMI performance of WC increase gradually. At the same carbonization temperature, the denser WC has better conductivity and higher EMI performance. In addition, due to the layered superimposed conductive channel structure, the WC in the vertical-section shows better EMI shielding performance than that in the cross-section. After excluding the influence of thickness and density, the specific EMI shielding effectiveness (SSE/t) value can be calculated to further optimize tree species. We further discuss the mechanism of the influence of the microstructure of WC on its EMI shielding properties. In addition, the lightweight WC EMI material also has good hydrophobicity and heat insulation properties, as well as good mechanical properties. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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17 pages, 4021 KiB

Open AccessArticle

Potential of Staphylea holocarpa Wood for Renewable Bioenergy

by Yiyang Li, Erdong Liu, Haiping Gu, Junwei Lou, Yafeng Yang, Longhai Ban, Wanxi Peng and Shengbo Ge

Molecules 2023, 28(1), 299; https://doi.org/10.3390/molecules28010299 - 30 Dec 2022

Viewed by 1817

Abstract

Energy is indispensable in human life and social development, but this has led to an overconsumption of non-renewable energy. Sustainable energy is needed to maintain the global energy balance. Lignocellulose from agriculture or forestry is often discarded or directly incinerated. It is abundantly [...] Read more.

Energy is indispensable in human life and social development, but this has led to an overconsumption of non-renewable energy. Sustainable energy is needed to maintain the global energy balance. Lignocellulose from agriculture or forestry is often discarded or directly incinerated. It is abundantly available to be discovered and studied as a biomass energy source. Therefore, this research uses Staphylea holocarpa wood as feedstock to evaluate its potential as energy source. We characterized Staphylea holocarpa wood by utilizing FT–IR, GC–MS, TGA, Py/GC–MS and NMR. The results showed that Staphylea holocarpa wood contained a large amount of oxygenated volatiles, indicating that it has the ability to act as biomass energy sources which can achieve green chemistry and sustainable development. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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14 pages, 2926 KiB

Open AccessArticle

Chemical and Mechanical Characterization of Licorice Root and Palm Leaf Waste Incorporated into Poly(urethane-acrylate) (PUA)

by Serena Gabrielli, Genny Pastore, Francesca Stella, Enrico Marcantoni, Fabrizio Sarasini, Jacopo Tirillò and Carlo Santulli

Molecules 2021, 26(24), 7682; https://doi.org/10.3390/molecules26247682 - 19 Dec 2021

Cited by 8 | Viewed by 3459

Abstract

A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and [...] Read more.

A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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16 pages, 3085 KiB

Open AccessArticle

Chemical Characterization of Kraft Lignin Prepared from Mixed Hardwoods

by Ji-Sun Mun, Justin Alfred Pe III and Sung-Phil Mun

Molecules 2021, 26(16), 4861; https://doi.org/10.3390/molecules26164861 - 11 Aug 2021

Cited by 22 | Viewed by 3981

Abstract

Chemical characterization of kraft lignin (KL) from mixed hardwoods (Acacia spp. from Vietnam and mixed hardwoods (mainly Quercus spp.) from Korea) was conducted for its future applications. To compare the structural changes that occurred in KL, two milled wood lignins (MWLs) were [...] Read more.

Chemical characterization of kraft lignin (KL) from mixed hardwoods (Acacia spp. from Vietnam and mixed hardwoods (mainly Quercus spp.) from Korea) was conducted for its future applications. To compare the structural changes that occurred in KL, two milled wood lignins (MWLs) were prepared from the same hardwood samples used in the production of KL. Elemental analysis showed that the MWL from acacia (MWL-aca) and mixed hardwood (MWL-mhw) had almost similar carbon content, methoxyl content, and C₉ formula. KL had high carbon content but low oxygen and methoxyl contents compared to MWLs. The C₉ formula of KL was determined to be C₉H_7.29O_2.26N_0.07S_0.12(OCH₃)_1.24. The M_w of KL and MWLs was about 3000 Da and 12,000–13,000 Da, respectively. The structural features of KL and MWLs were investigated by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectrometry (¹H, ¹³C NMR). The analyses indicated that KL underwent severe structural modifications, such as γ-carbon cleavage, demethylation, and polycondensation reactions during kraft pulping, which resulted in increased aromatic content and decreased aliphatic content. The main linkages in lignin, β-O-4 moieties, were hardly detected in the analysis as these linkages were extensively cleaved by nucleophilic attack of SH^- and OH^- during pulping. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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18 pages, 6063 KiB

Open AccessArticle

Lignin as a Partial Polyol Replacement in Polyurethane Flexible Foam

by Akash Gondaliya and Mojgan Nejad

Molecules 2021, 26(8), 2302; https://doi.org/10.3390/molecules26082302 - 15 Apr 2021

Cited by 34 | Viewed by 6775

Abstract

This study was focused on evaluating the suitability of a wide range of lignins, a natural polymer isolated from different plant sources and chemical extractions, in replacing 20 wt.% of petroleum-based polyol in the formulation of PU flexible foams. The main goal was [...] Read more.

This study was focused on evaluating the suitability of a wide range of lignins, a natural polymer isolated from different plant sources and chemical extractions, in replacing 20 wt.% of petroleum-based polyol in the formulation of PU flexible foams. The main goal was to investigate the effect of unmodified lignin incorporation on the foam’s structural, mechanical, and thermal properties. The hydroxyl contents of the commercial lignins were measured using phosphorus nuclear magnetic resonance (³¹P NMR) spectroscopy, molar mass distributions with gel permeation chromatography (GPC), and thermal properties with differential scanning calorimetry (DSC) techniques. The results showed that incorporating 20 wt.% lignin increased tensile, compression, tear propagation strengths, thermal stability, and the support factor of the developed PU flexible foams. Additionally, statistical analysis of the results showed that foam properties such as density and compression force deflection were positively correlated with lignin’s total hydroxyl content. Studying correlations between lignin properties and the performance of the developed lignin-based PU foams showed that lignins with low hydroxyl content, high flexibility (low T_g), and high solubility in the co-polyol are better candidates for partially substituting petroleum-based polyols in the formulation of flexible PU foams intended for the automotive applications. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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14 pages, 3063 KiB

Open AccessArticle

Binderless, All-Lignin Briquette from Black Liquor Waste: Isolation, Purification, and Characterization

by Yati Mardiyati, Emia Yoseva Tarigan, Pandji Prawisudha, Silvia Mar’atus Shoimah, Raden Reza Rizkiansyah and Steven Steven

Molecules 2021, 26(3), 650; https://doi.org/10.3390/molecules26030650 - 27 Jan 2021

Cited by 7 | Viewed by 3594

Abstract

Lignin isolated from black liquor waste was studied in this research to be utilized as binderless, all-lignin briquette, with a calorific value in the range of 5670–5876 kcal/kg. Isolation of lignin from black liquor was conducted using the acid precipitation method. Sulfuric acid, [...] Read more.

Lignin isolated from black liquor waste was studied in this research to be utilized as binderless, all-lignin briquette, with a calorific value in the range of 5670–5876 kcal/kg. Isolation of lignin from black liquor was conducted using the acid precipitation method. Sulfuric acid, citric acid, and acetic acid were used to maintain the pH level, which varied from 5 to 2 for the precipitation process. The influence of these isolation conditions on the characteristic of lignin and the properties of the resulted briquette was evaluated through the Klasson method, proximate analysis, ultimate analysis, Fourier Transform Infrared (FTIR), adiabatic bomb calorimeter, density measurement, and Drop Shatter Index (DSI) testing. The finding showed that the lignin isolated using citric acid maintained to pH 3 resulted in briquette with 72% fixed carbon content, excellent 99.7% DSI, and a calorific value equivalent to coal-based briquette. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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20 pages, 4062 KiB

Open AccessArticle

Flammability Tests and Investigations of Properties of Lignin-Containing Polymer Composites Based on Acrylates

by Beata Podkościelna, Krystyna Wnuczek, Marta Goliszek, Tomasz Klepka and Kamil Dziuba

Molecules 2020, 25(24), 5947; https://doi.org/10.3390/molecules25245947 - 15 Dec 2020

Cited by 18 | Viewed by 3270

Abstract

In this paper flammability tests and detailed investigations of lignin-containing polymer composites’ properties are presented. Composites were obtained using bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BPA.GDA), ethylene glycol dimethacrylate (EGDMA), and kraft lignin (lignin alkali, L) during UV curing. In order to evaluate [...] Read more.

In this paper flammability tests and detailed investigations of lignin-containing polymer composites’ properties are presented. Composites were obtained using bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BPA.GDA), ethylene glycol dimethacrylate (EGDMA), and kraft lignin (lignin alkali, L) during UV curing. In order to evaluate the influence of lignin modification and the addition of flame retardant compounds on the thermal resistance of the obtained biocomposites, flammability tests have been conducted. After the modification with phosphoric acid (V) lignin, as well as diethyl vinylphosphonate, were used as flame retardant additives. The changes in the chemical structures (ATR-FTIR), as well as the influence of the different additives on the hardness, thermal (TG) and mechanical properties were discussed in detail. The samples after the flammability test were also studied to assess their thermal destruction. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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25 pages, 4716 KiB

Open AccessArticle

i-Propylammonium Lead Chloride Based Perovskite Photocatalysts for Depolymerization of Lignin Under UV Light

by Samia Kausar, Ataf Ali Altaf, Muhammad Hamayun, Nasir Rasool, Mahwish Hadait, Arusa Akhtar, Shabbir Muhammad, Amin Badshah, Syed Adnan Ali Shah and Zainul Amiruddin Zakaria

Molecules 2020, 25(15), 3520; https://doi.org/10.3390/molecules25153520 - 31 Jul 2020

Cited by 12 | Viewed by 5061

Abstract

Lignin depolymerization for the purpose of synthesizing aromatic molecules is a growing focus of research to find alternative energy sources. In current studies, the photocatalytic depolymerization of lignin has been investigated by two new iso-propylamine-based lead chloride perovskite nanomaterials (SK9 and SK10 [...] Read more.

Lignin depolymerization for the purpose of synthesizing aromatic molecules is a growing focus of research to find alternative energy sources. In current studies, the photocatalytic depolymerization of lignin has been investigated by two new iso-propylamine-based lead chloride perovskite nanomaterials (SK9 and SK10), synthesized by the facile hydrothermal method. Characterization was done by Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), UV-Visible (UV-Vis), Photoluminescence (PL), and Fourier-Transform Infrared (FTIR) Spectroscopy and was used for the photocatalytic depolymerization of lignin under UV light. Lignin depolymerization was monitored by taking absorption spectra and catalytic paths studied by applying kinetic models. The %depolymerization was calculated for factors such as catalyst dose variation, initial concentration of lignin, and varying temperatures. Pseudo-second order was the best suited kinetic model, exhibiting a mechanism for lignin depolymerization that was chemically rate controlled. The activation energy (E_a) for the depolymerization reaction was found to be 15 kJ/mol, which is remarkably less than conventional depolymerization of the lignin, i.e., 59.75 kJ/mol, exhibiting significant catalytic efficiencies of synthesized perovskites. Products of lignin depolymerization obtained after photocatalytic activity at room temperature (20 °C) and at 90 °C were characterized by GC-MS analysis, indicating an increase in catalytic lignin depolymerization structural subunits into small monomeric functionalities at higher temperatures. Specifically, 2-methoxy-4-methylphenol (39%), benzene (17%), phenol (10%) and catechol (7%) were detected by GC-MS analysis of lignin depolymerization products. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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17 pages, 2000 KiB

Open AccessArticle

Epoxidation of Kraft Lignin as a Tool for Improving the Mechanical Properties of Epoxy Adhesive

by Julia R. Gouveia, Guilherme E. S. Garcia, Leonardo Dalseno Antonino, Lara B. Tavares and Demetrio J. dos Santos

Molecules 2020, 25(11), 2513; https://doi.org/10.3390/molecules25112513 - 28 May 2020

Cited by 63 | Viewed by 5916

Abstract

Owing to its chemical structure, wide availability and renewable nature, lignin is a promising candidate for the partial replacement of fossil-based raw material in the synthesis of epoxy resins. Its poor compatibility has been reported to be one of the main drawbacks in [...] Read more.

Owing to its chemical structure, wide availability and renewable nature, lignin is a promising candidate for the partial replacement of fossil-based raw material in the synthesis of epoxy resins. Its poor compatibility has been reported to be one of the main drawbacks in this domain. On the other hand, a well-established modification method for lignin epoxidation has been used for many years for the improvement of lignin compatibility. However, the extent of the effect of lignin epoxidation on the improvement of bio-based epoxy mechanical properties, applied as adhesives, is still an open question in the literature. In this context, a pristine and industrial grade kraft lignin (AKL) was reacted with epichlorohydrin to yield epoxidized lignin (E-AKL) in this work. Afterwards, AKL or E-AKL were separately blended with petroleum-based epoxy resin at 15 and 30 wt% and cured with a commercial amine. The adhesive curing kinetic was evaluated using a novel technique for thermal transition characterization, Temperature Modulated Optical Refractometry (TMOR); the results showed that the incorporation of AKL reduces the crosslinking rate, and that this effect is overcome by lignin modification. Mechanical tests revealed an improvement of impact and practical adhesion strength for samples containing 15 wt% of E-AKL. These results elucidate the effect of lignin epoxidation on the application of lignin-based epoxy adhesives, and might support the further development and application of these bio-based materials. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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19 pages, 3185 KiB

Open AccessArticle

Sustainable Process for the Depolymerization/Oxidation of Softwood and Hardwood Kraft Lignins Using Hydrogen Peroxide under Ambient Conditions

by Zaid Ahmad, Waleed Wafa Al Dajani, Michael Paleologou and Chunbao (Charles) Xu

Molecules 2020, 25(10), 2329; https://doi.org/10.3390/molecules25102329 - 16 May 2020

Cited by 36 | Viewed by 5353

Abstract

The present study demonstrated a sustainable and cost-effective approach to depolymerize/oxidize softwood (SW) and hardwood (HW) kraft lignins using concentrated hydrogen peroxide at temperatures ranging from 25 to 35 °C, in the absence of catalysts or organic solvents. The degree of lignin depolymerization [...] Read more.

The present study demonstrated a sustainable and cost-effective approach to depolymerize/oxidize softwood (SW) and hardwood (HW) kraft lignins using concentrated hydrogen peroxide at temperatures ranging from 25 to 35 °C, in the absence of catalysts or organic solvents. The degree of lignin depolymerization could be simply controlled by reaction time, and no further separation process was needed at the completion of the treatment. The obtained depolymerized lignin products were comprehensively characterized by GPC–UV, FTIR, ³¹P-NMR, TGA, Py-GC/MS and elemental analysis. The weight-average molecular weights (M_w) of the depolymerized lignins obtained from SW or HW lignin at a lignin/H₂O₂ mass ratio of 1:1 after treatment for 120 h at room temperature (≈25 °C) were approximately 1420 Da. The contents of carboxylic acid groups in the obtained depolymerized lignins were found to significantly increase compared with those of the untreated raw lignins. Moreover, the depolymerized lignin products had lower thermal decomposition temperatures than those of the raw lignins, as expected, owing to the greatly reduced M_w. These findings represent a novel solution to lignin depolymerization for the production of chemicals that can be utilized as a bio-substitute for petroleum-based polyols in polyurethane production. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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16 pages, 7053 KiB

Open AccessArticle

Effect of Solvents on Fe–Lignin Precursors for Production Graphene-Based Nanostructures

by Qiangu Yan and Zhiyong Cai

Molecules 2020, 25(9), 2167; https://doi.org/10.3390/molecules25092167 - 6 May 2020

Cited by 15 | Viewed by 3648

Abstract

Kraft lignin was catalytically graphitized to graphene-based nanostructures at high temperature under non-oxidative atmospheres. To obtain the best catalytic performance, a uniform catalyst–lignin mixture must be made by bonding transitional metal (M) ions to oxygen (O), sulfur (S) or nitrogen (N)-containing functional groups [...] Read more.

Kraft lignin was catalytically graphitized to graphene-based nanostructures at high temperature under non-oxidative atmospheres. To obtain the best catalytic performance, a uniform catalyst–lignin mixture must be made by bonding transitional metal (M) ions to oxygen (O), sulfur (S) or nitrogen (N)-containing functional groups in kraft lignin. One of the strategies is to dissolve or disperse kraft lignin in a suitable solvent, whereby the polymer chains in the condensed lignin molecules will be detangled and stretched out while the functional groups are solvated, and when mixing lignin solution with catalyst metal solution, the solvated metal ions in an aqueous solution can diffuse and migrate onto lignin chains to form M-O, M-S, or M-N bonds during the mixing process. Therefore, solvent effects are important in preparing M–lignin mixture for production of graphene-based nanostructures. Fe–lignin precursors were prepared by dissolving lignin with different solvents, including water, methanol, acetone, and tetrahydrofuran (THF). Solvent effects on the catalytic performance, size and morphology of graphene-based nanostructures were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), and nitrogen sorption measurements. The sizes, morphologies, and catalytic properties of the products obtained from Fe–lignin precursors are greatly influenced by the solvents used. It was found that Fe–lignin (THF) had the highest iron dispersion and the smallest iron particle size. Furthermore, Fe–lignin (THF) exhibited the best catalytic performance for graphitization of kraft lignin while the graphitization degree decreased in the order: Fe–lignin(THF) > Fe–lignin(Acetone) > Fe–lignin(methanol) > Fe–lignin(water). Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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16 pages, 2796 KiB

Open AccessArticle

Electrical and Optical Properties of Silicon Oxide Lignin Polylactide (SiO₂-L-PLA)

by Jacek Fal, Katarzyna Bulanda, Julian Traciak, Jolanta Sobczak, Rafał Kuzioła, Katarzyna Maria Grąz, Grzegorz Budzik, Mariusz Oleksy and Gaweł Żyła

Molecules 2020, 25(6), 1354; https://doi.org/10.3390/molecules25061354 - 16 Mar 2020

Cited by 9 | Viewed by 3704

Abstract

This paper presents a study on the electrical properties of new polylactide-based nanocomposites with the addition of silicon-dioxide–lignin nanoparticles and glycerine as a plasticizer. Four samples were prepared with nanoparticle mass fractions ranging between 0.01 to 0.15 (0.01, 0.05, 0.10, and 0.15), and [...] Read more.

This paper presents a study on the electrical properties of new polylactide-based nanocomposites with the addition of silicon-dioxide–lignin nanoparticles and glycerine as a plasticizer. Four samples were prepared with nanoparticle mass fractions ranging between 0.01 to 0.15 (0.01, 0.05, 0.10, and 0.15), and three samples were prepared without nanoparticle filler—unfilled and unprocessed polylactide, unfilled and processed polylactide, and polylactide with Fusabond and glycerine. All samples were manufactured using the melt mixing extrusion technique and injection molding. Only the unfilled and unprocessed PLA sample was directly prepared by injection molding. Dielectric properties were studied with broadband spectroscopy in a frequency range from 0.1 Hz to 1 MHz in 55 steps designed on a logarithmic scale and a temperature range from 293.15 to 333.15 K with a 5 K step. Optical properties of nanocomposites were measured with UV-VIS spectroscopy at wavelengths from 190 to 1100 nm. The experimental data show that the addition of silicon-dioxide–lignin and glycerine significantly affected the electrical properties of the studied nanocomposites based on polylactide. Permittivity and electrical conductivity show a significant increase with an increasing concentration of nanoparticle filler. The optical properties are also affected by nanofiller and cause an increase in absorbance as the number of silicon-dioxide–lignin nanoparticles increase. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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16 pages, 2878 KiB

Open AccessArticle

Functional MgO–Lignin Hybrids and Their Application as Fillers for Polypropylene Composites

by Aleksandra Grząbka-Zasadzińska, Łukasz Klapiszewski, Teofil Jesionowski and Sławomir Borysiak

Molecules 2020, 25(4), 864; https://doi.org/10.3390/molecules25040864 - 16 Feb 2020

Cited by 17 | Viewed by 3396

Abstract

Inorganic–organic hybrids are a group of materials that have recently become the subject of intense scientific research. They exhibit some of the specific properties of both highly durable inorganic materials (e.g., titanium dioxide, zinc) and organic products with divergent physicochemical traits (e.g., lignin, [...] Read more.

Inorganic–organic hybrids are a group of materials that have recently become the subject of intense scientific research. They exhibit some of the specific properties of both highly durable inorganic materials (e.g., titanium dioxide, zinc) and organic products with divergent physicochemical traits (e.g., lignin, chitin). This combination results in improved physicochemical, thermal or mechanical properties. Hybrids with defined characteristics can be used as fillers for polymer composites. In this study, three types of filler with different MgO/lignin ratio were used as fillers for polypropylene (PP). The effectiveness of MgO-lignin binding was confirmed using Fourier transform infrared spectroscopy. The fillers were also tested in terms of thermal stability, dispersive-morphological properties as well as porous structure. Polymer composites containing 3 wt.% of each filler were subjected to wide angle X-ray diffraction tests, differential scanning calorimetry and microscopic studies to define their structure, morphology and thermal properties. Additionally, tensile tests of the composites were performed. It was established that the composition of the filler has a significant influence on the crystallization of polypropylene—either spherulites or transcrystalline layers were formed. The value of Young’s modulus and tensile strength remained unaffected by filler type. However, composites with hybrid fillers exhibited lower elongation at break than unfilled polypropylene. Full article

(This article belongs to the Special Issue Lignin: From Nature to Advanced Materials)

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15 pages, 4064 KiB

Open AccessArticle

Lignin-Based Hybrid Admixtures and their Role in Cement Composite Fabrication

by Łukasz Klapiszewski, Izabela Klapiszewska, Agnieszka Ślosarczyk and Teofil Jesionowski

Molecules 2019, 24(19), 3544; https://doi.org/10.3390/molecules24193544 - 30 Sep 2019

Cited by 29 | Viewed by 3994

Abstract

In this study, a technology for obtaining functional inorganic-organic hybrid materials was designed using waste polymers of natural origin, i.e., kraft lignin and magnesium lignosulfonate, and alumina as an inorganic component. Al₂O₃-lignin and Al₂O₃-lignosulfonate systems [...] Read more.

In this study, a technology for obtaining functional inorganic-organic hybrid materials was designed using waste polymers of natural origin, i.e., kraft lignin and magnesium lignosulfonate, and alumina as an inorganic component. Al₂O₃-lignin and Al₂O₃-lignosulfonate systems were prepared by a mechanical method using a mortar grinder and a planetary ball mill, which made it possible to obtain products of adequate homogeneity in an efficient manner. This was confirmed by the use of Fourier transform infrared spectroscopy and thermogravimetric analysis. In the next step, the developed hybrid materials were used as functional admixtures in cement mixtures, thus contributing to the formation of a modern, sustainable building material. How the original components and hybrid materials affected the mechanical properties of the resulting mortars was investigated. The admixture of biopolymers, especially lignin, led to cement composites characterized by greater plasticity, while alumina improved their strength properties. It was confirmed that the system containing 0.5 wt.% of alumina-lignin material is the most suitable for application as a cement mortar admixture. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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15 pages, 3535 KiB

Open AccessArticle

Structural and Thermal Analysis of Softwood Lignins from a Pressurized Hot Water Extraction Biorefinery Process and Modified Derivatives

by Lucas Lagerquist, Andrey Pranovich, Ivan Sumerskii, Sebastian von Schoultz, Lari Vähäsalo, Stefan Willför and Patrik Eklund

Molecules 2019, 24(2), 335; https://doi.org/10.3390/molecules24020335 - 18 Jan 2019

Cited by 11 | Viewed by 4067

Abstract

In this work we have analyzed the pine and spruce softwood lignin fraction recovered from a novel pressurized hot water extraction pilot process. The lignin structure was characterized using multiple NMR techniques and the thermal properties were analyzed using thermal gravimetric analysis. Acetylated [...] Read more.

In this work we have analyzed the pine and spruce softwood lignin fraction recovered from a novel pressurized hot water extraction pilot process. The lignin structure was characterized using multiple NMR techniques and the thermal properties were analyzed using thermal gravimetric analysis. Acetylated and selectively methylated derivatives were prepared, and their structure and properties were analyzed and compared to the unmodified lignin. The lignin had relatively high molar weight and low PDI values and even less polydisperse fractions could be obtained by fractionation based on solubility in i-PrOH. Condensation, especially at the 5-position, was detected in this sulphur-free technical lignin, which had been enriched with carbon compared to the milled wood lignin (MWL) sample of the same wood chips. An increase in phenolic and carboxylic groups was also detected, which makes the lignin accessible to chemical modification. The lignin was determined to be thermally stable up to (273–302 °C) based on its T_{dst 95%} value. Due to the thermal stability, low polydispersity, and possibility to tailor its chemical properties by modification of its hydroxyl groups, possible application areas for the lignin could be in polymeric blends, composites or in resins. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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25 pages, 6691 KiB

Open AccessArticle

Lignocellulosic Biomass as Source for Lignin-Based Environmentally Benign Antioxidants

by Abla Alzagameem, Basma El Khaldi-Hansen, Dominik Büchner, Michael Larkins, Birgit Kamm, Steffen Witzleben and Margit Schulze

Molecules 2018, 23(10), 2664; https://doi.org/10.3390/molecules23102664 - 16 Oct 2018

Cited by 98 | Viewed by 7939

Abstract

Antioxidant activity is an essential aspect of oxygen-sensitive merchandise and goods, such as food and corresponding packaging, cosmetics, and biomedicine. Technical lignin has not yet been applied as a natural antioxidant, mainly due to the complex heterogeneous structure and polydispersity of lignin. This [...] Read more.

Antioxidant activity is an essential aspect of oxygen-sensitive merchandise and goods, such as food and corresponding packaging, cosmetics, and biomedicine. Technical lignin has not yet been applied as a natural antioxidant, mainly due to the complex heterogeneous structure and polydispersity of lignin. This report presents antioxidant capacity studies completed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The influence of purification on lignin structure and activity was investigated. The purification procedure showed that double-fold selective extraction is the most efficient (confirmed by ultraviolet-visible (UV/Vis), Fourier transform infrared (FTIR), heteronuclear single quantum coherence (HSQC) and ³¹P nuclear magnetic resonance spectroscopy, size exclusion chromatography, and X-ray diffraction), resulting in fractions of very narrow polydispersity (3.2–1.6), up to four distinct absorption bands in UV/Vis spectroscopy. Due to differential scanning calorimetry measurements, the glass transition temperature increased from 123 to 185 °C for the purest fraction. Antioxidant capacity is discussed regarding the biomass source, pulping process, and degree of purification. Lignin obtained from industrial black liquor are compared with beech wood samples: antioxidant activity (DPPH inhibition) of kraft lignin fractions were 62–68%, whereas beech and spruce/pine-mixed lignin showed values of 42% and 64%, respectively. Total phenol content (TPC) of the isolated kraft lignin fractions varied between 26 and 35%, whereas beech and spruce/pine lignin were 33% and 34%, respectively. Storage decreased the TPC values but increased the DPPH inhibition. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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17 pages, 2187 KiB

Open AccessFeature PaperArticle

Effects of Process Parameters on Hydrolytic Treatment of Black Liquor for the Production of Low-Molecular-Weight Depolymerized Kraft Lignin

by Zaid Ahmad, Nubla Mahmood, Zhongshun Yuan, Michael Paleologou and Chunbao (Charles) Xu

Molecules 2018, 23(10), 2464; https://doi.org/10.3390/molecules23102464 - 26 Sep 2018

Cited by 15 | Viewed by 4525

Abstract

The present research work aimed at hydrolytic treatment of kraft black liquor (KBL) at 200–300 °C for the production of low-molecular-weight depolymerized kraft lignin (DKL). Various process conditions such as reaction temperature, reaction time, initial kraft lignin (KL) substrate concentration, presence of a [...] Read more.

The present research work aimed at hydrolytic treatment of kraft black liquor (KBL) at 200–300 °C for the production of low-molecular-weight depolymerized kraft lignin (DKL). Various process conditions such as reaction temperature, reaction time, initial kraft lignin (KL) substrate concentration, presence of a catalyst (NaOH), capping agent (phenol) or co-solvent (methanol) were evaluated. The research demonstrated effective depolymerization of KL in KBL at 250–300 °C with NaOH as a catalyst at a NaOH/lignin ratio of about 0.3 (w/w) using diluted KBL (with 9 wt. % KL). Treatment of the diluted KBL at 250 °C for 2 h with 5% addition of methanol co-solvent produced DKL with a weight-average molecular weight (M_w) of 2340 Da, at approx. 45 wt. % yield, and a solid residue at a yield of ≤1 wt. %. A longer reaction time favored the process by reducing the M_w of the DKL products. Adding a capping agent (phenol) helped reduce repolymerization/condensation reactions thereby reducing the M_w of the DKL products, enhancing DKL yield and increasing the hydroxyl group content of the lignin. For the treatment of diluted KBL (with 9 wt. % KL) at 250 °C for 2 h, with 5% addition of methanol co-solvent in the presence of NaOH/lignin ≈ 0.3 (w/w), followed by acidification to recover the DKL, the overall mass balances for C, Na and S were measured to be approx. 74%, 90% and 77%, respectively. These results represent an important step towards developing a cost-effective approach for valorization of KBL for chemicals. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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10 pages, 1927 KiB

Open AccessArticle

Ball Milling’s Effect on Pine Milled Wood Lignin’s Structure and Molar Mass

by Grigory Zinovyev, Ivan Sumerskii, Thomas Rosenau, Mikhail Balakshin and Antje Potthast

Molecules 2018, 23(9), 2223; https://doi.org/10.3390/molecules23092223 - 1 Sep 2018

Cited by 25 | Viewed by 4199

Abstract

The effect of ball milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of crude milled wood lignin (MWLc) preparation is studied to better understand the process’ fundamentals and find optimal conditions for MWL isolation (i.e., [...] Read more.

The effect of ball milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of crude milled wood lignin (MWLc) preparation is studied to better understand the process’ fundamentals and find optimal conditions for MWL isolation (i.e., to obtain the most representative sample with minimal degradation). Softwood (loblolly pine) MWLc preparations with yields of 20–75% have been isolated and characterized based on their molar mass distribution (by Size Exclusion Chromatography (SEC)), hydroxyl groups of different types (³¹P NMR), methoxyl groups (HS-ID GC-MS), and sugar composition (based on methanolysis). Classical MWL purification is not used to access the whole extracted lignin. The results indicate that lignin degradation during ball milling occurs predominantly in the high molar mass fraction and is less pronounced in the low molar mass fraction. This results in a significant decrease in the M_z and M_w of the extracted MWLc with an increase in the yield of MWLc, but has only a very subtle effect on the lignin structure if the yield of MWLc is kept below about 55%. Therefore, no tedious optimization of process variables is necessary to achieve the required MWLc yield in this range for structural studies of softwood MWL. The sugar composition shows higher amounts of pectin components in MWLs of low yields and higher amounts of glucan and mannan in high-yield MWLs, confirming that lignin extraction starts from the middle lamella in the earlier stages of MWL isolation, followed by lignin extraction from the secondary wall region. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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12 pages, 2398 KiB

Open AccessArticle

All-lignocellulosic Fiberboard from Steam Exploded Arundo Donax L.

by Diego Ramos, Nour-Eddine El Mansouri, Francesc Ferrando and Joan Salvadó

Molecules 2018, 23(9), 2088; https://doi.org/10.3390/molecules23092088 - 21 Aug 2018

Cited by 25 | Viewed by 4765

Abstract

This paper explores the possibility of producing all-lignocellulosic fiberboards from Arundo donax L. as a source of lignocellulosic fibers with no synthetic binders. This raw material was steam exploded with a thermomechanical aqueous vapor process in a batch reactor. The Arundo donax raw [...] Read more.

This paper explores the possibility of producing all-lignocellulosic fiberboards from Arundo donax L. as a source of lignocellulosic fibers with no synthetic binders. This raw material was steam exploded with a thermomechanical aqueous vapor process in a batch reactor. The Arundo donax raw material and its obtained pulp were characterized in terms of chemical composition and the results were compared to other lignocellulosic materials. The chemical composition of steam exploded Arundo fibers showed high cellulose and a moderate lignin content suggesting it was a good raw material for fiberboard production. The all-lignocellulosic fiberboards were produced on laboratory scale; using the steam exploded Arundo donax by means of a wet process. The effects of pressing pressure on physical and mechanical properties were evaluated and the conditions that optimize the responses were found. The analyzed properties were density (d); water absorption (WA); thickness swelling (TS); modulus of elasticity (MOE); modulus of rupture (MOR); and internal bond strength (IB). The tested levels of the pressing pressure range from 0.35 to 15 MPa. The optimum IB; MOE; MOR; WA and TS were 1.28 MPa, 7439 MPa, 40.4 MPa, 17.6% and 13.3%, respectively. The obtained fiberboards were of very good quality and more than satisfy the requirements of the relevant standard specifications. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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13 pages, 3461 KiB

Open AccessArticle

Cationic High Molecular Weight Lignin Polymer: A Flocculant for the Removal of Anionic Azo-Dyes from Simulated Wastewater

by Shoujuan Wang, Fangong Kong, Pedram Fatehi and Qingxi Hou

Molecules 2018, 23(8), 2005; https://doi.org/10.3390/molecules23082005 - 11 Aug 2018

Cited by 31 | Viewed by 5488

Abstract

The presence of dyes in wastewater effluents made from the textile industry is a major environmental problem due to their complex structure and poor biodegradability. In this study, a cationic lignin polymer was synthesized via the free radical polymerization of lignin with [2-(methacryloyloxy) [...] Read more.

The presence of dyes in wastewater effluents made from the textile industry is a major environmental problem due to their complex structure and poor biodegradability. In this study, a cationic lignin polymer was synthesized via the free radical polymerization of lignin with [2-(methacryloyloxy) ethyl] trimethyl ammonium chloride (METAC) and used to remove anionic azo-dyes (reactive black 5, RB5, and reactive orange 16, RO16) from simulated wastewater. The effects of pH, salt, and concentration of dyes, as well as the charge density and molecular weight of lignin-METAC polymer on dye removal were examined. Results demonstrated that lignin-METAC was an effective flocculant for the removal of dye via charge neutralization and bridging mechanisms. The dye removal efficiency of lignin-METAC polymer was independent of pH. The dosage of the lignin polymer required for reaching the maximum removal had a linear relationship with the dye concentration. The presence of inorganic salts including NaCl, NaNO₃, and Na₂SO₄ had a marginal effect on the dye removal. Under the optimized conditions, greater than 98% of RB5 and 94% of RO16 were removed at lignin-METAC concentrations of 120 mg/L and 105 mg/L in the dye solutions, respectively. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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9 pages, 3685 KiB

Open AccessCommunication

Optimization of Lignin-Based Biocatalyst Production from Pine Sawdust and Wheat Straw

by Froylán M.E. Escalante, Alejandra Carranza-Hernández, Adelina García-Zamora and Efrén Aguilar-Garnica

Molecules 2018, 23(8), 1877; https://doi.org/10.3390/molecules23081877 - 27 Jul 2018

Cited by 1 | Viewed by 4707

Abstract

Pine sawdust and wheat straw are abundant lignocellulosic wastes that have been recently converted into bioethanol under a biochemical platform scheme whose main waste is lignin. Lignin can be transformed into a wide variety of high added-value products, including its functionalization as a [...] Read more.

Pine sawdust and wheat straw are abundant lignocellulosic wastes that have been recently converted into bioethanol under a biochemical platform scheme whose main waste is lignin. Lignin can be transformed into a wide variety of high added-value products, including its functionalization as a catalyst. A key step in the synthesis of a lignin-based catalyst is the sulfonation reaction, whose operating conditions, namely, H₂SO₄ to lignin ratio (mL/g), temperature and time, have been arbitrarily chosen. In this contribution, an optimization methodology (i.e., Box-Behnken) is applied in order to found the operating conditions during the sulfonation reaction that maximizes the total acid sites density of lignin-based catalysts from pine sawdust and wheat straw. The optimization results show that the time in sulfonation reactions can be significantly reduced, compared to those previously reported, without affecting the performance of both catalysts in esterification reactions. These results could be further considered for energy and costs reduction purposes during the conceptual design engineering of the sulfonation reaction. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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12 pages, 6086 KiB

Open AccessArticle

Formation of Lignin Nanoparticles by Combining Organosolv Pretreatment of Birch Biomass and Homogenization Processes

by Leonidas Matsakas, Anthi Karnaouri, Andrzej Cwirzen, Ulrika Rova and Paul Christakopoulos

Molecules 2018, 23(7), 1822; https://doi.org/10.3390/molecules23071822 - 23 Jul 2018

Cited by 69 | Viewed by 5844

Abstract

Valorization of lignocellulosic biomass into a biorefinery scheme requires the use of all biomass components; in this, the lignin fraction is often underutilized. Conversion of lignin to nanoparticles is an attractive solution. Here, we investigated the effect of different lignin isolation processes and [...] Read more.

Valorization of lignocellulosic biomass into a biorefinery scheme requires the use of all biomass components; in this, the lignin fraction is often underutilized. Conversion of lignin to nanoparticles is an attractive solution. Here, we investigated the effect of different lignin isolation processes and a post-treatment homogenization step on particle formation. Lignin was isolated from birch chips by using two organosolv processes, traditional organosolv (OS) and hybrid organosolv-steam explosion (HOS-SE) at various ethanol contents. For post-treatment, lignin was homogenized at 500 bar using different ethanol:water ratios. Isolation of lignin with OS resulted in unshaped lignin particles, whereas after HOS-SE, lignin micro-particles were formed directly. Addition of an acidic catalyst during HOS-SE had a negative impact on the particle formation, and the optimal ethanol content was 50–60% v/v. Homogenization had a positive effect as it transformed initially unshaped lignin into spherical nanoparticles and reduced the size of the micro-particles isolated by HOS-SE. Ethanol content during homogenization affected the size of the particles, with the optimal results obtained at 75% v/v. We demonstrate that organosolv lignin can be used as an excellent starting material for nanoparticle preparation, with a simple method without the need for extensive chemical modification. It was also demonstrated that tuning of the operational parameters results in nanoparticles of smaller size and with better size homogeneity. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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14 pages, 5203 KiB

Open AccessArticle

Production of Micro- and Nanoscale Lignin from Wheat Straw Using Different Precipitation Setups

by Stefan Beisl, Petra Loidolt, Angela Miltner, Michael Harasek and Anton Friedl

Molecules 2018, 23(3), 633; https://doi.org/10.3390/molecules23030633 - 11 Mar 2018

Cited by 33 | Viewed by 5897

Abstract

Micro- and nanosize lignin has recently gained interest due to its improved properties compared to standard lignin available today. As the second most abundant biopolymer after cellulose, lignin is readily available but used for rather low-value applications. Applications for lignin in micro- to [...] Read more.

Micro- and nanosize lignin has recently gained interest due to its improved properties compared to standard lignin available today. As the second most abundant biopolymer after cellulose, lignin is readily available but used for rather low-value applications. Applications for lignin in micro- to nanoscale however, ranging from improvement of mechanical properties of polymer nanocomposites, have bactericidal and antioxidant properties and impregnations to hollow lignin drug carriers for hydrophobic and hydrophilic substances. This research represents a whole biorefinery process chain and compares different precipitation setups to produce submicron lignin particles from lignin containing an organosolv pretreatment extract from wheat straw. A batch precipitation in a stirred vessel was compared with continuous mixing of extract and antisolvent in a T-fitting and mixing in a T-fitting followed by a static mixer. The precipitation in the combination of T-fitting and static mixer with improved precipitation parameters yields the smallest particle size of around 100 nm. Furthermore, drying of particles did not influence the particle sizes negatively by showing decreased particle diameters after the separation process. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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10 pages, 3548 KiB

Open AccessArticle

Lignin from Hardwood and Softwood Biomass as a Lubricating Additive to Ethylene Glycol

by Liwen Mu, Jian Wu, Leonidas Matsakas, Minjiao Chen, Alireza Vahidi, Mattias Grahn, Ulrika Rova, Paul Christakopoulos, Jiahua Zhu and Yijun Shi

Molecules 2018, 23(3), 537; https://doi.org/10.3390/molecules23030537 - 28 Feb 2018

Cited by 40 | Viewed by 5920

Abstract

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving [...] Read more.

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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21 pages, 4349 KiB

Open AccessFeature PaperArticle

Quantification and Variability Analysis of Lignin Optical Properties for Colour-Dependent Industrial Applications

by Olumoye Ajao, Jawad Jeaidi, Marzouk Benali, Andrea M. Restrepo, Naima El Mehdi and Yacine Boumghar

Molecules 2018, 23(2), 377; https://doi.org/10.3390/molecules23020377 - 10 Feb 2018

Cited by 57 | Viewed by 7258

Abstract

Lignin availability has increased significantly due to the commercialization of several processes for recovery and further development of alternatives for integration into Kraft pulp mills. Also, progress in lignin characterization, understanding of its chemistry as well as processing methods have resulted in the [...] Read more.

Lignin availability has increased significantly due to the commercialization of several processes for recovery and further development of alternatives for integration into Kraft pulp mills. Also, progress in lignin characterization, understanding of its chemistry as well as processing methods have resulted in the identification of novel lignin-based products and potential derivatives, which can serve as building block chemicals. However, all these have not led to the successful commercialization of lignin-based chemicals and materials. This is because most analyses and characterizations focus only on the technical suitability and quantify only the composition, functional groups present, size and morphology. Optical properties, such as the colour, which influences the uptake by users for diverse applications, are neither taken into consideration nor analysed. This paper investigates the quantification of lignin optical properties and how they can be influenced by process operating conditions. Lignin extraction conditions were also successfully correlated to the powder colour. About 120 lignin samples were collected and the variability of their colours quantified with the CIE L*a*b* colour space. In addition, a robust and reproducible colour measurement method was developed. This work lays the foundation for identifying chromophore molecules in lignin, as a step towards correlating the colour to the functional groups and the purity. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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11454 KiB

Open AccessArticle

Sustainable Bio-Based Phenol-Formaldehyde Resoles Using Hydrolytically Depolymerized Kraft Lignin

by Homaira Siddiqui, Nubla Mahmood, Zhongshun Yuan, Ferdinando Crapulli, Luana Dessbesell, Amin Rizkalla, Ajay Ray and Chunbao (Charles) Xu

Molecules 2017, 22(11), 1850; https://doi.org/10.3390/molecules22111850 - 28 Oct 2017

Cited by 36 | Viewed by 7344

Abstract

In this study bio-based bio-phenol-formaldehyde (BPF) resoles were prepared using hydrolytically depolymerized Kraft lignin (DKL) as bio-phenol to partially substitute phenol. The effects of phenol substitution ratio, weight-average molecular weight (M_w) of DKL and formaldehyde-to-phenol (F/P) ratio were also investigated [...] Read more.

In this study bio-based bio-phenol-formaldehyde (BPF) resoles were prepared using hydrolytically depolymerized Kraft lignin (DKL) as bio-phenol to partially substitute phenol. The effects of phenol substitution ratio, weight-average molecular weight (M_w) of DKL and formaldehyde-to-phenol (F/P) ratio were also investigated to find the optimum curing temperature for BPF resoles. The results indicated that DKL with M_w ~ 1200 g/mol provides a curing temperature of less than 180 °C for any substitution level, provided that F/P ratios are controlled. Incorporation of lignin reduced the curing temperature of the resin, however, higher M_w DKL negatively affected the curing process. For any level of lignin M_w, the curing temperature was found to increase with lower F/P ratios at lower phenol substitution levels. At 25% and 50% phenol substitution, increasing the F/P ratio allows for synthesis of resoles with lower curing temperatures. Increasing the phenol substitution from 50% to 75% allows for a broader range of lignin M_w to attain low curing temperatures. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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3263 KiB

Open AccessArticle

Valorization of Lignin by Partial Wet Oxidation Using Sustainable Heteropoly Acid Catalysts

by Abayneh Getachew Demesa, Arto Laari, Mika Sillanpää and Tuomas Koiranen

Molecules 2017, 22(10), 1625; https://doi.org/10.3390/molecules22101625 - 28 Sep 2017

Cited by 29 | Viewed by 6011

Abstract

The production of carboxylic acids by partial wet oxidation of alkali lignin at elevated temperatures and pressures was studied experimentally. Two different heteropoly acids, phosphotungstic acid (H₃PW₁₂O₄₀) and phosphomolybdic acid (H₃PMo₁₂O₄₀), [...] Read more.

The production of carboxylic acids by partial wet oxidation of alkali lignin at elevated temperatures and pressures was studied experimentally. Two different heteropoly acids, phosphotungstic acid (H₃PW₁₂O₄₀) and phosphomolybdic acid (H₃PMo₁₂O₄₀), were used to catalyze the oxidation of lignin under hydrothermal conditions. Factors influencing the total yield of carboxylic acids formed during the partial oxidation of lignin were investigated. Formic, acetic and succinic acids were the major products identified. Of the two catalysts used, phosphomolybdic acid gave the most promising results, with carboxylic acid yields and lignin conversions of up to 45% and 95%, respectively. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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Review

Jump to: Research, Other

24 pages, 3487 KiB

Open AccessReview

Recent Advances in Applications of Acidophilic Fungi to Produce Chemicals

by Rehman Javaid, Aqsa Sabir, Nadeem Sheikh and Muhammad Ferhan

Molecules 2019, 24(4), 786; https://doi.org/10.3390/molecules24040786 - 22 Feb 2019

Cited by 13 | Viewed by 4804

Abstract

Processing of fossil fuels is the major environmental issue today. Biomass utilization for the production of chemicals presents an alternative to simple energy generation by burning. Lignocellulosic biomass (cellulose, hemicellulose and lignin) is abundant and has been used for variety of purposes. Among [...] Read more.

Processing of fossil fuels is the major environmental issue today. Biomass utilization for the production of chemicals presents an alternative to simple energy generation by burning. Lignocellulosic biomass (cellulose, hemicellulose and lignin) is abundant and has been used for variety of purposes. Among them, lignin polymer having phenyl-propanoid subunits linked together either through C-C bonds or ether linkages can produce chemicals. It can be depolymerized by fungi using their enzyme machinery (laccases and peroxidases). Both acetic acid and formic acid production by certain fungi contribute significantly to lignin depolymerization. Fungal natural organic acids production is thought to have many key roles in nature depending upon the type of fungi producing them. Biological conversion of lignocellulosic biomass is beneficial over physiochemical processes. Laccases, copper containing proteins oxidize a broad spectrum of inorganic as well as organic compounds but most specifically phenolic compounds by radical catalyzed mechanism. Similarly, lignin peroxidases (LiP), heme containing proteins perform a vital part in oxidizing a wide variety of aromatic compounds with H₂O₂. Lignin depolymerization yields value-added compounds, the important ones are aromatics and phenols as well as certain polymers like polyurethane and carbon fibers. Thus, this review will provide a concept that biological modifications of lignin using acidophilic fungi can generate certain value added and environmentally friendly chemicals. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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22 pages, 3424 KiB

Open AccessFeature PaperReview

Lignin-Derived Biomaterials for Drug Release and Tissue Engineering

by Markus Witzler, Abla Alzagameem, Michel Bergs, Basma El Khaldi-Hansen, Stephanie E. Klein, Dorothee Hielscher, Birgit Kamm, Judith Kreyenschmidt, Edda Tobiasch and Margit Schulze

Molecules 2018, 23(8), 1885; https://doi.org/10.3390/molecules23081885 - 27 Jul 2018

Cited by 140 | Viewed by 10908

Abstract

Renewable resources are gaining increasing interest as a source for environmentally benign biomaterials, such as drug encapsulation/release compounds, and scaffolds for tissue engineering in regenerative medicine. Being the second largest naturally abundant polymer, the interest in lignin valorization for biomedical utilization is rapidly [...] Read more.

Renewable resources are gaining increasing interest as a source for environmentally benign biomaterials, such as drug encapsulation/release compounds, and scaffolds for tissue engineering in regenerative medicine. Being the second largest naturally abundant polymer, the interest in lignin valorization for biomedical utilization is rapidly growing. Depending on its resource and isolation procedure, lignin shows specific antioxidant and antimicrobial activity. Today, efforts in research and industry are directed toward lignin utilization as a renewable macromolecular building block for the preparation of polymeric drug encapsulation and scaffold materials. Within the last five years, remarkable progress has been made in isolation, functionalization and modification of lignin and lignin-derived compounds. However, the literature so far mainly focuses lignin-derived fuels, lubricants and resins. The purpose of this review is to summarize the current state of the art and to highlight the most important results in the field of lignin-based materials for potential use in biomedicine (reported in 2014–2018). Special focus is placed on lignin-derived nanomaterials for drug encapsulation and release as well as lignin hybrid materials used as scaffolds for guided bone regeneration in stem cell-based therapies. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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25 pages, 5701 KiB

Open AccessReview

Production of Flocculants, Adsorbents, and Dispersants from Lignin

by Jiachuan Chen, Armin Eraghi Kazzaz, Niloofar AlipoorMazandarani, Zahra Hosseinpour Feizi and Pedram Fatehi

Molecules 2018, 23(4), 868; https://doi.org/10.3390/molecules23040868 - 10 Apr 2018

Cited by 75 | Viewed by 10138

Abstract

Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, [...] Read more.

Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, and dispersants have a wide range of applications in industry, but they are mainly oil-based chemicals and expensive. This paper reviews the pathways to produce water soluble lignin-based flocculants, adsorbents, and dispersants. It provides information on the recent progress in the possible use of these lignin-based flocculants, adsorbents, and dispersants. It also critically discusses the advantages and disadvantages of various approaches to produce such products. The challenges present in the production of lignin-based flocculants, adsorbents, and dispersants and possible scenarios to overcome these challenges for commercial use of these products in industry are discussed. Full article

(This article belongs to the Special Issue Lignin for Energy, Chemicals and Materials)

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