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Lignocellulose feedstock (LCF) provides a sustainable source of components to produce bioenergy, biofuel, and novel biomaterials. Besides hard and soft wood, so-called low-input plants such as Miscanthus are interesting crops to be investigated as potential feedstock for the second generation biorefinery. The status quo regarding the availability and composition of different plants, including grasses and fast-growing trees (i.e., Miscanthus, Paulownia), is reviewed here. The second focus of this review is the potential of multivariate data processing to be used for biomass analysis and quality control. Experimental data obtained by spectroscopic methods, such as nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR), can be processed using computational techniques to characterize the 3D structure and energetic properties of the feedstock building blocks, including complex linkages. Here, we provide a brief summary of recently reported experimental data for structural analysis of LCF biomasses, and give our perspectives on the role of chemometrics in understanding and elucidating on LCF composition and lignin 3D structure.
Renewable resources gain increasing interest as 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 resource and isolation procedure, lignin shows specific antioxidant and antimicrobial activity. Today, efforts in research and industry are directed toward lignin utilization as 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, 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 drawn 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.
Antioxidant activity is an essential feature required for oxygen-sensitive merchandise and goods, such as food and corresponding packaging as well as materials used in cosmetics and biomedicine. For example, vanillin, one of the most prominent antioxidants, is fabricated from lignin, the second most abundant natural polymer in the world. Antioxidant potential is primarily related to the termination of oxidation propagation reactions through hydrogen transfer. The application of technical lignin as a natural antioxidant has not yet been implemented in the industrial sector, mainly due to the complex heterogeneous structure and polydispersity of lignin. Thus, current research focuses on various isolation and purification strategies to improve the compatibility of lignin material with substrates and enhancing its stabilizing effect.
The antiradical and antimicrobial activity of lignin and lignin-based films are both of great interest for applications such as food packaging additives. The polyphenolic structure of lignin in addition to the presence of O-containing functional groups is potentially responsible for these activities. This study used DPPH assays to discuss the antiradical activity of HPMC/lignin and HPMC/lignin/chitosan films. The scavenging activity (SA) of both binary (HPMC/lignin) and ternary (HPMC/lignin/chitosan) systems was affected by the percentage of the added lignin: the 5% addition showed the highest activity and the 30% addition had the lowest. Both scavenging activity and antimicrobial activity are dependent on the biomass source showing the following trend: organosolv of softwood > kraft of softwood > organosolv of grass. Testing the antimicrobial activities of lignins and lignin-containing films showed high antimicrobial activities against Gram-positive and Gram-negative bacteria at 35 °C and at low temperatures (0-7 °C). Purification of kraft lignin has a negative effect on the antimicrobial activity while storage has positive effect. The lignin release in the produced films affected the activity positively and the chitosan addition enhances the activity even more for both Gram-positive and Gram-negative bacteria. Testing the films against spoilage bacteria that grow at low temperatures revealed the activity of the 30% addition on HPMC/L1 film against both B. thermosphacta and P. fluorescens while L5 was active only against B. thermosphacta. In HPMC/lignin/chitosan films, the 5% addition exhibited activity against both B. thermosphacta and P. fluorescens.
Miscanthus x giganteus Stem Versus Leaf-Derived Lignins Differing in Monolignol Ratio and Linkage
(2019)
As a renewable, Miscanthus offers numerous advantages such as high photosynthesis activity (as a C4 plant) and an exceptional CO2 fixation rate. These properties make Miscanthus very attractive for industrial exploitation, such as lignin generation. In this paper, we present a systematic study analyzing the correlation of the lignin structure with the Miscanthus genotype and plant portion (stem versus leaf). Specifically, the ratio of the three monolignols and corresponding building blocks as well as the linkages formed between the units have been studied. The lignin amount has been determined for M. x giganteus (Gig17, Gig34, Gig35), M. nagara (NagG10), M. sinensis (Sin2), and M. robustus (Rob4) harvested at different time points (September, December, and April). The influence of the Miscanthus genotype and plant component (leaf vs. stem) has been studied to develop corresponding structure-property relationships (i.e., correlations in molecular weight, polydispersity, and decomposition temperature). Lignin isolation was performed using non-catalyzed organosolv pulping and the structure analysis includes compositional analysis, Fourier transform infradred (FTIR), ultraviolet/visible (UV-Vis), hetero-nuclear single quantum correlation nuclear magnetic resonsnce (HSQC-NMR), thermogravimetric analysis (TGA), and pyrolysis gaschromatography/mass spectrometry (GC/MS). Structural differences were found for stem and leaf-derived lignins. Compared to beech wood lignins, Miscanthus lignins possess lower molecular weight and narrow polydispersities (<1.5 Miscanthus vs. >2.5 beech) corresponding to improved homogeneity. In addition to conventional univariate analysis of FTIR spectra, multivariate chemometrics revealed distinct differences for aromatic in-plane deformations of stem versus leaf-derived lignins. These results emphasize the potential of Miscanthus as a low-input resource and a Miscanthus-derived lignin as promising agricultural feedstock.
Bedingt durch die zunehmende Rohstoffknappheit rückt die Suche nach alternativen, nachhaltigen Rohstoffen immer mehr in den Vordergrund. Im Hinblick auf effiziente chemische Verwertbarkeit bietet Lignin zahlreiche Vorteile für verschiedene Anwendungsbereiche, beispielsweise für biobasierte Polyurethanbeschichtungen, etwa zum Korrosionsschutz. Wesentliche Probleme bei der Verwendung von Lignin ergeben sich durch die Heterogenität dieses Naturstoffes sowie durch dessen geringe Polymerisations-Kompatibilität mit Polyolefinen; beide Faktoren beeinflussen u. a die mechanischen Eigenschaften entsprechender Lignin-basierter Polymere. Zudem hängt die konkrete Struktur und damit auch die physikalisch/chemischen Eigenschaften des Lignins stark von der jeweiligen Rohstoffquelle sowie dem Extraktionsverfahren ab.
Ziel dieser Arbeit war die Strukturaufklärung unmodifizierter und modifizierter Kraft-Lignine (KL) und die Untersuchung der Reaktivität aromatischer wie aliphatischer Hydroxygruppen in Abhängigkeit vom pH-Wert. Hierzu wurden unmodifizierte KL aus Schwarzlauge extrahiert und nachfolgend zunächst einer Soxhlet-Extraktion unterzogen, um in Methyltetrahydrofuran lösliche Lignin-Bestandteile – vornehmlich mit aromatischem Charakter – zu gewinnen und so eine verbesserte Löslichkeit auch im bei der nachfolgenden Polyurethansynthese als Lösemittel verwendeten THF zu gewährleisten. Überdies wurden die extrahierten KL via Demethylierung von Methoxygruppen chemisch modifiziert. Zudem wurde mittels nasschemischer Methoden sowie mit differentieller UV/VIS-Spektroskopie die Anzahl an für die Polymerisation erforderliche Hydroxygruppen quantifiziert. Im Anschluss erfolgte, unter besonderer Berücksichtigung ökologischer und ökonomischer Nachhaltigkeitsaspekte, die Synthese Lignin-basierter und funktionalisierter Polyurethanbeschichtungen. Die Oberflächenfunktionalisierung gestattete die Verbesserung der Oberflächenhomogenität sowie - via blend formation - das Einbetten von TPM-Farbstoffen in die Coatings. Hinsichtlich des Einflusses des bei der Extraktion gewählten pH-Wertes (pH = 2 - 5) auf das Verhalten der so gewonnenen KL wurde eine Veränderung sowohl der Struktur der Lignine als auch deren thermischer Stabilität beobachtet. Zudem wurde nachgewiesen, dass mit steigendem pH-Wert die Funktionalität/Reaktivität der aromatischen wie aliphatischen Hydroxygruppen im Lignin zunimmt. Aus unmodifiziertem KL wurden erfolgreich homogene Lignin-basierte Polyurethan-Coatings (LPU-Coatings) synthetisiert; diese LPU-Coatings zeigten bei Verwendung von bei höheren pH-Werten extrahierten KL homogenere, hydrophobe Oberflächenbeschaffenheit sowie gute thermische Stabilität. Zusätzliche Modifizierung der KL durch Demethylierung führte wegen der gesteigerten Anzahl freier Hydroxygruppen zu moderater Reaktivitätssteigerung und damit zu weiterer Verbesserung der Oberflächeneigenschaften hinsichtlich einer homogenen Oberflächenstruktur und -brillanz. Im Hinblick auf den Aspekt der Nachhaltigkeit wurden durch Syntheseoptimierung - bestehend aus Einstellung der Rohstoff-Korngröße, Ultraschallbehandlung und Verwendung des kommerziellen trifunktionellen Polyetherpolyols Lupranol® 3300 in Kombination mit Desmodur® L75 - die Löslichkeit von Lignin im Polyol sowie die thermische Stabilität der LPU-Coatings erhöht. Im Zuge der Syntheseoptimierungen konnte durch verkürzte Trocknungszeiten Energieeinsparung erzielt werden; zudem ließen sich dabei die eingesetzten Mengen kommerziell erhältlicher Chemikalien verringern; beide Einsparungen führten zu Kostenreduktion. Zugleich ließ sich so nicht nur der KL-Anteil im Polymer-Coating erhöhen: Durch eine optimierte wirtschaftliche Einstufensynthese ließ sich die Umsetzung dieser Vorgehensweise auch im Rahmen industrieller Anwendungen vereinfachen. Das Einbetten ausgewählter TPM-Farbstoffe (Kristallviolett und Brilliantgrün) in die LPU-Coatings durch blend formation führte nachweislich zu antimikrobieller Wirkung der Oberflächenbeschichtung, ohne dass die Oberflächenbeschaffenheit an Homogenität verlor. Die im Rahmen dieser Arbeit synthetisierten LPU-Coatings könnten zukünftig als Korrosionsschutz- und antimikrobielle-Beschichtungen ihre Anwendung finden, z. B. in der Landwirtschaft und im Bausektor.
Die im Rahmen der vorliegenden Arbeit gewonnen Erkenntnisse liefern einen Beitrag zur strukturellen Aufklärung des komplexen Biopolymers Lignin. Darüber hinaus stellen die Untersuchungen und Ergebnisse eine Grundlage für eine nachhaltige Herstellung von Lignin-basierten Polymerbeschichtungen dar, die in Zukunft immer mehr an Bedeutung gewinnen werden.
Due to global ecological and economic challenges that have been correlated to the transition from fossil-based to renewable resources, fundamental studies are being performed worldwide to replace fossil fuel raw materials in plastic production. One aspect of current research is the development of lignin-derived polyols to substitute expensive fossil-based polyol components for polyurethane and polyester production. This article describes the synthesis of bioactive lignin-based polyurethane coatings using unmodified and demethylated Kraft lignins. Demethylation was performed to enhance the reaction selectivity toward polyurethane formation. The antimicrobial activity was tested according to a slightly modified standard test (JIS Z 2801:2010). Besides effects caused by the lignins themselves, triphenylmethane derivatives (brilliant green and crystal violet) were used as additional antimicrobial substances. Results showed increased antimicrobial capacity against Staphylococcus aureus. Furthermore, the coating color could be varied from dark brown to green and blue, respectively.
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.