Molecular Weight Lignin Research Articles

Synthesis of lignin-based biosurfactant derived from kraft black liquor and its effect on enzymatic hydrolysis of pretreated biomass

Lignin, the main constituent in black liquor of up to 40%, can be converted into a value-added commodity such as a biosurfactant. In this study, lignin was extracted from the Acacia mangium black liquor kraft by acid precipitation (L1S) and ethanol fractionation (L2S). Subsequently, dried lignin was characterized physically and chemically. Biosurfactant was obtained by reacting lignin with polyvinyl alcohol (PVA). To evaluate the fruitfulness of biosurfactants on enzymatic hydrolysis, some optimizations have been conducted: volume ratio PVA: lignin, concentration PVA: lignin, different lignin source, substrate variation, and the effect of an initiator (potassium peroxodisulfate). Lignin by ethanol fractionation resulted in higher lignin content, methoxyl, molecular weight, and syringil but lower particle size and ash content. However, the thermal stability of these two lignins is similar. The ratio of PVA: lignin gave a positive effect on boosting reducing sugar yield (RSY) while the high concentration of PVA: lignin had the opposite effect. The best volume of PVA: lignin was 250 μL with a concentration of biosurfactant 0.4% to get the highest RSY per biomass about 80%. Meanwhile, biosurfactant-based L2S released more RSY than L1S and lignin sigma Aldrich. Kraft process of sweet sorghum bagasse (SSB) obtained more sugar than other substrates such as an alkaline autoclave SSB, jabon soda pulp, and microwave-assisted sulfuric acid pretreated of oil palm empty fruit bunch (EFB). The initiator addition during synthesizing of biosurfactant was predicted to contribute to achieving higher RSY compared to that of that non-initiator addition. This study demonstrates the ability of lignin-based biosurfactants to improve enzymatic hydrolysis yet the best condition was depending on the ratio, concentration, and volume of PVA: lignin, lignin types, substrates, and initiator.

A mild iodocyclohexane demethylation for highly enhancing antioxidant activity of lignin

Lignin, as a natural antioxidant, shows great potential in food engineering and medicine. However, the inherent macromolecular structure, high polydispersity, and few phenolic hydroxy seriously limit its antioxidant activity. In this work, a mild iodocyclohexane demethylation for highly improving the antioxidant activity of lignin was proposed. The results showed –OCH3 content exhibited an almost linear decrease as a function of treating time, and the demethylation and cleavage of β–aryl ether bonds prompt an obvious increase in phenolic hydroxyl content (4.01 mmol/g) and a significant decline in aliphatic hydroxyl (∼0.03 mmol/g). Meanwhile, attributing to the fragmentation of β–O–4, β–β, and β–5 substructures, the polydispersity of lignin molecular weight decreases from 2.7 to 2.2. As a result, the formed catechol-typed lignin showed an outstanding antioxidant activity, with the radical (DPPH·) scavenging index (inverse of concentration for 50% of maximal effect (EC50) value) over 2 000 mL/mg, much superior to the commercial antioxidants (< 500 mL/mg). Further structure-activity relationship analysis implied that the Ph–OH/–OCH3 ratio might act as a key factor influencing the antioxidant activity of lignin. This mild demethylation demonstrates a facile and effective method for highly enhancing the antioxidant activity of lignin and makes the catechol-typed lignin a green and promising product for practical use in food, medicine, and pharmacy.

Physicochemical Properties, Thermal Stability, and Pyrolysis Behavior of Antioxidative Lignin from Water Chestnut Shell Obtained with Ternary Deep Eutectic Solvents.

The molecular weight of lignin extracted from lignocellulosic biomass is an important factor in determining its valorization in industrial processes. Herein, this work aims to explore the extraction of high molecular weight and bioactive lignin from water chestnut shells under mild conditions. Five kinds of deep eutectic solvents were prepared and applied to isolate lignin from water chestnut shells. The extracted lignin was further characterized with element analysis, gel permeation chromatography, and Ultraviolet-visible and Fourier-transform infrared spectroscopy. The distribution of pyrolysis products was identified and quantified with thermogravimetric analysis-Fourier-transform infrared spectroscopy and pyrolysis-gas chromatograph-mass spectrometry. The results showed that choline chloride/ethylene glycol/p-toluenesulfonic acid (1:1.8:0.2 molar ratio) exhibited the highest fractionation efficiency for lignin (84.17% yield) at 100 °C for 2 h. Simultaneously, the lignin showed high purity (90.4%), high relative molecular weight (37,077 g/mol), and excellent uniformity. Furthermore, the aromatic ring structure of lignin remained intact, consisting mainly of p-hydroxyphenyl, syringl, and guaiacyl subunits. The lignin generated a large number of volatile organic compounds during the depolymerization process, mainly composed of ketones, phenols, syringols, guaiacols, esters, and aromatic compounds. Finally, the antioxidant activity of the lignin sample was evaluated with the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay; the lignin from water chestnut shells showed excellent antioxidant activity. These findings confirm that lignin from water chestnut shells has a broad application prospect in valuable chemicals, biofuels and bio-functional materials.

Characterisation of lignins isolated from Bamboo organosolv and kraft black liquor

Bamboo biomass was pulped using organosolv methods: Acetic acid and formic acid; hydrogen peroxide and formic acid; ethanol and water and kraft process with varying concentrations of the cooking chemicals. The properties of the isolated lignin were influenced by the black liquor pH as well as the pulping method. Highest pH (12,8) was recorded for kraft at 70:30 liquor concentration while lowest pH of 2,5 was recorded for both Aceticformic (70:30) and Ethanol/water (70:30 and 60:40). There were obvious differences in the characteristic colours, shapes and sizes of the lignin samples. Bamboo kraft lignin samples formed large pieces much easier than that of Organosolv. Aceticformic (70:30) had the best filteration properties (FC) while Ethanol/water had the poorest. Generally, kraft recorded the highest lignin yield while all the organosolv processes recorded reduced yield. Highest yield (119,25 g/L) was gotten from kraft (50:50) while Peroxyformic (60:40) had the lowest yield of 8,20 g/L. The results showed that higher liquor pH favours total dissolved solid as well as lignin precipitation. As the pH increases, total dissolved solid, yield, Klason and low molecular weight (LMW) lignin content increases while FC decreases. The Klason and LMW lignin content increased with incresing lignin yield.

The Populus alba cationic cell-wall-bound peroxidase (CWPO-C) regulates plant growth, lignin content and composition in poplar

Cationic cell-wall-bound peroxidase (CWPO-C) from Populus alba is the only Class III peroxidase that has been shown to be able to oxidize high molecular weight lignin polymers from sinapyl alcohol and previously, has been believed to be a lignin polymerization-specific peroxidase. However, using an Arabidopsis heterologous expression system, we showed recently that CWPO-C contributes to differentiation or early growth and is involved in auxin catabolism. In this study, to clarify the function of CWPO-C in poplar, we analyzed CWPO-C gene expression and phenotypic changes with CWPO-C overexpression and suppression. Real-time PCR and monitoring promoter activity of CWPO-C using β-glucuronidase (GUS) assay revealed that CWPO-C was strongly expressed in immature tissues, such as the upper stem, axillary buds, and young leaves, in addition to expression in developing xylem. In transgenic poplars in which the expression of CWPO-C was upregulated or suppressed, changes in stem growth, gravitropism bending time, lignin content and syringyl/guaiacyl (S/G) composition were observed. Overexpressing CWPO-C enhanced stem growth and gravitropic response (shorter bending time). With suppressed CWPO-C expression, the lignin content was reduced approximately 45% and the S/G ratio decreased by half. These results strongly suggest that CWPO-C plays a role in differentiation and early growth, as well as in lignin polymerization.

Enzyme-Catalyzed Polymerization of Kraft Lignin from Eucalyptus globulus: Comparison of Bacterial and Fungal Laccases Efficacy.

Kraft lignin, a side-stream from the pulp and paper industry, can be modified by laccases for the synthesis of high added-value products. This work aims to study different laccase sources, including a bacterial laccase from Streptomyces ipomoeae (SiLA) and a fungal laccase from Myceliophthora thermophila (MtL), for kraft lignin polymerization. To study the influence of some variables in these processes, a central composite design (CCD) with two continuous variables (enzyme concentration and reaction time) and three levels for each variable was used. The prediction of the behavior of the output variables (phenolic content and molecular weight of lignins) were modelled by means of response surface methodology (RSM). Moreover, characterization of lignins was performed by Fourier-transform infrared (FTIR) spectroscopy and different nuclear magnetic resonance (NMR) spectroscopy techniques. In addition, antioxidant activity was also analyzed. Results showed that lignin polymerization (referring to polymerization as lower phenolic content and higher molecular weight) occurred by the action of both laccases. The enzyme concentration was the most influential variable in the lignin polymerization reaction within the range studied for SiLA laccase, while the most influential variable for MtL laccase was the reaction time. FTIR and NMR characterization analysis corroborated lignin polymerization results obtained from the RSM.

Light-colored lignin extraction by ultrafiltration membrane fractionation for lignin nanoparticles preparation as UV-blocking sunscreen

A wide range of applications are available for kraft lignin (KL). However, the dark color and wide size distribution of KL make it challenging to use in cosmetics and nanoparticle preparation. In this study, we fractionated KL from a paper-making enterprise using ultrafiltration membrane fractionation, and obtained four kinds of lignin with different molecular weights, namely ultrafiltration lignin (UL). Following that, lignin nanoparticles (ULNPs) were formed by self-assembly from four types of UL. Analyzing the UL and ULNP properties, the low molecular weight lignin, such as ULA, exhibited good antioxidant properties (89.47 %, 5 mg/mL), high brightness (ISO% = 7.55), high L⁎ value (L⁎ = 72.3) and low polydispersity index (PDI = 1.41). The ULNP showed a narrow size distribution (0.8–1.4 m) and high dispersibility in sunscreen. When ULNP was added to sunscreen with 5 % load, its sun protection factor (SPF) value increased from 14.93 to 63.74. Therefore, this study offered an effective way for the comprehensive utilization of pulping waste KL.

High yield production of 1,4-cyclohexanediol and 1,4-cyclohexanediamine from high molecular-weight lignin oil.

The complete utilization of all lignin depolymerization streams obtained from the reductive catalytic fractionation (RCF) of woody biomass into high-value-added compounds is a timely and challenging objective. Here, we present a catalytic methodology to transform beech lignin-derived dimers and oligomers (DO) into well-defined 1,4-cyclohexanediol and 1,4-cyclohexanediamine. The latter two compounds have vast industrial relevance as monomers for polymer synthesis as well as pharmaceutical building blocks. The proposed two-step catalytic sequence involves the use of the commercially available RANEY® Ni catalyst. Therefore, the first step involves the efficient defunctionalization of lignin-derived 2,6-dimethoxybenzoquinone (DMBQ) into 1,4-cyclohexanediol (14CHDO) in 86.5% molar yield, representing a 10.7 wt% yield calculated on a DO weight basis. The second step concerns the highly selective amination of 1,4-cyclohexanediol with ammonia to give 1,4-cyclohexanediamine (14CHDA) in near quantitative yield. The ability to use RANEY® Ni and ammonia in this process holds great potential for future industrial synthesis of 1,4-cyclohexanediamine from renewable resources.

Revealing the relationship between molecular weight of lignin and its color, UV-protecting property

Lignin has great potential as a natural, green, and sustainable broad-spectrum sunscreen active ingredient. However, the coexistence of dark color and sunscreen properties hinders its application in cosmetics. In this study, we focus on the effects of the molecular weight of lignin on tis UV-protecting property and color in order to prepare lignin-based sunscreen with high performance. A prepared sunscreen containing low molecular weight lignin (F5, <1000 g/mol) exhibits good UV-protecting property (sun protection factor (SPF) = 7.14) and light color advantages (ΔE = 46.2). Moreover, a strong synergistic effect on UV-protecting property exists between low molecular weight lignin and ethylhexyl methoxycinnamate (EHMC), resulting in high SPF of F5@EHMC-based sunscreen (55.56). Additionally, added TiO2 can efficiently mitigate the dark color of lignin-based sunscreens due to prominent covering power of TiO2. Moreover, lignin-based sunscreens have good biocompatibility with HaCaT cells. This work is useful for understanding the mechanism of the UV-protecting property and dark color of lignin, and for designing an efficient and safe lignin-based sunscreen.

Quality and quantity of humic-like and fulvic-like acids entrapped in biochars – The effect of various forestry feedstock and pyrolysis temperature of biochars

The objective of the study was to analyze the effect of the pyrolysis temperature (PT) and feedstock on the quality and quantity of humic-like (HLAs) and fulvic-like (FLAs) acids entrapped in the biochars (BioCs) produced from leaves, litter, and straw of forest habitat at different temperatures. Extraction methods, 3DEEM fluorescence and UV–vis spectroscopies enabled to track the changes of HLAs and FLAs concentration, humification degree, lignin type compounds, biological index, aromaticity/aliphaticity, molecular weight and quality of fluorophores. Additionally, the feedstock and PT effect was discussed for the properties of the BioCs and the water extractable organic matter (WEOM). The results showed that the PT increase caused increase in the pH, ash, surface area and negative charge of the BioCs. Woody feedstock resulted in the BioCs with lower ash content, while the BioCs derived from straw revealed low content of organic matter and carbon but high surface area. The feedstock effect was not clear on structural parameters of HLAs and FLAs, however the BioC derived from litter at 750 °C placed HLAs in group of the strong humification. Woody parts in feedstock and increasing PT was the reason of lower humic-like substances content. It was relatively high after pyrolysis at 430 °C and decreased rapidly at higher PTs. The PT increase affected structure of organic fractions. For HLAs, thermal transformation lead to increase of the humification, molecular weight and content of aromatic structures. Changes for FLAs revealed opposite trend due to a greater susceptibility to the pyrolytic partitioning of molecules. PT elevation resulted also in decreasing contribution of protein- and aminoacid- like compounds and degradation of structures derived from lignin-rich feedstocks. These changes were accompanied by progressive decrease in the biological index of HLAs revealing gradual destruction of freshly produced compounds of microbiological origin. WEOM was enriched in organic compounds typical for HLAs fraction, and PT effect was similar to this predominant fraction.

Changes in Chemical Composition of Betung Bamboo (Dendrocalamus asper) after Alkali Immersion Treatment under Various Immersion Times

This research aimed to analyze the change in chemical composition of the betung bamboo (Dendrocalamus asper) strands after alkali immersion treatment under various immersion times. The bamboo culms were converted into strands with the target length, width, and thickness of 70, 25, and 0.5 mm, respectively. Strands were alkali immersion-treated with 1% NaOH solution for 1, 2, and 3 h. Preparation of powder for chemical component analysis refers to the Technical Association of the Pulp and Paper Industry (TAPPI) standard T 264 cm-07 regarding the preparation of wood test samples for chemical analysis. Structural and non-structural bamboo strand chemical components such as holocellulose, alpha-cellulose, hemicellulose, klason lignin, and extractives were analyzed. The results showed that alkali immersion treatment decreased the hemicellulose content from 21.55% before treatment to 20.30% after 3 h immersion. Thus, it changed the holocellulose and alpha-cellulose composition. Alkali immersion treatment also changed the extractive substances dissolved in cold water, hot water, 1% NaOH, and ethanol-benzene solution. The decrease in hemicellulose, molecular weight lignin, and extractive substances would be beneficial for bamboo-oriented strand board manufacture to improve strand adhesion, dimensional stability, mechanical properties, and durability against biological agents attack. Keywords: alkali immersion times, alkali immersion treatment, bamboo, chemical components, pre-treatment

Ultrasonic assisted enhanced catalytic effect of perovskite to promote depolymerization of lignin

The search for renewable energy sources to replace fossil fuel has made lignin a promising carbon-containing resource. In this paper, LaNiO3 perovskite catalyst supported by mesoporous carrier with specific pore structure was prepared by the pore filling of MCM-41 with citrate complex precursors of nickel and lanthanum. Then the catalysts applied to maize straw lignin depolymerization. The results of low-angle XRD, N2 adsorption-desorption, IR spectroscopy and SEM confirmed that the catalyst has been successfully manufactured. Based on the yield of phenolic monomer, low molecular weight lignin derived bio-oil and high molecular weight lignin derived bio-oil as standard, the catalyst showed best catalytic effect when the reaction temperature was 250 °C, the reaction time was 6 h, the ratio of lignin to catalyst mass was 5: 1 and with ultrasonic assist. The yield of phenolic monomer was 11.46 wt% and that of bio-oil was 68.0 wt%. In general, this method is an excellent embodiment of the principle of Lignin-first as well as an excellent strategy for the production of value-added phenolics and high-quality bio-oils from lignin. It plays an important role in promoting the high value utilization of lignin in the future.

Depolymerization of corn cobs using the CO2/lithium bromide trihydrate system for low molecular weight lignin with high antioxidant activity

Depolymerization of corn cobs using the CO2/lithium bromide trihydrate system for low molecular weight lignin with high antioxidant activity

Fractionation of Lignin Streams Using Tangential Flow Filtration

Lignin fractionation helps its valorization process and yields high-quality and -value products. In this study, cascading tangential flow filtration (TFF) was employed for the fractionation of lignin molecules. The lignin-rich stream was obtained from the pretreatment process of corn stover using alkali (NaOH) and cholinium lysinate ([Ch][Lys]) as the catalyst. The effect of TFF (microfiltration, ultrafiltration, and nanofiltration) on lignin molecular weight, sugar distribution, viscosity, and lignin functional groups was investigated. In general, the study concluded that the average molecular weight (MW) and polydispersity of the permeate stream decreased with the reduction of the membrane pore size. TFF was effective in separating the low-MW lignin (200–350 Da) from the aqueous stream. Approximately 2% of monomeric lignin and 10–20% of low-molecular-weight lignin were recovered from NaOH- and [Ch][Lys]-extracted streams. Techno-economic analysis (TEA) results show that a high percentage of the low-MW lignin extraction can be achieved via a cascade TFF membrane operating at high transmembrane pressures (TMPs) and cross membrane velocities. Additionally, a high initial concentration of lignin in the liquid stream plays a critical role in the lignin product yield and recovery cost.

Efficient separation of bagasse lignin by freeze–thaw-assisted p-toluenesulfonic acid pretreatment

Lignin separation is an important procedure that benefits multiple industries and in particular biomass transformation efforts. In this study, bagasse lignin was separated by freeze–thaw-assisted p-toluenesulfonic acid (p-TsOH) pretreatment. The optimal conditions were freezing temperature −60 °C, freezing time 8.0 h, thawing temperature 15 °C, p-TsOH concentration 60%, pretreatment temperature 70 °C, and time 20 min. Lower acid concentrations and temperatures were used compared with traditional p-TsOH pretreatment. The efficiency and selectivity of lignin separation were improved. It was attributed to freeze-thawing, which provided a more efficient physical channel for the effective penetration of p-TsOH. The separation, extraction and purity of lignin were improved to 89.76%, 78.22% and 77.89%, respectively. High separation, high extraction, high purity and large molecular weight lignin samples were obtained. In addition, the recovery and reuse of p-TsOH was enhanced. This provided a new method for the efficient and clean separation of lignin.

Is the Calibration Transfer of Multivariate Calibration Models between High- and Low-Field NMR Instruments Possible? A Case Study of Lignin Molecular Weight.

Although several successful applications of benchtop nuclear magnetic resonance (NMR) spectroscopy in quantitative mixture analysis exist, the possibility of calibration transfer remains mostly unexplored, especially between high- and low-field NMR. This study investigates for the first time the calibration transfer of partial least squares regressions [weight average molecular weight (Mw) of lignin] between high-field (600 MHz) NMR and benchtop NMR devices (43 and 60 MHz). For the transfer, piecewise direct standardization, calibration transfer based on canonical correlation analysis, and transfer via the extreme learning machine auto-encoder method are employed. Despite the immense resolution difference between high-field and low-field NMR instruments, the results demonstrate that the calibration transfer from high- to low-field is feasible in the case of a physical property, namely, the molecular weight, achieving validation errors close to the original calibration (down to only 1.2 times higher root mean square errors). These results introduce new perspectives for applications of benchtop NMR, in which existing calibrations from expensive high-field instruments can be transferred to cheaper benchtop instruments to economize.

Reduction of lignin heterogeneity for improved catalytic performance of lignin nanosphere supported Pd nanoparticles

Lignin heterogeneity, including molecular weight polydispersity and structural complexity, causes undesirable properties of lignin in its valorization. In this regard, the current work focuses on the effect of lignin heterogeneity on the green synthesis of lignin nanosphere (LNS) supported Pd nanoparticles (Pd@LNS) and their catalytic performance. Three lignin fractions with reduced heterogeneity (F1, F2, and F3) were used for LNS fabrication and the as-prepared LNSs were further applied as carriers for Pd nanoparticles (Pd NPs) synthesized using lignin as an in-situ reducer. It was found that the three LNSs exhibited a gradually decreased particle size from F1 to F3, while all of them revealed improved particle size uniformity compared to that from the initial lignin. Owing to the superior reducing power of F1, the LNS prepared from F1 presented the highest loading amount of Pd NPs among the three LNSs. Moreover, these Pd NPs had the smallest particle size and they were dispersed in a much more uniform way than those on the LNSs from F2 and F3. Therefore, the Pd@LNS prepared from F1 exhibited significantly increased catalytic activity in the Cr(VI) reduction compared with those from F2 and F3, as well as the initial lignin. Consequently, the work implies that lignin heterogeneity has considerable influences on the green formation of Pd NPs on LNS, and the catalytic performance of Pd@LNS can be substantially improved using low molecular weight lignin fraction as the feedstock.

Deep eutectic solvent pretreatment of biomass: Influence of hydrogen bond donor and temperature on lignin extraction with high β-O-4 content

Recovering lignin with high β-O-4 content is of prime interest for further high yield depolymerization in low molecular weight phenolic compounds. Pretreatment of lignocellulosic biomass with deep eutectic solvents (DES) was studied to extract this type of tailored lignin from softwood and brewer’s spent grains. In this work, choline chloride (ChCl) based DES with two different hydrogen bond donors (HBD) (lactic acid (LA) and Glycerol (Gly)), were investigated at mild temperatures (60 and 80 °C). The influence of DES pretreatment on extracted lignin molecular weight and structural characteristics was analysed. The acidity and density of DES were proved to affect lignin extraction yield and its features. The lignin characteristics (type of interunits, accessibility) were shown to impact their ability to be recovered. Acidic-DES ChCl:LA at 80 °C with woody biomass gave promising results with 78% of lignin extracted exclusively composed of G units with 61% of β-O-4 linkages with narrow molecular weights distribution.

Utilization of lignin upon successive fractionation and esterification in polylactic acid (PLA)/lignin biocomposite

The study presents the preparation of novel biocomposites based on different lignin fractions and polylactic acid (PLA). Based on the improvement of PLA mechanical properties, we proposed a process to assemble a series of lignin samples and PLA matrix using melt blending to investigate the effects on PLA properties from the perspective of the structure and molecular weight for lignin. The lignin was extracted from pine residue using deep eutectic solvent (DES) and was subjected to fractionation with ethanol and acetone as well as esterification modification with succinic anhydride (SAn). The treated lignin samples were used as additives, which not only improved the mechanical properties of PLA on the basis of retaining its thermal stability, but also granted excellent antimicrobial and biocompatibility properties. The results showed that the molecular weight of lignin was negatively correlated with the phenolic hydroxyl content, and the mechanical properties of the composites were also significantly affected by different molecular weights of lignin, indicating that the inhomogeneity of lignin affects its value-added utilization. The enhanced mechanical properties, antibacterial effect, and steady biocompatibility provide potential possibilities for lignin-based composites in biomedical applications.

Alkylation modification for lignin color reduction and molecular weight adjustment

The application of industrial kraft lignin is limited by its low molecular weight, dark color, and low solubility. In this work, an efficient crosslinking reaction with N,N-Dimethylformamide (DMF) and 1,6-dibromohexane was proposed for adjusting the molecular weight and color of lignin. The chemical structure of alkylation lignin was systematically investigated by gel permeation chromatography (GPC), ultraviolet spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and 2D heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR) spectra. After the alkylation modification, the molecular weights of the lignin were increased to 1643%. The resinol (β-β), β-aryl ether (β-O-4), and phenylcoumaran (β-5) linkages were still the main types of the linkages. The formation of β-β linkage would be inhibited at high temperatures. The color reduction of lignin can be attributed to the low content of chromophores and low packing density. This alkylation lignin will be a new and general approach for developing molecular weight-controlled and light-colored lignins, which can find more applications in cosmetics, packing, and other fields.