Multi-site sulfonation of lignin for the synthesis of a high-performance dye dispersant

Sulfonated lignin-based dye dispersants have intensively attracted attention due to their low cost, renewability and abundant sources. However, their utilization is limited by the low content of sulfonic groups and high content of hydroxyl groups in their complex lignin structure, which results in various problems such as high reducing rate of dye, severe staining of the fibers and uneven dyeing. Here, the multi-site sulfonated lignin-based dispersants were prepared with high sulfonic group content (2.20 mmol/g) and low hydroxyl content (2.43 mmol/g). When using it as the dispersant, the dye uptake rate was improved from 69.23 % to 98.55 %, the reducing rate was decreased from 20.82 % to 2.03 %, the K/S value was reduced from 0.69 to 0.02, and the particle sizes in dye system before and after high temperature treatment were stabilized below 0.5 μm. Besides, the dispersion effect was significantly improved because no obvious separation between dye and water was observed even if without the assistance of grinding process. In short, the multi-site sulfonation method proposed in this work could remarkably improve the performances of the lignin-based dye dispersants, which would facilitate the development of the dye dispersion and the high value utilization of lignin.

Facile construction of lignin-based network composite hydrogel for efficient adsorption of methylene blue from wastewater

Adsorption method is an effective approach to treat wastewater containing methylene blue. Herein, a cost-effective and eco-friendly lignin-based network composite hydrogel adsorbent (PAA@SML) was constructed by using polyacrylic acid (PAA) to crosslink with sulfomethylated lignin (SML) via free radical polymerization for adsorption of methylene blue (MB) from wastewater. The constructed PAA@SML-0.2 exhibited remarkable adsorption performance towards removal of MB, with a maximum theoretical adsorption capacity of 777.1 mg·g-1. The improved efficiency can be attributed to the well-established network structure and abundant hydrophilic functional groups present in the adsorbent, promoting the interaction between methylene blue (MB) molecules and the adsorption sites of the adsorbent. The adsorption process of the adsorbent for MB followed the pseudo-second-order kinetic and the Langmuir isotherm models, which illustrated the adsorption process attributed to monolayer chemisorption. Mechanism investigation confirmed that the adsorption of MB by PAA@SML-0.2 primarily relied on hydrogen bonding and electrostatic interactions. Moreover, the recyclability test demonstrated excellent regeneration usability and stability of PAA@SML-0.2, and the adsorption capacity maintained above 74.0 % after five cycles. This constructed lignin-based network composite hydrogel is considered to have great potential in the treatment of organic dye in wastewater.

Renewable galactomannan-based biogums with structure regulation to protect zinc metal anodes via blocking and confinement effect

Galactomannan-based biogums were derived from fenugreek, guar, tara, and carob and consisted of mannose and galactose with different ratios, as well as the implementation of high-value utilization was very significant for sustainable development. In this work, renewable and low-cost galactomannan-based biogums were designed and developed as functional coatings protected on the Zn metal anodes. The molecule structure of galactomannan-based biogums were explored on the effect of anticorrosion ability and uniform deposition behavior through the introduction of fenugreek gum, guar gum, tara gum, and carob gum with different ratios of mannose to galactose as 1.2:1, 2:1, 3:1, and 4:1. The existence of biogum protective layers can reduce the contact area between Zn anodes and aqueous electrolyte to enhance the anticorrosion ability of Zn anodes. Rich oxygen-containing groups in galactomannan-based biogums can coordinate with Zn2+ and Zn atoms to form ion conductivity gel layer and adsorb closely on the surface of Zn metal, which can induce uniform deposition of Zn2+ to avoid dendrite growth. Zn electrodes protected by biogums can cycle impressively for 1980 h with 2 mA cm-2 and 2 mAh cm-2. This work can provide a novel strategy to enhance Zn metal anodes' electrochemical performance, as well as implement the high-value application of biomass-based biogums as functional coatings.

Unraveling the Lignin Structural Variation in Different Bamboo Species

The structure of cellulolytic enzyme lignin (CEL) prepared from three bamboo species (Neosinocalamus affinis, Bambusa lapidea, and Dendrocalamus brandisii) has been characterized by different analytical methods. The chemical composition analysis revealed a higher lignin content, up to 32.6% of B. lapidea as compared to that of N. affinis (20.7%) and D. brandisii (23.8%). The results indicated that bamboo lignin was a p-hydroxyphenyl-guaiacyl-syringyl (H-G-S) lignin associated with p-coumarates and ferulates. Advanced NMR analyses displayed that the isolated CELs were extensively acylated at the γ-carbon of the lignin side chain (with either acetate and/or p-coumarate groups). Moreover, a predominance of S over G lignin moieties was found in CELs of N. affinis and B. lapidea, with the lowest S/G ratio observed in D. brandisii lignin. Catalytic hydrogenolysis of lignin demonstrated that 4-propyl-substituted syringol/guaiacol and propanol guaiacol/syringol derived from β-O-4' moieties, and methyl coumarate/ferulate derived from hydroxycinnamic units were identified as the six major monomeric products. We anticipate that the insights of this work could shed light on the sufficient understanding of lignin, which could open a new avenue to facilitate the efficient utilization of bamboo.

Surface Control Behavior toward Crystal Regulation and Anticorrosion Capacity for Zinc Metal Anodes

The commercial application of high-safety aqueous zinc (Zn) secondary batteries is hindered by the poor cycling life of Zn metal anodes. Here we propose a dendrite growth and hydrogen evolution corrosion reaction mechanism from the binding energy of the deposited crystal plane on the Zn surface and the adsorption energy of H₂O molecules on different crystal planes as well as the binding energy of H₂O molecules with Zn²⁺ ions. The biomass-based alkyl polyglucoside (APG) surfactant is adopted as an electrolyte additive of 0.15% to regulate the preferential growth of a parallel Zn(002) plane and enhance the anticorrosion ability of Zn metal anodes. The robust binding and adsorption energies of APG with Zn²⁺ ions in the aqueous electrolyte and the Zn(002) plane on Zn surface generate a synergistic effect to increase the concentration of Zn²⁺ ions on the APG-adsorbed Zn(002) plane, endowing the continuous growth of the preferential parallel Zn(002) plane and the excellent anticorrosion capacity. Accordingly, the long-term cycle stability of 4000 h can be achieved for Zn anodes with APG additives, which is better than that with pure ZnSO₄ electrolyte. With the addition of APG in the anolyte electrolyte, Zn-I₂ full cells display excellent cycling performance (70 mAh g^-1 after 20000 cycles) as compared with that without APG additives.

Designed synthesis of multifunctional lignin-based adsorbent for efficient heavy metal ions removal and electromagnetic wave absorption

Multifunctional lignin-based adsorbents, which have shown great application prospect, have attracted widespread attention. Herein, a series of multifunctional lignin-based magnetic recyclable adsorbents were prepared from carboxymethylated lignin (CL), which was rich in carboxyl group (-COOH). After optimizing the mass ratio of CL to Fe₃O₄, the prepared CL/Fe₃O₄ (3:1) adsorbent showed efficient adsorption capacities for heavy metal ions. The kinetic and isotherm nonlinear fitting studies revealed that the adsorption process followed the second-order kinetic and Langmuir models, and the maximum adsorption capacities (Q_max) of CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent for Pb²⁺, Cu²⁺ and Ni²⁺ ions reached 189.85, 124.43 and 106.97 mg/g, respectively. Meanwhile, after 6 cycles, the adsorption capacities of CL/Fe₃O₄ (3:1) for Pb²⁺, Cu²⁺ and Ni²⁺ ions could keep at 87.4 %, 83.4 % and 82.3 %, respectively. In addition, CL/Fe₃O₄ (3:1) also exhibited excellent electromagnetic wave absorption (EMWA) performance with a reflection loss (RL) of -28.65 dB at 6.96 GHz under the thickness of 4.5 mm, and its effective absorption bandwidth (EAB) achieved 2.24 GHz (6.08-8.32 GHz). In short, the prepared multifunctional CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent with outstanding adsorption capacity for heavy metal ions and superior EMWA capability opens a new avenue for the diversified utilization of lignin and lignin-based adsorbent.

Valorization of lignin through reductive catalytic fractionation of fermented corn stover residues

The fermented corn stover residues are abundant renewable lignin-rich bioresources that show great potential to produce aromatic phenols. However, selective catalytic hydrogenolysis of this residual material still remains challenge to obtain high yields. Herein, a novel strategy to produce monophenolic compounds from the fermented stover over a commercial Pd/C catalyst was proposed. Taking the reaction temperature as the key variable, the highest monomer yield was 28.5 wt% at 220 °C in compaction with that of the pristine corn stover (22.8 wt%). The enhanced monophenol yield was due to the higher contents of lignin and less recalcitrance in the fermented stover. Moreover, the van Krevelen diagram revealed a slight selective CO bond scission of lignin macromolecular during fermentation as well as the dehydration and deoxygenation in hydrogenolysis reaction. Overall, this work opens a new avenue for the valorization of lignin through reductive catalytic fractionation of agricultural wastes.

Lignin-based composites with enhanced mechanical properties by acetone fractionation and epoxidation modification

Epoxy resin is widely used in various fields of the national economy due to its excellent chemical and mechanical properties. Lignin is mainly derived from lignocelluloses as one of the most abundant renewable bioresources. Due to the diversity of lignin sources and the complexity as well as heterogeneity of its structure, the value of lignin has not been fully realized. Herein, we report the utilization of industrial alkali lignin for the preparation of low-carbon and environmentally friendly bio-based epoxy thermosetting materials. Specifically, epoxidized lignin with substituted petroleum-based chemical bisphenol A diglycidyl ether (BADGE) in various proportions was cross-linked to fabricate thermosetting epoxies. The cured thermosetting resin revealed enhanced tensile strength (4.6 MPa) and elongation (315.5%) in comparison with the common BADGE polymers. Overall, this work provides a practicable approach for lignin valorization toward tailored sustainable bioplastics in the context of a circular bioeconomy.

[The mediating role of worker-occupation fit between occupational stress and anxiety symptoms in medical staff]

Objective: To analyze the mediating effect of work-occupation fit between occupational stress and anxiety symptoms in medical staff. Methods: Convenience sampling method was adopted to select participants of one general hospital and three specialized hospitals as respondents for a questionnaire survey in Henan Province from October 2020 to January 2021. A total of 2050 medical staff were investigated, and 1988 valid questionnaires were collected, and the effective rate of the questionnaire was 97.0% (1988/2050) . The "Depression-Anxiety-Stress Scale" and "Worker-Occupation Fit Inventory" were used to evaluate the occupational stress, anxiety symptoms and worker-occupation fit level of medical staff, and the mediation effect of work-occupation fit on the relationship between occupational stress and anxiety symptoms was analyzed using a mediating effect model. Results: The average age of the 1988 medical staff was (32.7±7.8) years old, the positive detection rates of occupational stress and anxiety symptoms were 42.5% (845/1988) and 56.7% (1127/1988) , respectively. Anxiety symptoms of medical staff were positively correlated with occupational stress, negatively correlated with worker-occupation fit (r=0.831, -0.364, P<0.001) , work-occupation fit was negatively correlated with occupational stress (r=-0.259, P<0.001) . The results of the mediation effect analysis showed that occupational stress had a direct effect on anxiety symptoms (β=0.677, BCa 95%CI: 0.648-0.707) , and worker-occupation fit (β=0.047, BCa 95%CI: 0.039-0.056) , characteristic fit (β=0.089, BCa 95%CI: 0.074-0.104) , need-supply fit (β=0.075, BCa 95%CI: 0.062-0.089) , and ability-demand fit (β=0.035, BCa 95%CI: 0.026-0.044) mediated the association between occupational stress and anxiety symptoms in medical staff, with the mediating effect as a percentage of 6.5%, 12.3%, 10.3%, and 4.8%, respectively. Conclusion: Worker-occupation fit has a mediating effect between occupational stress and anxiety symptoms in medical staff, but mainly direct effect.

[Literature analysis of hot topics on occupational noise-induced hearing loss]

Objective: To analyze the literature of related research reports on occupational hearing loss (ONIHL) , study the characteristics of the subject and determine the research hotspots. Methods: In December 2020, PubMed database was searched by bibliometrics for ONIHL published in PubMed database from January 1971 to December 2020. Bicomb 2.03 software was used to extract the subject. The publication year, publication country, source magazine and subject words were summarized and analyzed. Results: A total of 1 473 papers were included in this study, and the number of papers was 66 from 1971 to 1980, and 628 from 2011 to 2020, an increase of nearly 10 times. The top three countries were the United States, China and Germany, with 31.5% (464/1473) , 11.5% (171/1473) and 6.2% (91/1473) ; The cross-sectional study was the most applied type; The top five words for 2011-2020: Mental Illness, polymorphism, cardiovascular disease, high frequency hearing impairment and standards and regulations. Conclusion: Susceptibility Genes, Psychological Disorders, Cardiovascular Diseases and Risk Assessment are hot areas in ONIHL at present. Researchers should focus on major fields and grasp future trends as a whole.

Iatrogenic chorioamniotic separation and septostomy following fetoscopic laser photocoagulation for twin-twin transfusion syndrome

OBJECTIVE

To compare the perinatal outcomes of pregnancies complicated by chorioamniotic separation (CAS) vs septostomy following fetoscopic laser photocoagulation (FLP) for twin-twin transfusion syndrome (TTTS).

METHODS

This was a retrospective cohort analysis of monochorionic diamniotic twin pregnancies with TTTS that underwent FLP at one of two university-affiliated tertiary medical centers between January 2012 and December 2020. CAS and septostomy were diagnosed either during the procedure or by ultrasonography within 24-48 h after FLP. Data on procedure and postprocedure parameters, pregnancy outcomes and survival were collected from the patients' electronic medical records. Pregnancies were stratified according to the presence of CAS, septostomy or neither. Patients diagnosed with both CAS and septostomy were analyzed separately.

RESULTS

Of the 522 women included in the cohort, 38 (7.3%) were diagnosed with CAS, 68 (13.0%) with septostomy and 23 (4.4%) with both CAS and septostomy. The remaining 393 (75.3%) women comprised the control group. Groups did not differ in demographic characteristics. The septostomy group had a lower rate of selective fetal growth restriction than did the CAS and control groups (24.2% vs 36.8% vs 42.7%, respectively; P = 0.017). Moreover, intertwin size discordance was lower in the septostomy group (15.1% vs 23.4% in the CAS group and 25.5% in the control group; P = 0.001). Median gestational age at FLP was significantly lower in the CAS group (19.3 weeks vs 20.4 weeks in controls and 20.9 weeks in the septostomy group; P = 0.049). The rate of delivery prior to 34 weeks was significantly higher in the CAS group (89.2%), followed by the septostomy group (80.9%), compared with the control group (69.0%) (P = 0.006). A secondary analysis demonstrated that patients with both CAS and septostomy presented the highest rates of delivery prior to 34 weeks (100%) and 32 weeks (68.2%).

CONCLUSIONS

CAS and septostomy following laser surgery for TTTS are independently associated with higher rates of preterm delivery. The presence of these two findings in the same patient enhances the risk of prematurity. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Fabricating lignin-based carbon nanofibers as versatile supercapacitors from food wastes

Recently, the high-value utilization of food wastes has attracted great interest in sustainable development. Focusing on the major application of electrochemical energy storage (ECES), light-weight lignin-based carbon nanofibers (LCNFs) were controllably fabricated as supercapacitors from melon seed shells (MSS) and peanut shells (PS) through electrospinning and carbonizing processes. As a result, the optimal specific capacitance of 533.7 F/g in three-electrode system, energy density of 69.7 Wh/kg and power density of 780 W/Kg in two-electrode system were achieved. Surprisingly, the LCNFs also presented a satisfied electromagnetic absorption property: The minimum reflection loss (RL) value reached -37.2 dB at an absorbing frequency of 7.98 GHz with an effective frequency (RL < 10 dB) of 2.24 GHz (6.88 to 9.12 GHz) at a thickness of 3.0 mm. These features make the multifunctional LCNFs highly attractive for light-weight supercapacitor electrodes and electromagnetic wave absorbers applications.

Severity factor kinetic model as a strategic parameter of hydrothermal processing (steam explosion and liquid hot water) for biomass fractionation under biorefinery concept

Hydrothermal processes are an attractive clean technology and cost-effective engineering platform for biorefineries based in the conversion of biomass to biofuels and high-value bioproducts under the basis of sustainability and circular bioeconomy. The deep and detailed knowledge of the structural changes by the severity of biomasses hydrothermal fractionation is scientifically and technological needed in order to improve processes effectiveness, reactors designs, and industrial application of the multi-scale target compounds obtained by steam explosion and liquid hot water systems. The concept of the severity factor [log₁₀ (R_o)] established>30 years ago, continues to be a useful index that can provide a simple descriptor of the relationship between the operational conditions for biomass fractionation in second generation of biorefineries. This review develops a deep explanation of the hydrothermal severity factor based in lignocellulosic biomass fractionation with emphasis in research advances, pretreatment operations and the applications of severity factor kinetic model.

Perinatal risk factors of neurodevelopmental impairment after fetoscopic laser photocoagulation for twin-twin transfusion syndrome: systematic review and meta-analysis

OBJECTIVE

Monochorionic twins with twin-twin transfusion syndrome (TTTS) treated with fetoscopic laser photocoagulation (FLP) are at increased risk of neurodevelopmental impairment (NDI). This meta-analysis aimed to identify the prevalence of and perinatal risk factors for NDI in TTTS survivors treated with FLP.

METHODS

We performed a search in PubMed, EMBASE, Scopus and Web of Science, from inception to 13 February 2021, for studies evaluating perinatal risk factors for NDI in children diagnosed prenatally with TTTS managed by FLP. Data on severity of TTTS at the time of diagnosis, defined according to the Quintero staging system, FLP-related complications and perinatal outcomes were compared between children with a history of TTTS treated with FLP with and those without NDI, which was defined as performance on a cognitive or developmental assessment tool ≥ 2 SD below the mean or a defined motor or sensory disability. A random-effects model was used to pool the mean differences or odds ratios (OR) with the corresponding 95% CIs. Heterogeneity was assessed using the I² statistic.

RESULTS

Nine studies with a total of 1499 TTTS survivors were included. The overall incidence of NDI was 14.0% (95% CI, 9.0-18.0%). The occurrence of NDI in TTTS survivors was associated with later gestational age (GA) at FLP (mean difference, 0.94 weeks (95% CI, 0.50-1.38 weeks); P < 0.0001, I²  = 0%), earlier GA at delivery (mean difference, -1.44 weeks (95% CI, -2.28 to -0.61 weeks); P = 0.0007, I²  = 49%) and lower birth weight (mean difference, -343.26 g (95% CI, -470.59 to -215.92 g); P < 0.00001, I²  = 27%). Evaluation of different GA cut-offs showed that preterm birth before 32 weeks was associated with higher risk for NDI later in childhood (OR, 2.25 (95% CI, 1.02-4.94); P = 0.04, I²  = 35%). No statistically significant difference was found between cases with and those without NDI with respect to Quintero stage of TTTS, recipient or donor status, development of postlaser twin anemia-polycythemia sequence, recurrence of TTTS and incidence of small- for-gestational age or cotwin fetal demise.

CONCLUSIONS

TTTS survivors with later GA at the time of FLP, earlier GA at delivery and lower birth weight are at higher risk of developing NDI. No significant association was found between Quintero stage of TTTS and risk of NDI. Our findings may be helpful for parental counseling and highlight the need for future studies to understand better the risk factors for NDI in TTTS survivors. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Effective fractionation strategy of sugarcane bagasse lignin to fabricate quality lignin-based carbon nanofibers supercapacitors

Lignin is recommended to a tempting alternative precursor of petroleum for fabricating carbon nanofibers (CNFs) due to its high carbon content, low-cost and renewable resources. However, the property of lignin-based carbon nanofibers (LCNFs) is inferior owing to the heterogeneity and 3D-network structure of lignin, which hinders its application in supercapacitors. The latest developments in fractionation technology have shown great potential for overcoming the aforementioned shortcomings. However, most of fractionation methods mainly rely on expensive chemicals and complex reaction process, such as enzymes, multiple solvents, membranes, and dialysis tubes. Herein, we proposed a controllable and effective strategy to fractionate lignin by only changing the ratio of ethanol/water (V/V) as mixture solvent. This gradient extraction method effectively removed the part of lignin with small molecular and branching structure, thus selectively getting the fractionated lignin with high molecular weight, narrow polydispersity index, and good linear structure. Fortunately, when the ratio of ethanol/water was 6:4, the corresponding LCNFs (LCNFs-L60) was obtained with large specific surface area, independent filamentous morphology networks and excellent electrochemical property. Its specific capacitance was up to 405.8 F/g. This way features controllable and sustainable for preparing high-quality LCNFs supercapacitors.

[The correlation between worker-occupation fit and occupational stress in nurses]

Objective: To explore the relationship between the worker-occupation fit and occupational stress in nurses. Methods: Convenience sampling method was used to collect 1 463 nurses from one general hospital and three specialized hospitals from July to October 2019. Depression-anxiety-stress scale (DASS-21) was used to assess the level of occupational stress. Pearson correlation and multivariate logistic regression model were used to analyze the relationship between the worker-occupation fit and occupational stress. Results: The average age of 1 463 nurses was (31.8±7.2) years, and 92.3% (n=1 350) of nurses were female. 47.2% (n=690) of nurses had occupational stress and the mean score of worker-occupation fit was (34.4±6.1). The worker-occupation fit and occupational stress had a significant negative correlation (r=-0.472, P<0.001). The moderate and high level of the worker-occupation fit, characteristic fit, need supply fit, and demand ability fit had protective effects on occupational stress based on the outcome of multivariate logistic regression model [OR (95%CI) were 0.40 (0.28-0.59), 0.16 (0.10-0.24); 0.32 (0.22-0.47), 0.18 (0.11-0.20); 0.33 (0.21-0.52), 0.18 (0.11-0.30); 0.59 (0.37-0.9), 0.54 (0.38-0.78), respectively]. Conclusion: The worker-occupation fit and different types of fit, including characteristic fit, need supply fit, and demand ability fit, could be associated with the occupational stress.

Valorization of Technical Lignin for the Production of Desirable Resins with High Substitution Rate and Controllable Viscosity

The valorization of lignin to replace phenol is significant in the production of phenolic resins. However, a great challenge is to produce lignin-based resin (LR) with a suitable viscosity and high substitution rate of lignin to phenol. In this study, LRs were produced using hardwood technical lignin derived from the pulping industry. Structural analysis of the LRs indicated that the unsubstituted para and ortho carbon atoms of the aromatic ring influenced the curing temperature and activation energy of the resins. The curing kinetics and thermal decomposition study implied that urea and methylene groups in cured LRs were significant factors that affected the thermal stability negatively. The prepared LRs showed desirable features if used as adhesives to make plywood. This is the first approach in which a substitution rate of up to 65 % is achieved for low-reactive-site hardwood lignin, which provides a solution to the challenge of the simultaneous realization of the high addition of lignin and the adaptive viscosity of resins.

Lignin Source and Structural Characterization

Invited for this month's cover is the group of Run-Cang Sun at Dalian Polytechnic University. The image shows that lignin has the potential to produce energy, chemicals, and materials. The Essay itself is available at 10.1002/cssc.202001324.

Unlocking Structure-Reactivity Relationships for Catalytic Hydrogenolysis of Lignin into Phenolic Monomers

Lignin depolymerization into aromatic monomers with high yields and selectivity is essential for the economic feasibility of biorefinery. However, the relationship between lignin structure and its reactivity for upgradeability is still poorly understood, in large part owing to the difficulty in quantitative characterization of lignin structural properties. To overcome these shortcomings, advanced NMR technologies [2D HSQC (heteronuclear single quantum coherence) and ³¹ P] were used to accurately quantify lignin functionalities. Diverse lignin samples prepared from Eucalyptus grandis with varying β-O-4 linkages were subjected to Pd/C-catalyzed hydrogenolysis for efficient C-O bond cleavage to achieve theoretical monomer yields. Strong correlations were observed between the yield of monomeric aromatic compounds and the structural features of lignin, including the contents of β-O-4 linkages and phenolic hydroxyl groups. Notably, a combined yield of up to 44.1 wt % was obtained from β-aryl ether rich in native lignin, whereas much lower yields were obtained from technical lignins low in β-aryl ether content. This work quantitatively demonstrates that the lignin reactivity for acquiring aromatic monomer yields varies depending on the lignin fractionation processes.

Preface to Special Issue of ChemSusChem on Lignin Valorization: From Theory to Practice

In this Editorial, Guest Editors Run-Cang Sun, Joseph S. M. Samec, and Arthur J. Ragauskas introduce the Special Issue of ChemSusChem on Lignin Valorization: From Theory to Practice. The significance of and enormous challenges for the utilization of lignin are reviewed, and the contents of the Special Issue with highly interesting contributions from scientists around the world are outlined.

Lignin Source and Structural Characterization

Lignin is a primary component of lignocellulosic biomass and an underutilized feedstock in the growing pulping and biofuel industries. Currently, over 50 million tons of industrial lignin are produced annually from pulping and bioethanol processes in the world. Around 95 % of industrial lignin is burned as fuel in heat and power plants due to its complicated, destructive, and condensed structures hindering direct industrial utilization, while the remaining 5 % of lignin is used for potential applications, such as additives, binders, dispersants, and surfactants, through modification. Meanwhile, different biorefinery processes also produce a considerable amount of lignin with various structural features and properties. The development of technologies for its structural characterization is currently desirable for lignin valorization, which will improve the techno-economics of applications of lignins in industries.

Research Progress in Lignin-Based Slow/Controlled Release Fertilizer

As a skeleton component of plants, lignin is an organic macromolecule polymer that can be regenerated and naturally degraded. Annually, plant growth produces about 150 billion tons of lignin. In industrial processes such as paper and biomass-refining industry, large amounts of lignin are formed as by-products. Most of technical lignins are directly combusted to obtain heat, which not only is a waste of organic matter but also leads to environmental pollution and other issues. Interestingly, lignin can be used as slow-release carriers and coating materials for fertilizers due to its excellent slow release properties as well as chelating and other functionalities. Preparation of lignin-based slow/controlled release fertilizers can be achieved by sustainable chemical (ammoxidation, Mannich reaction, and other chemical modifications), coating (without or with chemical modification), and chelation modifications. This Review systematically summarizes the methods, mechanisms, and application of the above methods for preparing lignin-based slow/controlled release fertilizers. Although the evaluation standards and methods of lignin-based slow/controlled release fertilizers are not perfect, it is believed that more and more scholars will pay more attention to them to accelerate the development and application of lignin-based slow/controlled release fertilizers, so as to improve their relevant standards. In short, there is an urgent need to improve the preparation process of lignin-based slow/controlled release fertilizers and application as lignin-based slow/controlled release fertilizers to production practice as soon as possible.

Unmasking the heterogeneity of carbohydrates in heartwood, sapwood, and bark of Eucalyptus

In this study, the cellulose and hemicelluloses in heartwood, sapwood, and bark of E. urophylla × E. grandis were comprehensively investigated. The ultrastructural topochemistry of carbohydrates in cell walls was examined in situ by confocal Raman microscopy. Cellulose and alkali-extractable hemicelluloses samples were isolated from different tissues and comparatively characterized by compositional carbohydrate analyses, determination of molecular weights, FT-IR spectroscopy, and XRD and NMR techniques. It was found that among all of the samples, heartwood cellulose had the highest molecular weight as well as the lowest degree of crystallinity. Meanwhile the hemicelluloses in heartwood had higher xylose content, lower degree of branching, slightly lower molecular weights but narrower polydispersity than those in sapwood. The eucalyptus hemicelluloses mainly consisted of (1→4)-β-_D-xylan backbone with glucuronic acid side chains. Furthermore, the hemicelluloses isolated from sapwood had a higher degree of substitution with terminal galactose than those isolated from heartwood and bark.

Engineering aspects of hydrothermal pretreatment: From batch to continuous operation, scale-up and pilot reactor under biorefinery concept

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.

Effect of various pretreatments on improving cellulose enzymatic digestibility of tobacco stalk and the structural features of co-produced hemicelluloses

Hereon, tobacco stalk was deconstructed by lyophilization, ball-milling, ultrasound-assisted alkali extraction, hydrothermal pretreatment (HTP), and alkali presoaking, respectively, followed by dilute alkali cooking to both improve its enzymatic digestibility and isolate the hemicellulosic streams. It was found that a maximum cellulose saccharification rate of 93.5% was achieved from the integrated substrate by ball-milling and dilute alkali cooking, which was 4.4-fold higher than that from the raw material. Interestingly, in this case, 76.9% of hemicelluloses were simultaneously recovered during the integrated treatment. Structural determination indicated that the hemicelluloses released from tobacco stalk by dilute alkali cooking were mixed polysaccharides, and the (1 → 4)-linked β-D-Xylp backbone branched with L-Araf units at O-2/O-3 and 4-O-Me-α-D-GlcpA units at O-2 of the xylose residues was the main structure. In comparison, ultrasound-assisted alkali extraction, ball-milling, and HTP favored the extraction of hemicelluloses with less branched structure and lower molecular weights in the following alkali cooking.

Comparison of emulsifying capacity of two hemicelluloses from moso bamboo in soy oil-in-water emulsions

Oil-in-water food emulsions consisting of natural emulsifiers has been an active field of green scientific inquiry. Here, we extract two types of new hemicellulose-based emulsifiers (H_H and H_L) from holocellulose and dewaxed materials of bamboo (Phyllostachys pubescens), as well as compare their emulsifying soy oil ability, respectively. The main content of H_H is arabinoxylan, while the primary composition in H_L is glucan. The emulsifying capacity of these two types of hemicellulose-based emulsifiers are evaluated by droplet size distribution, surface charge and optical microscopy. Since H_L possesses higher lignin and protein residual contents, the resultant emulsion exhibits smaller droplets and higher emulsion stability. In comparison, H_H emulsifier has almost no emulsifying capacity due to the lack of non-polar groups. This study provides insight into the choice of hemicelluloses-based emulsifiers for the formation of stable oil-in-water food emulsions.

Oil-in-water food emulsions consisting of natural emulsifiers has been an active field of green scientific inquiry.

Total utilization of lignin and carbohydrates in Eucalyptus grandis: an integrated biorefinery strategy towards phenolics, levulinic acid, and furfural

BACKGROUND

Lignocellulosic biomass, which is composed of cellulose, hemicellulose and lignin, represents the most abundant renewable carbon source with significant potential for the production of sustainable chemicals and fuels. Current biorefineries focus on cellulose and hemicellulose valorization, whereas lignin is treated as a waste product and is burned to supply energy to the biorefineries. The depolymerization of lignin into well-defined mono-aromatic chemicals suitable for downstream processing is recognized increasingly as an important starting point for lignin valorization. In this study, conversion of all three components of Eucalyptus grandis into the corresponding monomeric chemicals was investigated using solid and acidic catalyst in sequence.

RESULTS

Lignin was depolymerized into well-defined monomeric phenols in the first step using a Pd/C catalyst. The maximum phenolic monomers yield of 49.8 wt% was achieved at 240 °C for 4 h under 30 atm H₂. In the monomers, 4-propanol guaiacol (12.9 wt%) and 4-propanol syringol (31.9 wt%) were identified as the two major phenolic products with 90% selectivity. High retention of cellulose and hemicellulose pulp was also obtained, which was treated with FeCl₃ catalyst to attain 5-hydroxymethylfurfural, levulinic acid and furfural simultaneously. The optimal reaction condition for the co-conversion of hemicellulose and cellulose was established as 190 °C and 100 min, from which furfural and levulinic acid were obtained in 55.9% and 73.6% yields, respectively. Ultimately, 54% of Eucalyptus sawdust can be converted into well-defined chemicals under such an integrated biorefinery method.

CONCLUSIONS

A two-step process (reductive catalytic fractionation followed by FeCl₃ catalysis) allows the fractionation of all the three biopolymers (cellulose, hemicellulose, and lignin) in Eucalyptus biomass, which provides a promising strategy to make high-value chemicals from sustainable biomass.

Sequential utilization of bamboo biomass through reductive catalytic fractionation of lignin

Reductive catalytic fractionation (RCF) has emerged as a new biorefinery paradigm for the fractionation and sequential utilization of entire components of biomass. Herein, we investigated the RCF of bamboo, a highly abundant herbaceous feedstock, in the presence of Pd/C catalyst. The lignin fraction in bamboo was preferentially depolymerized into well-defined low-molecular-weight phenols, with leaving carbohydrates pulp as a solid residue. In the soluble fraction, four major phenolic compounds, e.g., methyl coumarate/ferulate derived from hydroxycinnamic units and propanol guaiacol/syringol derived from β-O-4 units, were generated up to 41.7 wt% yield based on original lignin content. In the insoluble fraction, the carbohydrates of bamboo were recovered with high retentions of cellulose (68%) and hemicellulose (49%), which upon treatment with enzyme gave glucose (90%) and xylose (85%). Overall, the three major components of bamboo could efficient to be fractionated and converted into useful platform chemicals on the basis of this study.

Structural Features of Alkaline Dioxane Lignin and Residual Lignin from Eucalyptus grandis × E. urophylla

In the present study, lignin from eucalyptus was extracted with 80% alkaline dioxane (0.05 M NaOH) from ball-milled wood and subsequently fractionated by gradient acid precipitation from the filtrate. Meanwhile, the residual lignin was prepared by a double enzymatic hydrolysis process. The yield of the lignin extracted by alkaline dioxane (L_A-2) was 29.5%. The carbohydrate contents and molecular weights of the gradient acid precipitated lignin fractions gradually decreased from 4.90 to 1.36% and from 7770 to 5510 g/mol, respectively, with the decline of the pH value from 6 to 2. Results from two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (NMR) and ³¹P NMR spectroscopy showed an evident reduction of β- O-4 ' linkages with the pH value decrease, while the contents of aliphatic -OH, phenolic -OH, and carboxylic groups displayed an increasing trend. Moreover, the residual lignin exhibited the highest molecular weight (11690 g/mol), the most abundant β- O-4 ' linkages (71.1%), and the highest S/G ratio (4.68).

New Understandings of the Relationship and Initial Formation Mechanism for Pseudo-lignin, Humins, and Acid-Induced Hydrothermal Carbon

The generation of pseudo-lignin as byproduct during the lignocellulose acidic pretreatment has been proposed for many years. However, the detailed formation mechanism is still unclear. Moreover, there is a lack of understanding in the initial reaction during the formation of humins (byproducts in furfural production) and acid-induced hydrothermal carbon (carbon material). In this work, the initial formation of these three substances were investigated. We first found the common feature of their formation process was that carbohydrate-hydrolyzed compounds could form black polymers by condensing in acidic media, but the difference was dependent on the reaction degree. Furthermore, the results revealed that oxidation was an accelerator for condensations during producing black polymers because oxidized compounds could enhance the acidity of the reaction system. However, condensations of oxidized compounds were more difficult to proceed. Meanwhile, during the initial stage, the dominating pathway was that furfural condensed with itself and isomerized xylose via aldol-condensation.

Composite Film Based on Pulping Industry Waste and Chitosan for Food Packaging

Wood auto-hydrolysates (WAH) are obtained in the pulping process by the hydrothermal extraction, which contains lots of hemicelluloses and slight lignin. WAH and chitosan (CS) were introduced into this study to construct WAH-based films by the casting method. The FT-IR results revealed the crosslinking interaction between WAH and CS due to the Millard reaction. The morphology, transmittance, thermal properties and mechanical properties of composite WAH/CS films were investigated. As the results showed, the tensile strength, light transmittances and thermal stability of the WAH-based composite films increased with the increment of WAH/CS content ratio. In addition, the results of oxygen transfer rate (OTR) and water vapor permeability (WVP) suggested that the OTR and WVP values of the films decreased due to the addition of CS. The maximum value of tensile strengths of the composite films achieved 71.2 MPa and the OTR of the films was low as 0.16 cm³·μm·m⁻²·24 h⁻¹·kPa⁻¹, these properties are better than those of other hemicelluloses composite films. These results suggested that the barrier composite films based on WAH and CS will become attractive in the food packaging application for great mechanical properties, good transmittance and low oxygen transfer rate.

Eco-Friendly Phenol-Urea-Formaldehyde Co-condensed Resin Adhesives Accelerated by Resorcinol for Plywood Manufacturing

Eco-friendly and good-performance resin adhesives are needed for wood manufacturing. In this study, phenol-urea-formaldehyde (PUF) resin adhesives were modified by adding various ratios of resorcinol. The properties of PUF, phenol-resorcinol-urea-formaldehyde (PRUF) resin adhesives, and the performances of the prepared plywood were tested. The curing behaviors and the structural features of the PUF and PRUF resin adhesives were investigated via dynamic scanning calorimetry, thermal gravimetric analysis, ¹³C NMR, and cross polarization magic angle spinning ¹³C NMR. The results indicated that 1.3% resorcinol (based on resin, w/w) could decrease the curing temperature and accelerate the curing process after PUF resin modification. The PRUF resin adhesives demonstrated a lower activation energy during the curing process, with up to 28.8% less energy than that of PUF resin adhesive without any curing agent. The plywood demonstrated low formaldehyde emissions (<0.1 mg L^-1) and acceptably high bonding strengths (>1.00 MPa). This work provided a method for preparing an easy-cured and high-performance phenolic resin for wood manufacturing.

Selective Fragmentation of Biorefinery Corncob Lignin into p-Hydroxycinnamic Esters with a Supported Zinc Molybdate Catalyst

Lignin is the largest renewable resource of bioaromatics, and the catalytic fragmentation of lignin into phenolic monomers is increasingly recognized as an important starting point for lignin valorization. Herein, we report that ZnMoO₄ supported on MCM-41 can catalyze the fragmentation of biorefinery technical lignin, enzymatic mild acidolysis lignin, and native lignin derived from corncob to yield lignin oily products that contain 15-37.8 wt % phenolic monomers, in which the high selectivities towards methyl coumarate (1) and methyl ferulate (2) were obtained (up to 78 %). The effects of some key parameters such as the influence of the solvent, reaction temperature, time, H₂ pressure, and catalyst dosage were examined in view of activity and selectivity. The loss of Zn from the catalyst is discussed as the primary cause of deactivation, and the catalytic activity and selectivity can be well preserved in at least six runs by thermal calcination. The high selectivity to 1 and 2 leads to their easy separation and purification from lignin oily product to provide sustainable monomers for the preparation of functional polyether esters and polyesters.

Eucommia ulmoides Oliver: A Potential Feedstock for Bioactive Products

Eucommia ulmoides Oliver (EUO), a traditional Chinese herb, contains a variety of bioactive chemicals, including lignans, iridoids, phenolics, steroids, terpenoids, flavonoids, etc. These bioactive chemicals possess the effective function in nourishing the liver and kidneys and regulating blood pressure. The composition of bioactive chemicals extracted from EUO vary in the different functional parts (leaves, seeds, bark, and staminate flower) and planting models. The bioactive parts of EUO are widely used as raw materials for medicine and food, powdery extracts, herbal formulations, and tinctures. These capabilities hold potential for future development and commercial exploitation of the bioactive products from EUO.

Selective precipitation and characterization of lignin-carbohydrate complexes (LCCs) from Eucalyptus

Six types of lignin-carbohydrate complex (LCC) fractions were isolated from Eucalyptus. The acidic dioxane treatment applied significantly improved the yield of LCCs. The extraction conditions had a limited impact on the LCC structures and linkages. Characterization of the lignin-carbohydrate complex (LCC) structures and linkages promises to offer insight on plant cell wall chemistry. In this case, Eucalyptus LCCs were extracted by aqueous dioxane, and then precipitated sequentially by 70% ethanol, 100% ethanol, and acidic water (pH = 2). The composition and structure of the six LCC fractions obtained by selective precipitation were investigated by sugar analysis, molecular weight determination, and 2D HSQC NMR. It was found that the acidic (0.05-M HCl) dioxane treatment significantly improved the yield of LCCs (66.4% based on Klason lignin), which was higher than the neutral aqueous dioxane extraction, and the extraction condition showed limited impact on the LCC structures and linkages. In the fractionation process, the low-molecular-weight LCCs containing a high content of carbohydrates (60.3-63.2%) were first precipitated by 70% ethanol from the extractable solution. The phenyl glycoside (PhGlc) bonds (13.0-17.0 per 100Ar) and highly acetylated xylans were observed in the fractions recovered by the precipitation with 100% ethanol. On the other hand, such xylan-rich LCCs exhibited the highest frequency of β-O-4 linkages. The benzyl ether (BE) bonds were only detected in the fractions obtained by acidic water precipitation.

Improvement in Wood Bonding Strength of Poly (Vinyl Acetate-Butyl Acrylate) Emulsion by Controlling the Amount of Redox Initiator

Polyvinyl acetate emulsion adhesive has been widely used due to its good bonding performance and environmentally friendly properties. Indeed, the bonding performance can be further improved by copolymerizing with other monomers. In this study, the effect of the adjunction of redox initiator (hydrogen peroxide–tartaric acid, H₂O₂–TA) on the properties of the poly (vinyl acetate-butyl acrylate) (P (VAc–BA)) emulsion adhesive was investigated. With increasing dosage, the reaction became more complete and the obtained film was more compact, as identified via SEM. The core-shell structure of the emulsion particles was confirmed via TEM. Results indicate that while the initiator content increased from 0.5 to 1.0%, a clearer core-shell structure was obtained and the bonding strength of the plywood improved from 2.34 to 2.97 MPa. With the further incorporation of H₂O₂–TA (i.e., 1.5%), the bonding performance deteriorated. The optimum wood bonding strength (2.97 MPa) of the prepared P (VAc-BA) emulsion adhesive was even better than that (2.55 MPa) of a commercial PVAc emulsion adhesive, suggesting its potential application for the wood industry.

One-step process of hydrothermal and alkaline treatment of wheat straw for improving the enzymatic saccharification

BACKGROUND

To increase the production of bioethanol, a two-step process based on hydrothermal and dilute alkaline treatment was applied to reduce the natural resistance of biomass. However, the process required a large amount of water and a long operation time due to the solid/liquid separation before the alkaline treatment, which led to decrease the pure economic profit for production of bioethanol. Therefore, four one-step processes based on order of hydrothermal and alkaline treatment have been developed to enhance concentration of glucose of wheat straw by enzymatic saccharification. The aim of the present study was to systematically evaluated effect for different one-step processes by analyzing the physicochemical properties (composition, structural change, crystallinity, surface morphology, and BET surface area) and enzymatic saccharification of the treated substrates.

RESULTS

In this study, hemicelluloses and lignins were removed from wheat straw and the morphologic structures were destroyed to various extents during the four one-step processes, which were favorable for cellulase absorption on cellulose. A positive correlation was also observed between the crystallinity and enzymatic saccharification rate of the substrate under the conditions given. The surface area of the substrate was positively related to the concentration of glucose in this study. As compared to the control (3.0 g/L) and treated substrates (11.2-14.6 g/L) obtained by the other three one-step processes, the substrate treated by one-step process based on successively hydrothermal and alkaline treatment had a maximum glucose concentration of 18.6 g/L, which was due to the high cellulose concentration and surface area for the substrate, accompanying with removal of large amounts of lignins and hemicelluloses.

CONCLUSIONS

The present study demonstrated that the order of hydrothermal and alkaline treatment had significant effects on the physicochemical properties and enzymatic saccharification of wheat straw. The one-step process based on successively hydrothermal and alkaline treatment is a simple operating and economical feasible method for the production of glucose, which will be further converted into bioethanol.

Assessment of integrated process based on autohydrolysis and robust delignification process for enzymatic saccharification of bamboo

In this study, bamboo (Phyllostachys pubescens) was successfully deconstructed using an integrated process (autohydrolysis and subsequent delignification). Xylooligosaccharides, high-purity lignin, and digestible substrates for producing glucose can be consecutively collected during the integrated process. The structural change and fate of lignin during autohydrolysis process was deeply investigated. Additionally, the structural characteristics and active functional groups of the lignin fractions obtained by these delignification processes were thoroughly investigated by NMR (2D-HSQC and ³¹P NMR) and GPC techniques. The chemical compositions (S, G, and H) and major linkages (β-O-4, β-β, β-5, etc.) were thoroughly assigned and the frequencies of the major lignin linkages were quantitatively compared. Considering the structural characteristics and molecular weights of the lignin as well as enzymatic saccharification ratio of the substrate, the combination of autohydrolysis and organic base-catalyzed ethanol pretreatment was deemed as a promising biorefinery mode in the future based on bamboo feedstock.

Synthesis and Characteristic of Xylan-grafted-polyacrylamide and Application for Improving Pulp Properties

Recently, more attentions have been focused on the exploration of hemicelluloses in the paper industry. In this work, xylan-grafted-polyacrylamide (xylan-g-PAM) biopolymers were synthesized by the graft copolymerization of xylan with acrylamide, and their interaction with fibers was also investigated to improve waste newspaper pulp properties with or without cationic fiber fines. The influences of synthesis conditions were studied on the grafting ratio and the grafting efficiency of biopolymers. Prepared biopolymers were characterized by FTIR, ¹³C NMR, TGA and rheology. It was found that the grafting of PAM on xylan was conductive to improve xylan properties, such as the solubility in water, rheological features, and thermal stability, and the maximum grafting ratio was achieved to 14.7%. Moreover, xylan-g-PAM could obviously enhance the mechanical properties of waste paper pulps. Xylan-g-PAM also played the dominant role in increasing the strength of paper in the combination with prepared cationic fine fibers. When the amounts of xylan-g-PAM and cationic fiber fines were 1.0 wt % and 0.5 wt %, the mechanical properties such as the tensile index was increased by 49.09%, tear index was increased by 36.54%, and the burst index was increased by 20.67%, when compared with the control handsheets. Therefore, xylan-g-PAM as the new biopolymer could be promising in the application of strength agents for the paper industry as well as cationic fiber fines.