Lignocellulosic nanofibril aerogel via gas phase coagulation and diisocyanate modification for solvent absorption.

Cellulose-based aerogels are considered to be carriers that can absorb oils and organic solvents owing to the merits of low density and high surface area. However, the natural hydrophility and poor mechanical strength often obstruct their widespread applications. In this work, Miscanthus-based dual cross-linked lignocellulosic nanofibril (LCNF) aerogels were prepared by gas phase coagulation and methylene diphenyl dissocyanate (MDI) modification. Due to physical and chemical cross-linking strategies, the optimally 4 M-LCNF aerogels had high surface area of 157.9 m2/g, water contact angle of 138.1°, and enhanced compression properties. Moreover, the modified aerogels exhibited absorption performance for various organic solvents, and the maximal absorption capacity of chloroform was 42 g/g aerogel. Because LCNF was directly produced from Miscanthus without using bleaching reagents, this research provided a more sustainable methodology to utilize lignocelluloses to design robust aerogels to deal with the leakage of oil and organic solvents in industrial applications.

One-pot fabrication of lignin-based aromatic porous polymers for efficient removal of bisphenol AF from water.

To remove the bisphenol AF (BPAF) from aqueous solution, two different types of lignin-based aromatic porous polymers (LAPP-1 and LAPP-2) were fabricated via one-pot crosslinking of lignin with 1,4-dichloroxylene and 4,4'-bis(chloromethyl)-1,1'-biphenyl, respectively. The successful synthesis of LAPPs was confirmed by FTIR and XPS, SEM, TEM and N2 adsorption-desorption analysis. Then, batch adsorption experiments were conducted to investigate adsorption properties toward BPAF. Based on the results, the adsorption processes were in accordance with the pseudo-second-order kinetic model and the Freundlich isotherm model, and the thermodynamic studies showed that the adsorption was a spontaneous and exothermic process. It is remarkable that LAPPs exhibited good adsorption performance in wide ranges of pH and ionic strength as well as in recycling process. Notably, compared to LAPP-1, LAPP-2 exhibited higher adsorption capacity for BPAF, which can be ascribed to its higher porosity and content of aromatic ring. Moreover, the comprehensive analysis of experimental and theoretical results indicated that the π-π interactions and pore adsorption may jointly drive the uptake process of BPAF. Considering the simple fabrication method employed and excellent BPAF adsorption performance, LAPPs provided new insights into the development of advanced lignin-based adsorbents for removal of BPAF from water.

Facile synthesis and performance of pH/temperature dual-response hydrogel containing lignin-based carbon dots.

This study demonstrated a facile method to synthesize lignin-based carbon dots (L-CDs) first. Results indicated that the L-CDs had a diameter of 2-5 nm and a graphene-like crystalline structure. It was found that under the optimal synthesis conditions, the fluorescence lifetime of L-CDs was about 12 ns. Within the range of pH 1-10, the fluorescence intensity of the L-CDs and pH value followed a linear relationship. With the contribution of L-CDs, pH/temperature dual responsive hydrogel was synthesized. The elastic modulus G' of hydrogel was much higher than viscous modulus G″. When the PVA content was larger than 10 wt%, the temperature sensitivity and water retention rate gradually decreased. The skeleton of hydrogels had a typical porous honeycomb structure, which made it possible to control its internal pore size by adjusting the content of PVA. There was a linear relationship between the fluorescence intensity of hydrogels and pH value in the range of pH 1-7. Therefore, the pH/temperature dual responsive hydrogel presented a new route for designing tissue engineering scaffolds and drug carriers.

Development of a light activatable lignin nanosphere based spray coating for bioimaging and antimicrobial photodynamic therapy.

Many coating materials are commercially available to combat microbial infections. However, these coatings are difficult to synthesize, and are mostly composed of toxic chemicals. Lignin is an under-explored natural biopolymer with multifaceted potential. Lignin, with adhesive, UV resistant, and antimicrobial properties, is a suitable candidate to develop coating materials. Here we report a smart method to fabricate a sustainable nanospray coating from lignin which does not require any toxic chemicals or additives during synthesis. Initially, we have developed stable lignin nanospheres in a single step in aqueous medium, which were later utilized as a lignin nanospray (LNSR). The LNSR was characterized by dynamic light scattering, scanning electron microscopy, FTIR and other analytical techniques. This LNSR showed remarkable UV blocking, antioxidant and light-activated antimicrobial properties. Interestingly, for the first time, the LNSR demonstrated photoluminescence, making it useful for bioimaging. Moreover, singlet oxygen generation potential was observed in the LNSR, which could render it useful in phototheranostic applications (i.e. light assisted imaging and photodynamic therapy). Further, the LNSR was directly utilized to fabricate a sustainable coating. The nanospray coating exhibited maximum light-induced cell killing when applied to common microbes as detected by live-dead cell imaging. Taken together, the lignin nanospray coating developed via a direct pathway holds great promise to disinfect microbes in the presence of light.

Preparation of sulfur-doped carbon quantum dots from lignin as a sensor to detect Sudan I in an acidic environment.

To achieve a rapid and facile quantitative evaluation of Sudan I illegally added in ketchup, fluorescent carbon quantum dots with excellent stability in acidic environments are required as the actual pH value of ketchup is close to 4.0. In this paper, we developed a green approach to prepare sulfur-doped carbon quantum dots (SCQDs) via hydrothermal treatment of lignin, isolated from pre-hydrolysis liquor, in sulfuric acid solution. The resultant SCQDs from lignin possessed sulfur-containing groups, which exhibited excellent fluorescence with a quantum yield up to 13.5% and good stability in acidic environments with a wide pH range of 0-5.0. Therefore, the SCQDs were successfully employed as a sensor to detect Sudan I in acidic solutions with excellent selectivity and sensitivity. The linear range for Sudan I was 0-40 µM, while the limit of detection was 0.12 µM. In addition, the fluorescent indicator paper functionalized with SCQDs also showed outstanding selectivity to Sudan I. The proposed SCQD sensing system not only displayed application potential for quantitative evaluation of Sudan I dye in practical samples, but also provided a way to convert lignin-based waste into highly valued nanoscale materials.

Study and optimization of parameters affecting the acetylation process of lignin sulfonate biopolymer.

Here, firstly lignin sulfonate was produced from sulfite liquor provided by Mazandaran wood & paper industries (Chookam). Then, the role of effective parameters including reaction temperature, duration time, and amounts of pyridine and acetic anhydride respectively as the catalyst and the esterification agent on the acetylation rate of lignin sulfonate were studied and the process parameters were optimized through multiple experiments. In this investigation, using 1 g lignin sulfonate, the effect of various levels of temperature (ranged from room temperature to 140 °C), reaction time (12-72 h), pyridine volume (0-30 mL), and acetic anhydride volume (5-30 mL) were evaluated. Based on the results of several esterification processes, the optimal values of temperature and reaction time were obtained to be 100 °C and 48 h, respectively, and the optimal volumes of acetic anhydride and pyridine were 20 mL (with equal amounts). Besides, the characterization tests of lignin sulfonate and acetylated lignin sulfonate were performed using FT-IR and NMR techniques. Also in this paper, the morphology and crystallinity/amorphicity of lignin sulfonate and acetylated lignin sulfonate were examined using SEM images and XRD patterns.

Green synthesis of lignin nano- and micro-particles: Physicochemical characterization, bioactive properties and cytotoxicity assessment.

Lignin particles (LPs) have gained prominence due to their biodegradability and bioactive properties. LP production at nano and micro scale produced from organosolv lignin and the understanding of size's effect on their properties is unexplored. This work aimed to produce and characterize lignin nanoparticles and microparticles using a green synthesis process, based on ethanol-solubilized lignin and water. Spherical shape LPs, with a mean size of 75 nm and 215 nm and with a low polydispersity were produced, as confirmed by transmission electron microscopy and dynamic light scattering. LPs thermal stability improved over raw lignin, and the chemical structure of lignin was not affected by the production method. The antimicrobial tests proved that LPs presented a bacteriostatic effect on Escherichiacoli and Salmonella enterica. Regarding the antioxidant potential, LPs had a good antioxidant activity that increased with the reaction time and LPs concentration. LPs also presented an antioxidant effect against intracellular ROS, reducing the intracellular ROS levels significantly. Furthermore, the LPs showed a low cytotoxic effect in Caco-2 cell line. These results showed that LPs at different scales (nano and micro) present biological properties and are safe to be used in different high value industrial sectors, such as biomedical, pharmaceutical and food.

Technological advancement in the synthesis and applications of lignin-based nanoparticles derived from agro-industrial waste residues: A review.

Over the years, lignin has drawn a great deal of interest for their potential use as bio-polymers due to the presence of high amount of phenolic compounds, non-polluting feature and cost-competitiveness as compared to synthetic polymers. However, in order to fast-track their development, different attempts are made towards the usage of lignin in nano form since it exhibits some unique properties in nanoscale range. The present review article provides a detail analysis on the recent advancement in the synthesis and applications of lignin nanoparticles (LNPs) derived from agro-industrial waste residues. In view of that, an in-depth morphological analysis was reviewed to assess the structural influence on the characteristics of LNPs. Further, application of LNPs is explored in different fields including bio-medical engineering, pharmaceuticals, skin-care products and food industries. Finally, the paper is concluded discussing various challenges associated with the synthesis, modification and development with an aspiration of futuristic developments. The readers of this review article will be highly benefitted after acquiring a comprehensive knowledge on LNPs and its different synthesis processes along with various applications.

Phosphorylated kraft lignin with improved thermal stability.

The low cost, environmental friendliness, and reproducibility of kraft lignin (KL) make it a potential candidate for the development of new green material. The phosphorylation of KL can extend its application as a flame-retardant material. Herein, the phosphorylated kraft lignin (PKL) was systematically fabricated in a sustainable process by utilizing a green phosphating reagent, NH4H2PO4, in the presence of urea. The influence of the reaction parameters, i.e., reaction time and temperature, and NH4H2PO4/lignin ratio on the phosphorylation process were investigated. Advanced characterization techniques including 1H NMR, 31P NMR, and XPS confirmed that the phosphorus groups were successfully introduced to lignin molecules. The active phenolic and aliphatic hydroxy groups of kraft lignin underwent a nucleophilic substitution reaction with the phosphate group to generate phosphorylated lignin. Compared with KL, PKL showed excellent thermal stability, and its maximum decomposition temperature was 620 °C compared with 541 °C for KL.

Production of lignin-containing cellulose nanofibers using deep eutectic solvents for UV-absorbing polymer reinforcement.

Lignin-containing cellulose nanofibers (LCNFs) from energy cane bagasse (ECB), were prepared using microwave assisted deep eutectic solvent (MV-DES) treatment in combination with ultrasonication. The yield of lignocellulose is up to 45.2 % with 81.0 % delignification under the optimal reaction condition (110 ℃, 30 min). The resulting LCNF exhibited a highly entangled network, which was caused by the binder role of lignin between cellulose nanofibers. The addition of LCNFs improved the stability of the polyanionic cellulose (PAC) film-forming suspension, which was confirmed by the increased zeta potential and viscosity values. The LCNF / PAC films showed tunable mechanical and UV-resistant properties, depending on the amount and type of LCNFs. PAC films with the addition of 5 % LCNFs (PEF-5 %) showed good mechanical properties (a tensile strength of 55.8 MPa with a 26.3 % strain to break) and high UV protection ability (a UV-transmittance of 2.9 %).

Bio-Based Thermoplastic Starch Composites Reinforced by Dialdehyde Lignocellulose.

In order to improve the mechanical properties and water resistance of thermoplastic starch (TPS), a novel reinforcement of dialdehyde lignocellulose (DLC) was prepared via the oxidation of lignocellulose (LC) using sodium periodate. Then, the DLC-reinforced TPS composites were prepared by an extrusion and injection process using glycerol as a plasticizer. The DLC and LC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the effects of DLC content on the properties of the DLC/TPS composites were investigated via the evaluation of SEM images, mechanical properties, thermal stability, and contact angles. XRD showed that the crystallinity of the DLC decreased due to oxidation damage to the LC. SEM showed good dispersion of the DLC in the continuous TPS phase at low amounts of DLC, which related to good mechanical properties. The tensile strength of the DLC/TPS composite reached a maximum at a DLC content of 3 wt.%, while the elongation at break of the DLC/TPS composites increased with increasing DLC content. The DLC/TPS composites had better thermal stability than the neat TPS. As the DLC content increased, the water resistance first increased, then decreased. The highest tensile strength and elongation at break reached 5.26 MPa and 111.25%, respectively, and the highest contact angle was about 90.7°.

Cytokinin (6-benzylaminopurine) elevates lignification and the expression of genes involved in lignin biosynthesis of carrot.

Carrot is a root crop consumed worldwide and has great nutritional qualities. It is considered as one of the ten most important vegetable crops. Cytokinins are an essential class of the plant hormones that regulate many processes of plant growth. Till now, the effects of cytokinin, BAP, on lignin biosynthesis and related gene expression profiles in carrot taproot is unclear. In order to investigate the effect of applied BAP on lignin-related gene expression profiles, lignin accumulation, anatomical structures, and morphological characters in carrot taproots. Carrot roots were treated with different concentrations of BAP (0, 10, 20, and 30 mg L-1). The results showed that the application of BAP significantly increased plant length, shoot fresh weight, root fresh weight, and taproot diameter. In addition, BAP at 20 mg L-1 or 30 mg L-1 enhanced the average number of petioles. BAP treatment led to increased number and width of xylem vessels. The parenchyma cell numbers of pith were significantly induced in taproots treated with the BAP at a concentration of 30 mg L-1. BAP significantly upregulated most of the expression levels of lignin biosynthesis genes, caused elevated lignin accumulation in carrot taproots. Our results indicate that BAP may play important roles in growth development and lignification in carrot taproots. Our results provide a valuable database for more studies, which may focus on the regulation of root lignification via controlling cytokinin levels in carrot taproots.

Enzymatic-assisted polymerization of the lignin obtained from a macroalgae consortium, using an extracellular laccase-like enzyme (Tg-laccase) from Tetraselmis gracilis.

In the past decade, Mexican coasts have received an enormous influx of macroalgae species, producing serious environmental and public health concerns. Here, we developed a green methodology to generate a new polymer from the lignin contained in the macroalgae. The methodology consists in lignin extraction-by-boiling and its subsequent polymerization with a laccase-like enzyme from the green algae Tetraselmis gracilis (Tg-laccase). Mass spectrometry revealed the presence of guaiacyl (G), p-hydroxyphenyl (H), and sinapyl alcohol as the main monolignols in the lignin from Sargassum sp. On the other hand, MALDI-TOF spectra shows an increase in the size of the lignin chain after enzymatic polymerization process with Tg-laccase. Besides, the characterization of the novel polymer -using 1H NMR, FTIR, SEC-FPLC, and UV/Vis- allowed establishing that during the polymerization process there is a decrease in the number of phenolic groups as well as loss of aromatic protons, which allowed proposing a polimerizacion mechanism. This methodology could be promising in the development of a new lignin-based polymer and would open a new direction for the environmental management of the macroalgae on the Mexican beaches.

Influence of lignin content on the intrinsic modulus of natural fibers and on the stiffness of composite materials.

Agricultural wastes are an alternative to the use of wood in plastic composites, thanks to their abundance, easy availability and other environmental and economic advantages. Agricultural wastes can be processed to obtain lignocellulosic fibers of different compositions that will allow better performance of their composites and the final desired residues' valorization. In this context, the current investigation aims at the management of corn stover wastes to be applied as reinforcement of polypropylene (PP). Four types of lignocellulosic fibers were obtained by submitting the wastes to mechanical, thermomechanical, semi-chemical or chemical processes. Corn fibers were characterized in terms of chemical composition, morphology and mechanical properties. In addition, PP was reinforced with corn fibers and the composites' stiffness evaluated. An assessment of the influence of the fiber composition on the mechanical performance of the composites is conducted. It is observed the key role of lignin content on the intrinsic modulus of the reinforcing fibers, which directly affected the final stiffness of composites. The best performance was achieved for an optimal kappa number between 40 and 50, corresponding to the semi-chemical fibers. The intrinsic modulus of the fibers, as well as the efficiency factor, length and orientation factors in composites were determined via micromechanical models.

Poly(lactic acid)/lignin films with enhanced toughness and anti-oxidation performance for active food packaging.

In this study, grafting of star-like lignin microparticles (LMP) onto PLA (LMP-g-PLA) was successfully realized by ring open polymerization of l-lactide, initiating from the hydroxyl groups on LMP surface. After that, various amount of LMP-g-PLA were melt blended with neat PLA and ethylene-vinyl acetate-glycidyl methacrylate (NPG) to prepare different PLA composites films, by exploiting the interfacial reactions between epoxy groups of NPG and carboxyl and hydroxyl groups of both LMP-g-PLA and PLA. Mechanical test results show that the addition of LMP-g-PLA made a significant contribution to the toughness of PLA/NPG blend, as the elongation at break increased up to 236% in PLA/NPG/1LMP sample. Although the addition of NPG and LMP-g-PLA hindered the crystallization capacity of PLA, good dispersion of LMP-g-PLA and compatibility between LMP and PLA acted as longer tortuous paths, consequently reducing the water vapor transmission rate. Meanwhile, the UV-Vis spectroscopy results showed that PLA/NPG/LMP films have excellent UV resistance behaviour without sacrificing too much the transparency. Results from overall migration tests and testing of anti-oxidant behaviour demonstrated that PLA films blended with NPG and lignin can be used as competitive materials in active food packaging industry.

The Application of Ferric Chloride-Lignin Sulfonate as Shale Inhibitor in Water-Based Drilling Fluid.

A series of ferric chloride-lignin sulfonate (FCLS) was prepared from ferric chloride and lignin sulfonate to be used as shale inhibitor. The swelling rate of clay with FCLS-2 (w/w = 0.3%) decreased to 41.9%. Compared with control, FCLS-2 displayed high inhibitive ability against the hydrating and swelling processes of clay. Thus, the swelling degree of samples with FCLS-2 was much lower than that of the control, as well as the mud ball was more stable in FCLS-2 solution. Essentially, these excellent performances in inhibitor were assigned to the hydrogen bonding, electrostatic interaction and anchoring between FCLS-2 and other components. In addition, FCLS-2 has good compatibility with other common drilling fluid additives, and it can reduce the viscosity of systems, regardless of the room temperature or high temperature.

Structural features of alternative lignin monomers associated with improved digestibility of artificially lignified maize cell walls.

Plant biologists are seeking new approaches for modifying lignin to improve the digestion and utilization of structural polysaccharides in crop cultivars for the production of biofuels, biochemicals, and livestock. To identify promising targets for lignin bioengineering, we artificially lignified maize (Zea mays L.) cell walls with normal monolignols plus 21 structurally diverse alternative monomers to assess their suitability for lignification and for improving fiber digestibility. Lignin formation and structure were assessed by mass balance, Klason lignin, acetyl bromide lignin, gel-state 2D-NMR and thioacidolysis procedures, and digestibility was evaluated with rumen microflora and from glucose production by fungal enzymes following mild acid or base pretreatments. Highly acidic or hydrophilic monomers proved unsuitable for lignin modification because they severely depressed cell wall lignification. By contrast, monomers designed to moderately alter hydrophobicity or introduce cleavable acetal, amide, or ester functionalities into the polymer often readily formed lignin, but most failed to improve digestibility, even after chemical pretreatment. Fortunately, several types of phenylpropanoid derivatives containing multiple ester-linked catechol or pyrogallol units were identified as desirable genetic engineering targets because they readily formed wall-bound polymers and improved digestibility, presumably by blocking cross-linking of lignin to structural polysaccharides and promoting lignin fragmentation during mild acidic and especially alkaline pretreatment.

Boosted selectivity and enhanced capacity of As(V) removal from polluted water by triethylenetetramine activated lignin-based adsorbents.

Low-cost natural polymer lignin has been widely used to remove heavy metal ions from polluted water. But it still has some shortcomings, such as poor removal performance, and weak selective adsorption. Thus, in this study, the lignin prepared by Mannich reaction with black liquor was activated with triethylenetetramine (TETA) to achieve a novel adsorbent with high adsorption rates and a strong selectivity for specific oxygen-containing anions. The adsorption capacity of activated lignin (a-CL) on three oxygen-containing anions (i.e. As(V), P(V) and Cr(VI)) was investigated systematically. The adsorption mechanism of a-CL was elucidated theoretically by the density functional theory (DFT) method. Under the same conditions, the selectivity toward oxygen-containing anions by a-CL followed P(V) < Cr(VI) < As(V). Both FT-IR and DFT simulation results revealed that the hydrogen bond between HAsO42- and N dominated the remarkable selectivity of As (V), yielding a maximum adsorption capacity as high as 62.5 mg g-1. Moreover, the adsorption was very fast with a calculated large adsorption kinetic constant. The removal of As(V) reached 100% within 60 min. The As(V) adsorption kinetics and the adsorption isotherms followed the pseudo-second-order and the Langmuir model. This study provides a way for highly selecting removal of As(VI) from polluted water with the lignin.

Synthesis and characterization of biomass lignin-based PVA super-absorbent hydrogel.

The traditional polyvinyl alcohol composite hydrogel exhibited poor swelling and mechanical properties, which limited its application. To solve these issues, we use biomass lignin as raw material, PVA as matrix template and epichlorohydrin as cross-linker to prepare the Lignin-PVA super-absorbent hydrogels with the swelling ratio of up to 456 g/g under mild condition. When the lignin concentration was increased from vacancy to 5%, the swelling ratio of the Lignin-PVA hydrogels was increased from 92 g/g to 456 g/g. The lignin-based hydrogel synthesized by the higher molecular weight PVA showed better swelling performance. Softwood lignin, hardwood lignin and corncob lignin could also be used to fabricate the Lignin-PVA super-absorbent hydrogels with the swelling ratio of higher than 500 g/g. However, the optimum amount varied from different lignin types, which was related to the molecular weight and phenolic hydroxyl content of lignin. The structural mechanism of the Lignin-PVA hydrogel was proposed to clearly certify the enhancing role of lignin. The adsorption capacity of the Lignin-PVA hydrogel with respect to rhodamine 6G, crystal violet and methylene blue dyes was up to 196, 169 and 179 mg/g, respectively. The Lignin-PVA hydrogel presents great potential applications in the fields of soil water retention and seed cultivation in agriculture, and dye pollutant removal.

One-pot preparation of zwitterion-type lignin polymers.

In this work, a simple approach was examined to prepare zwitterion-type lignin (ZL) in a one-pot reaction system. Kraft lignin (KL) was modified with 3-chloro-2-hydroxypropansulfonic acid sodium salt (CHPSS) and glycidyltrimethylammonium chloride (GTMAC) in an aqueous solution simultaneously. The maximum amounts of sulfonate (1.57 mmol/g) and quaternary-N (2.16 mmol/g) groups on ZL were achieved under the reaction conditions of 7/1 molar ratio of CHPSS/KL, 9/1 molar ratio of GTMAC/KL, 40 g/L concentration of KL, 3/5 molar ratio of NaOH/KL, 4 h reaction time and 80 °C. The chemical structure, thermal stability, and surface activity of the ZL were compared with those of cationic lignin (CL) and sulfonated lignin (SL) produced under optimized conditions. The signals for hydrogen, carbon, and hydrogen­carbon in the spectra of 1H-, 13C-, and HSQC-NMR indicated that the sulfonation and quaternization occurred on both aliphatic and phenolic hydroxy groups of lignin. The flocculation performance of ZL for simulated dye wastewater was further analyzed. The main novelties of this work were the introduction of a one-pot process to simultaneously impart anionic and cationic functional groups onto kraft lignin, and the development of a new biodegradable zwitterion-type flocculant for removing dye pigments from a simulated solution.