Novel Process for Generating Cationic Lignin Based Flocculant

Drying temperature effect on the characteristics of cationically polymerized kraft lignin

In this work, the effect of drying temperature (55-130 °C) on the properties of kraft lignin (KL) polymerized with [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride, as a sustainable polymer (KLM) was investigated. KLM exhibited a 3-fold drop in charge density and a 10 % reduction in water solubility. These alterations were found to be associated with both chemical and physical changes determined by NMR and XPS analyses. At 55 °C, chain interactions were predominant due to electrostatic interactions amongst the pMETAC chains with the electronegative atoms present in KL. At 80, 105, and 130 °C drying temperatures, hydrolysis reactions predominated. The KLM polymer possessed, comparatively, a lesser resistance to thermal degradation than KL, and the KLM polymer had a more uniform thermal degradation behavior across the drying temperatures. Glass transition temperature, Tg, was shown to be comparable for KL across the various drying temperatures. KLM, however, showed an increasing trend as drying temperature increased, up to 130 °C, at which point Tg dropped due to KL degradation. Therefore, the drying temperature has a significant impact on the properties of kraft lignin and its cationic polymerized derivative, and it should be carefully selected to minimize the undesired changes in lignin properties.

Cationic lignin as an efficient and sustainable homogenous catalyst for aqueous Knoevenagel condensation reactions

Knoevenagel condensation is a chemical reaction between aldehydes and active methylene-containing compounds in the presence of heterogeneous, basic homogenous organic or inorganic catalysts and solvent or neat systems. Herein, we introduced a new strategy for this synthesis by using the aqueous solution of cationic kraft lignin (CKL) as a catalyst. The CKL was synthesized through the reaction of kraft lignin (KL) with glycidyltrimethylammonium chloride (GTMAC) in a basic medium. The optimal reaction conditions for the Knoevenagel reaction were 5% catalyst load (weight of catalyst to the weight of benzaldehyde), water as the solvent, and at room temperature, which generated the products with a yield of 97%, illustrating that the CKL was an effective homogenous and green catalyst. The results confirmed that the increase in CKL charge density improved the product yield. The water-insoluble products were easily separated by filtration, and the filtrate containing the catalysts was reused effectively for 5 cycles without a significant decrease in the production yield, which would confirm the advantages of this catalyst for this reaction system. The CKL catalyst exhibited biodegradability comparable to KL. This paper discusses a novel method for Knoevenagel condensation reactions for different aldehydes in a green system utilizing a sustainable, biodegradable catalyst at room temperature and in an aqueous system.

Functionalization of sterculia gum for making platform hydrogels via network formation for use in drug delivery

Recently, various advancements have been made in the development of functional polymeric materials for innovative applications. Herein this work, functionalization of sterculia gum (SG) was carried out via grafting of poly(2-(methacryloyloxy) ethyltrimethylammonium chloride) (METAC)-polyvinyl pyrrolidone (PVP) to develop hydrogel dressings as a platform for use in drug delivery (DD). The innovation of the present work is the exploration of inherent antioxidant and antimicrobial properties of the SG along with antimicrobial characteristic of poly(METAC) and PVP, to design the doxycycline encapsulated hydrogel dressings for better wound healing. FESEM, EDS and AFM analyzed the surface morphology of hydrogels. FTIR, 13C NMR and XRD inferred inclusion of poly(METAC)-PVP into polymers. 13C NMR confirmed the incorporation of poly(METAC) and PVP onto gum by the presence of a peak at 54.74 ppm because of methyl carbon attached to quaternary nitrogen of poly(METAC) and at 45.48 ppm due to the ring carbon of PVP along with FTIR peak at 949 cm-1 because of CN bending of quaternary nitrogen of poy (METAC). Thermal characterization of copolymers has been performed using TGA analysis. One gram of copolymeric hydrogel dressing absorbed 6.51 ± 0.03 g simulated salivary fluid (SSF) and 7.65 ± 0.03 g simulated wound fluid (SWF). Release of doxycycline drug occurred in a sustained manner and followed the Non-Fickian diffusion mechanism from hydrogels. The release profile was most effectively described by Hixon-Crowell kinetic model. Hydrogel demonstrated biocompatibility and expressed thrombogenicity 79.7 ± 4.9 % during its polymer-blood interactions. Copolymer revealed mucoadhesive property, requiring a force of 77.00 ± 0.01 mN to detach from bio-membrane. Additionally, it exhibited antioxidant features, showing 43.81 ± 0.286 % free radical scavenging. Hydrogel dressings were mechanically stable and revealed 0.76 ± 0.09 N mm-2 tensile strength and 9.18 ± 0.01 N burst strength. Polymer films were permeable to oxygen and water vapor and were impermeable to microorganisms. Hydrogel dressings exhibited antimicrobial properties against Pseudomonas aeruginosa and Staphylococcus aureus bacteria. Overall, these properties displayed the suitability of hydrogels for wound dressing (WD) applications which may actively enhance wound healing.

Copolymers functionalized with quaternary ammonium compounds under template chain exhibit simultaneously efficient bactericidal and flocculation properties: Characterization, performance and mechanism

In this work, novel multifunctional cationic template copolymers with flocculation and sterilization capabilities were synthesized using a low-pressure ultraviolet (LP-UV) template polymerization method for the removal of kaolin and Escherichia coli (E. coli) from water. The influence of template agents on the structural performance of the copolymers was evaluated through characterization, which showed that template copolymer TPADM possesses a higher cationic charge density and a more complex rough surface, contributing to better flocculation performance than that of the non-template copolymer CPADM. Under optimal experimental conditions, TPADM-1 exhibited removal rates of 98.45% for kaolin and 99% for E. coli (OD600 =0.04), marginally outperforming the non-template copolymer. Simultaneously, TPADM-1 produced good adaptability to kaolin and E. coli wastewater in terms of wide pH, speculating that charge neutralization, adsorption bridging, patching, and sweeping simultaneously dominate the flocculation mechanism. Interestingly, SEM and 3D-EEM analysis confirm that the sterilization of E. coli occurs through two distinct functions: initially adsorption followed by subsequent cell membrane rupture and leakage of cellular contents, ultimately leading to cell death. This research further confirms the feasibility of the designed novel multifunctional copolymers for achieving simultaneous disinfection and turbidity removal, demonstrating practical applicability in real water treatment processes.

Production and characterization of starch-lignin based materials: A review

In their pristine state, starch and lignin are abundant and inexpensive natural polymers frequently considered green alternatives to oil-based and synthetic polymers. Despite their availability and owing to their physicochemical properties; starch and lignin are not often utilized in their pristine forms for high-performance applications. Generally, chemical and physical modifications transform them into starch- and lignin-based materials with broadened properties and functionality. In the last decade, the combination of starch and lignin for producing reinforced materials has gained significant attention. The reinforcing of starch matrices with lignin has received primary focus because of the enhanced water sensitivity, UV protection, and mechanical and thermal resistance that lignin introduces to starch-based materials. This review paper aims to assess starch-lignin materials' production and characterization technologies, highlighting their physicochemical properties, outcomes, challenges, and opportunities. First, this paper describes the current status, sources, and chemical modifications of lignin and starch. Next, the discussion is oriented toward starch-lignin materials and their production approaches, such as blends, composites, plasticized/crosslinked films, and coupled polymers. Special attention is given to the characterization methods of starch-lignin materials, focusing on their advantages, disadvantages, and expected outcomes. Finally, the challenges, opportunities, and future perspectives in developing starch-lignin materials, such as adhesives, coatings, films, and controlled delivery systems, are discussed.

In Situ Copolymerization Studies of Lignin, Acrylamide, and Diallyldimethylammonium Chloride: Mechanism, Kinetics, and Rheology

In this work, free-radical polymerization of kraft lignin, acrylamide (AM), and diallyldimethylammonium chloride (DADMAC) was studied in detail. In situ nuclear magnetic resonance (NMR), rheological analysis, and particle size techniques were conducted to understand the physicochemical characteristics of this copolymerization system. The copolymerization of lignin-AM and lignin-DADMAC had activation energies of 65.7 and 69.3 kJ/mol, respectively, and followed the first-order kinetic model, which was monitored by in situ H1 NMR results. The highest conversions of AM and DADMAC were 96 and 68%, respectively, in the copolymerization of lignin, AM, and DADMAC at the molar ratio of 5.5:2.4:1, pH 2 and 85 °C. The results illustrated that the participation of AM in the reaction was essential for polymerizing DADMAC to lignin due to less steric hindrance of AM than DADMAC facilitating its bridging performance. The monomer conversion ratio and dynamic rheology of the reaction system indicated that lignin acted as an inhibitor in the copolymerization reaction. The particle size analysis of the reaction mixtures reflected the alteration in the size of particles from coarse particles (>300 μm) to fine particles (<10 and 10-50 μm) and suspension to colloidal systems when the reaction progressed. The oscillation study of the reaction media confirmed the gradual increase in the viscosity of the reaction media, illustrating the crosslinking of lignin, AM, and DADMAC.

Waste lignin-based cationic flocculants treating dyeing wastewater: Fabrication, performance, and mechanism

Lignin is often considered to be a complex polymeric structural material with excellent scalability. Reduced pressure distillation, a novel effective way, was proposed to recover reusable waste lignin from textile degumming black liquor. The structure of the recovered material was determined by Fourier Transform Infrared Spectroscopy (FT-IR), Gel Permeation Chromatography (GPC) and Klason Component Analysis. Recycled lignin (RL) was used as the basis for the synthesis of a cationic recycled lignin-based polymers (CRLM) through graft polymerizing cationic monomer (DMC). The optimum synthesis conditions were obtained by conducting orthogonal experiments using the cationicity as the studied parameter, while selecting pH, DMC/RL, reaction temperature and time as independent variables. Recovery experiments showed that the maximum recovery concentration of RL in the black liquor was 5 g/L, with a purity of approximately 83 %. Orthogonal experiments showed that a low DMC/RL ratio was crucial for the synthesis of flocculants. When the molar ratio of DMC/RL was 3:1, the cationicity of the prepared CRLM was as high as 11.32 %. Zeta potential and decolorization experiments also confirmed the stable decolorization performance of CRLM in three kinds of anionic dye wastewater. The experimental results showed that charge neutralization, chemical bonding forces and auxiliary effects play great role to remove anionic dyes, resulting in 94 %, 89 % and 94.9 % removal against Reactive Red 195 (RR195), Acid Red 18 (AR18) and Direct 168 (DB168) respectively. Therefore, this study demonstrated the potential of using recycled waste lignin as synthesize lignin-based flocculants in the field of printing and dyeing wastewater by treating waste with waste.

Supramolecular Photonic Hydrogel for High-Sensitivity Alkaline Phosphatase Detection via Synergistic Driving Force

Structurally-colored photonic hydrogels which are fabricated by introducing hydrogels into thin films or photonic crystal structures are promising candidates for biosensing. Generally, the design of photonic hydrogel biosensors is based on the sensor-analyte interactions induced charge variation within the hydrogel matrix, or chemically grafting binding sites onto the polymer chains, to achieve significant volume change and color variation of the photonic hydrogel. However, relatively low anti-interference capability or complicated synthesis hinder the facile and low-cost fabrication of high-performance photonic hydrogel biosensors. Here, a facilely prepared supramolecular photonic hydrogel biosensor is developed for high-sensitivity detection of alkaline phosphatase (ALP), which is an extensively considered clinical biomarker for a variety of diseases. Responding to ALP results in the broken supramolecular crosslinking and thus increased lattice distancing of the photonic hydrogel driven by synergistic repulsive force between nanoparticles embedded in photonic crystal structure and osmotic swelling pressure. The biosensor shows sensitivity of 7.3 nm spectral shift per mU mL^-1 ALP, with detection limit of 0.52 mU mL^-1 . High-accuracy colorimetric detection can be realized via a smartphone, promoting point-of-care sensing and timely diagnosis of related pathological conditions.

Enhanced flocculation of aluminum oxide particles by lignin-based flocculants in dual polymer systems

Lignin is an abundant phenolic polymer produced vastly in pulping processes that could be further valorized. In this work, anionic (AKLs) and cationic (CKLs) lignin-based polymers were made by polymerizing kraft lignin (KL) with acrylic acid (AA) or [2-(methacryloyloxy) ethyl] trimethyl-ammonium chloride (METAC), respectively. In the polymerization reactions, various molar ratios of AA or METAC to KL were applied to produce AKLs and CKLs with different characteristics. The produced AKLs and CKLs were used in single and dual systems to flocculate aluminum oxide in suspension. To assess the interaction of these lignin-based polymers with the aluminum oxide particles; the zeta potential, adsorption, and flocculation of the colloidal systems were evaluated comprehensively. The flocculation performance of the lignin-derived polymers was compared with that of the homopolymers of AA and METAC (PAA and PMETAC) and commercially used flocculants. In single polymer systems, among the anionic synthesized polymers and homopolymers, KL-A4 (an AKL) was the best flocculant for the aluminum oxide suspensions owing to its largest molecular weight (330 × 10³ g/mol) and highest charge density (-4.2 mmol/g). Remarkably, when KL-A4 and KL-C4 (the CKL with the highest molecular weight and charge density) were used subsequently in a dual polymer system, a larger adsorbed mass and a more viscous adlayer were formed than those of single polymer systems on the surface of aluminum oxide particles. The synergy between KL-A4 and KL-C4 was even stronger than that between homopolymers, which led to more significant adsorption on the aluminum oxide surface and, consequently, more efficient flocculation, producing larger (22 μm) and stronger flocs, regardless of the agitation intensity used in the systems.

Determining the performance of lignin-based flocculants in improving biosludge dewaterability

In the wastewater treatment plant of pulp and paper mills, biosludge dewatering is needed to reduce the sludge handling and disposal costs. It is usually facilitated by means of the addition of synthetic polymers. There is increasing interest in replacing synthetic polymers with biopolymers derived from low value by-products or industrial residuals to improve the environmental footprint of dewatering. In this study, lignin-based flocculants (LBF) were tested for their ability to improve the biosludge dewaterability based on Capillary Suction Time (CST) and dry cake solids achieved with a Crown Press. The results demonstrate that LBFs alone can significantly enhance dewatering with a decrease in CSTs from 72.7 ± 5.1 s (unconditioned biosludge) to 23.3 ± 0.4 s and an increase in dry cake solids after pressing from 7.1 ± 0.5% to 13.9 ± 1.3% with a relatively high dosage of 7.5% w/w. However, with dual conditioning a LBF and 0.1% w/w anionic polyacrylamide (APAM), the required dosage of LBF was reduced to 3% w/w to achieve a dry cake solids content of 13.8 ± 0.4%, the same as that achieved with Zetag8165, a commercial synthetic polymer. LBF addition lowered the particle surface charge, allowing the particles to agglomerate and enhancing for the biosludge dewaterability. The application of LBFs for sludge dewatering offers novel considerable promise for providing more sustainable approaches by optimizing the use of lignin from different extraction processes, applying various types of lignin modifications in combination with anionic polymers, and exploring different methods of disposal or utilization of the dewatered sludge.

Enzymatic synthesis of kraft lignin-acrylate copolymers using an alkaline tolerant laccase

Abstract

Softwood kraft lignin is a major bioresource relevant to the production of sustainable bio-based products. Continued challenges to lignin valorization, however, include poor solubility in organic solvents and in aqueous solutions at neutral pH. Herein, an alkaline tolerant laccase was used to graft acrylate functionalities onto softwood kraft lignin, which is expected to enhance the reactivity of lignin with isocyanate when producing bio-based polyurethanes. Proton nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and high-performance liquid chromatography were used to confirm successful grafting of the acrylate monomer onto lignin and verify the importance of including tert-butyl hydroperoxide as an initiator in the grafting reaction. Laccase-mediated grafting of softwood kraft lignin under alkaline conditions produced lignin products with approximately 30% higher hydroxyl value and higher reactivity toward isocyanate. The reported enzymatic and aqueous process presents an opportunity for the sustainable valorization of softwood kraft lignin.

Key points

• Softwood kraft lignin displayed high phenolic hydroxyl content, polydispersity index and average molecular weight

• Grafting hydroxyethyl acrylate (HEA) monomer onto kraft lignin by laccase was successful at 60 °C and alkaline conditions

• Lignin-HEA grafted copolymer showed an increase in total OH value and an increase in average molecular weight

Supplementary information

The online version contains supplementary material available at 10.1007/s00253-022-11916-z.

Composite Polyelectrolyte Photothermal Hydrogel with Anti-biofouling and Antibacterial Properties for the Real-World Application of Solar Steam Generation

Solar steam generation provides a promising and low-cost solution for freshwater production in energy scarcity areas. However, in real-world applications, evaporators are easily affected by microorganism contamination in source water, causing surface corrosion, structural damage, or even invalidation. Developing anti-biofouling and antibacterial evaporators is significant for long-term stable freshwater production. Herein, a composite polyelectrolyte photothermal hydrogel consisting of sulfobetaine methacrylate (SBMA), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC), and polypyrrole (PPy) with anti-biofouling and antibacterial properties is developed. Crediting sufficient ammonium groups and zwitterionic segments, the optimized polyelectrolyte hydrogel exhibits an ∼90% antibacterial ratio against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) and effectively controls biological contamination. Under 1.0 kW m^-2 solar irradiation, a rapid water evaporation rate of ∼1.690 kg m^-2 h^-1 and a high solar-to-evaporation efficiency of ∼95.94% are achieved with the photothermal hydrogel. We show that a lab-made setup integrated with the hydrogel can realize ∼0.455 kg m^-2 h^-1 freshwater production from seawater under natural sunlight. Moreover, the hydrogel exhibits excellent durability with a stable evaporation rate of ∼1.617 kg m^-2 h^-1 in real seawater for over 6 weeks, making it fullhearted in the real-world application of solar steam generation.

Cationization of Eucalyptus Kraft LignoBoost Lignin: Preparation, Properties, and Potential Applications

Current changes toward a more biobased economy have recently created tremendous renewed interest in using lignin as a valuable source for chemicals and materials. Here, we present a facile cationization approach aiming to impart kraft lignin water-solubility, with similar good features as lignosulfonates. Eucalyptus globulus kraft lignin obtained from a paper mill black liquor by applying the LignoBoost process was used as the substrate. Its reaction with 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTAC) in an aqueous alkaline medium was studied to assess the impact of different reaction conditions (temperature, time, educt concentration, molar CHPTAC-to-lignin ratio) on the degree of cationization. It has been shown that at pH 13, 10 wt % lignin content, 70 °C, and 3 h reaction time, a CHPTAC-to-lignin minimum molar ratio of 1.3 is required to obtain fully water-soluble products. Elemental analysis (4.2% N), size-exclusion chromatography (M_w 2180 Da), and quantitative ¹³C NMR spectroscopy of the product obtained at this limit reactant concentration suggest introduction of 1.2 quaternary ammonium groups per C9 unit and substitution of 75% of the initially available phenolic OH groups. The possible contribution of benzylic hydroxyls to the introduction of quaternary ammonium moieties through a quinone methide mechanism has been proposed. Since both molecular characteristics and degree of substitution, and hence solubility or count of surface charge, of colloidal particles can be adjusted within a wide range, cationic kraft lignins are promising materials for a wide range of applications, as exemplarily demonstrated for flocculation of anionic dyes.

In situ utilization of biomass pretreatment liquor as a novel flocculant for anion dyes removal: Performance and mechanism

In this work, it was first found biomass pretreatment liquor (PL) produced from rice straw (RS) pretreatment with FeCl₃ and polyethylene glycol 400 co-solvent can be used in situ as a new flocculant to remove anionic dyes from wastewater. The removal performance of nine dyes was investigated using various PL doses at different pH values. The experiment indicated that the PL had different flocculation effects on these dyes (color removal efficiency: 42.58-99.84%). Positive color removal results for the dyes were unachievable with six commercial coagulants. Among the nine dyes treated by PL flocculation, the best removal efficiencies for color, turbidity and suspended matter were obtained for Congo red. In the flocculation process, Fe³⁺ plays a role in charge neutralization, lignin nanoparticles (LNP) relies on hydroxyl groups to react instantaneously with the amino groups on the dye, and are bridged together by π-π interactions to promote the formation of floc clusters until they completely settle. Utilization of PL as a flocculant helps pave the way to simultaneously treat waste biomass, waste treatment liquor and dye wastewater. This research is of great significance for future water environment remediation and material development.

A review on physico-chemical delignification as a pretreatment of lignocellulosic biomass for enhanced bioconversion

Effective pretreatment of lignocellulosic biomass (LCB) is one of the most important steps in biorefinery, ensuring the quality and commercial viability of the overall bioprocess. Lignin recalcitrance in LCB is a major bottleneck in biological conversion as the polymerization of lignin with hemicellulose hinders enzyme accessibility and further bioconversion to fuels and chemicals. Therefore, there is a need to delignify LCB to ease further bioprocessing. The efficiency of delignification, quality and quantity of the desired products, and generation of inhibitors depend upon the type of pretreatment employed. This review summarizes different single and integrated physicochemical pretreatments for delignification. Additionally, conditions required for effective delignification and the advantages and drawbacks of each method were evaluated. Advances in overcoming the recalcitrance of residual lignin to saccharification and the methods to recover lignin after delignification are also discussed. Efficient lignin recovery and valorization strategies provide an avenue for the sustainable lignocellulose biorefinery.

Cationic Lignin Polymers as Flocculant for Municipal Wastewater

The radical polymerization of acid-washed and unwashed softwood kraft lignin with [2-(methacryloyloxy) ethyl] trimethylammonium chloride (METAC) was attempted to investigate the production of lignin-based flocculants for simulated wastewater. The incorporation of METAC onto lignin resulted in a cationic charge density (2.3–3.3 meq/g), increased water solubility (89–96% in neutral pH), and increased molecular weight (70,000–210,000 g/mol) of lignin. The lignin–METAC polymers generated from acid-washed lignin had higher molecular weights than those generated from unwashed lignin. The lignin–METAC polymers showed lower resistance to thermal decomposition than unmodified lignin due to the inclusion of PolyMETAC. The unmodified acid-washed lignin samples did not significantly affect the COD of the wastewater, while the unmodified unwashed lignin samples contributed to the COD, implying that unmodified lignin was not suitable for wastewater treatment. The flocculation of wastewater with lignin–METAC led to the chemical oxygen demand (COD) reduction of 17–23% and total organic carbon (TOC) drop of 51–60%. The lignin–METAC polymer with the highest molecular weight (produced from acid-washed lignin) reached the highest COD removal, while lignin–METAC polymer with the highest charge density (produced from unwashed lignin) reached the highest TOC removal. Focused beam reflectance measurement (FBRM) studies revealed that the lignin–METAC polymer produced from acid-washed lignin with a high molecular weight generated larger and more flocs in wastewater than the lignin–METAC polymer produced from unwashed lignin. The comparison of theoretical and experimental dosages required for neutralizing the charges of wastewater demonstrated that charge neutralization was the main flocculation mechanism, although a bridging mechanism was also involved for component removals from wastewater. The use of 1 mg/L of alum along with 65 mg/L lignin–METAC in a dual coagulation–flocculation system led to higher average phosphorous (42%) and COD (44%) removals than the singular flocculation system only using 65 mg/L of lignin–METAC (with phosphorous removals of 3.4% and COD removals of 18.7%). However, lignin–METAC flocculant slightly increased the ammonia–nitrogen content in both singular flocculation and dual coagulation–flocculation systems due to the residual ammonia content of lignin–METAC. The coagulation–flocculation system determined that the use of lignin–METAC (65 mg/L) could reduce the alum dosage significantly while maintaining a similar organic content reduction of 44% for wastewater.

Dual lignin-derived polymeric systems for hazardous ion removals

The functionalization of lignin derivatives for ion removals is a promising method to expedite their use in treating industrial wastewater. In this work, kraft lignin (KL) was polymerized with [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM) or acrylic acid (AA) in an acidic aqueous suspension system to produce cationic and anionic water-soluble lignin polymers with high molecular weights. Then, the interaction of soluble ions and KL-METAM and KL-AA was investigated using a Quartz crystal microbalance (QCM) and a vertical scan analyzer (VSA). The QCM, X-ray photoelectron spectroscopy (XPS) and contact angle measurement results showed that the adsorption efficiency of KL-AA was better than KL-METAM for ions due to the stronger electrostatic interaction, cationic π-interaction, and chelation between ions and KL-AA. Based on adsorption, sedimentation, and aggregate size analyses, the dual polymer systems of KL-AA/KL-METAM were more effective than KL-METAM/KL-AA in removing ions. Among Zn²⁺, Cu²⁺, and K⁺; Zn²⁺ interacted more effectively with polymers in all scenarios because it has higher reactivity for interacting with other elements. As the efficiency of ion removals was more remarkable than past reported findings, the system of KL-AA/KL-METAM may be a promising alternative for the removal of dissolved ions from solutions.

Cationic Photothermal Hydrogels with Bacteria-Inhibiting Capability for Freshwater Production via Solar-Driven Steam Generation

Solar-driven steam generation has been recognized as a sustainable and low-cost solution to freshwater scarcity using abundant solar energy. To harvest freshwater, various interfacial evaporators with rational designs of photothermal materials and structures have been developed concentrating on increasing the evaporation rate in the past few years. However, pathogenic microorganism accumulation on the evaporators by long-duration contact with natural water resources may lead to the deterioration of water transportation and the reduction of the evaporation rate. Here, we develop cationic photothermal hydrogels (CPHs) based on [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) and photothermal polypyrrole (PPy) with bacteria-inhibiting capability for freshwater production via solar-driven steam generation. A rapid water evaporation rate of 1.592 kg m^-2 h^-1 under simulated solar irradiation is achieved with CPHs floating on the water surface. Furthermore, we find that CPHs possess nearly 100% antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The significant bacteria-inhibiting capability is mainly attributed to the large number of ammonium groups on the CPH network. Moreover, we show that CPHs exhibit good applicability with stable evaporation in natural lake water over 2 weeks, and the number of bacteria in purified lake water is significantly reduced. The device based on CPHs can achieve ∼0.49 kg m^-2 h^-1 freshwater production from lake water under natural sunlight. This study provides an attractive strategy for the evaporator to inhibit biological contamination and a potential way for long-term stable freshwater production from natural water resources in practical application.

Flocculation performance of papermaking sludge-based flocculants in different dye wastewater treatment: Comparison with commercial lignin and coagulants

In this study, papermaking sludge-based flocculant (PSBF) and commercial lignin-based flocculant (LBF) have been synthesized by the same graft copolymerization procedures. The structures of alkaline lignin (AL), commercial lignin and the two flocculants were characterized by the modern analytical methods, also, the molecular weights and charge properties were analyzed. The effects of coagulant/flocculant dosages, pH conditions and coexistent dye auxiliaries on flocculation efficiencies were studied in the treatment of reactive turquoise blue (RTB) and disperse red (DR) dye wastewater. The flocculation experiments indicated that PSBF and LBF performed better in the removals of RTB and DR than commercial PAC and PAM. PSBF and LBF were insensitive to pH variation due to their strong charge neutralizing abilities and bridging effects even with the pH changing. In the existence of dye auxiliaries, PSBF and LBF could also exhibit superior decolorization efficiencies by slightly enlarging their dosages. Furthermore, PSBF and LBF had similar flocculation behaviors under all measured experimental conditions, suggesting that PSBF also had excellent flocculation performances even if it was prepared from papermaking sludge.

Revisiting lignin: a tour through its structural features, characterization methods and applications

A pedagogical overview of the main extraction procedures and structural features, characterization methods and state-of-the-art applications.

In-Situ Rheological Studies of Cationic Lignin Polymerization in an Acidic Aqueous System

The chemistry of lignin polymerization was studied in the past. Insights into the rheological behavior of the lignin polymerization system would provide crucial information required for tailoring lignin polymers with desired properties. The in-situ rheological attributes of lignin polymerization with a cationic monomer, [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METAC), were studied in detail in this work. The influences of process conditions, e.g., temperature, component concentrations, and shear rates, on the viscosity variations of the reaction systems during the polymerization were studied in detail. Temperature, METAC/lignin molar ratio, and shear rate increases led to the enhanced viscosity of the reaction medium and lignin polymer with a higher degree of polymerization. The extended reaction time enhanced the viscosity attributing to the larger molecular weight of the lignin polymer. Additionally, the size of particles in the reaction system dropped as reaction time was extended. The lignin polymer with a larger molecular weight and Rg behaved mainly as a viscose (tan δ > 1 or G″ > G') material, while the lignin polymer generated with smaller molecular weight and shorter Rg demonstrated strong elastic characteristics with a tan (δ) lower than unity over the frequency range of 0.1-10 rad/s.

pH-responsive SERS substrates based on AgNP-polyMETAC composites on patterned self-assembled monolayers

Patterned silver nanoparticle (NP)-poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (AgNP-polyMETAC) composites were prepared by electrochemical lithography, surface-initiated atom-transfer radical polymerization (SI-ATRP) and NP growth inside the polymer brushes. For this purpose, polymer brushes of poly[2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (polyMETAC) were utilized as strong electrolyte brush system. These were introduced in form of patterned polymer brushes to create pH-responsive surface enhanced Raman scattering SERS substrates. It is well-known that the charges of strong polyelectrolyte chains are usually insensitive to pH changes, hence, rarely strong polyelectrolyte brushes have been utilized so far to study pH-responsive properties of such films. Here pH-insensitive polyMETAC brushes exhibit pH-sensitive properties and can be used as pH-responsive surfaces for SERS applications due to the embedding of AgNPs into the polymer brushes. When increasing the pH, the assembly of the AgNPs transfers from quasi two-dimensional (2D) aggregates, attaching mainly to the polymer surface, into a three-dimensional (3D) assembly, where the particles are penetrating into the brushes. These changes result in significant alterations of the SERS efficiency of the polymer brush composite. At pH 5, the enhancement of the Raman scattering approaches its maximum. The fabricated SERS substrates show a high sensitivity as well as good experimental reliability at different pH values. Moreover, electrochemical lithography was utilized to fabricate patterned SERS substrate, which allows an easy combination of multiple other functionalities in hierarchical structuring steps. In addition, the microstructure is in our studies beneficial because of a simplified and reliable characterization of the polymer brushes at defined sample areas. The introduction of the microstructured brush system is regarded moreover attractive for the development of high-throughput platforms for rapid, automated screening and analysis 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.

Polarity of Cationic Lignin Polymers: Physicochemical Behavior in Aqueous Solutions and Suspensions

The structure of cationic monomers can significantly impact the polarity of lignin after polymerization. Cationic hydrolysis lignin (CHL) polymers were produced by polymerizing hydrolysis lignin (HL) with [3-(methacryloylamino)propyl] trimethylammonium chloride (MAPTAC) or [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (METAC). The METAC monomer has an oxygen atom, with larger electronegativity, in its molecular structure, whereas the MAPTAC monomer contains a nitrogen atom, as well as an extra nonpolar CH₂ group, facilitating investigation into the effects of the polarity of CHLs on their physicochemical performance in an aqueous system. CHL polymers are analyzed and their interactions with clay particles are determined in colloidal systems. CHLs are designed to have similar charge densities (2.1-2.2 mmol g^-1) and molecular weights (55000-60000 g mol^-1 ). The hydrodynamic radius (H_y) and radius of gyration, (R_g) of HL-METAC are larger than those of HL-MAPTAC, implying a more 3-dimensional structure of HL-METAC in aqueous solution. The stability ratio of kaolin particles affirms the better performance of HL-METAC in comparison to HL-MAPTAC, which reflects the better flocculation efficiency of HL-METAC. The results also reveal that salt and urea aqueous solutions affect the H_y, R_g, and configuration of CHL polymers, which alters the flocculation efficiency of HL-METAC and HL-MAPTAC polymers in kaolin suspensions.

Generation and Use of Lignin-g-AMPS in Extended DLVO Theory for Evaluating the Flocculation of Colloidal Particles

In this work, Kraft lignin (KL) was polymerized with 2-acrylamido-2-methylpropane sulfonic acid (AMPS) to generate an anionic water-soluble KL-g-AMPS polymer. The effects of reaction conditions on the charge density of polymers were evaluated to induce lignin-based polymers with the highest anionic charge density. The optimal process conditions were 2.5 mol/mol AMPS/lignin, 0.6 g/g solid/water ratio, 2.0 initiator/lignin weight ratio, 80 °C, 120 min, and pH 1.5, which yielded KL-g-AMPS with the anionic charge density of 4.28 mequiv/g and the grafting ratio of 285%. The chemical structure and compositions of the polymers were confirmed by 1H NMR and elemental analysis. The flocculation performance of the polymer was evaluated in an aluminum oxide suspension, and its performance was compared with that of a homopolymer of AMPS produced under the same conditions. In addition, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to study the flocculation mechanism of the polymers and alumina particles. The results revealed that electrostatic interaction was found to be the dominant force in this flocculation process.

Effects of charge density and molecular weight of papermaking sludge-based flocculant on its decolorization efficiencies

The charge densities (CD) and molecular weights (MW) of the flocculants are closely related to their application performances, but seldom researches focus on the effects of flocculant CD and MW on decolorization efficiencies. Herein, a series of flocculants with various CD and MW levels, named as PBF_1-9, were designed and synthesized from papermaking sludge. The physicochemical characteristics of the PBF_1-9 were measured by fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and particle charge density analyzer (PCD). The efficiencies of PBF_1-9 were studied in the reactive blue (RB) dye removals by flocculation under different process conditions. The operation costs of the flocculants were evaluated at their optimal dosages. Also, the pH-independences and ion-tolerances of the aforementioned flocculants were studied in terms of the molecular levels. The experimental results exhibited that the flocculants CD or MW values were relevant to their flocculation behaviors and operation costs. CD values played a dominant role in color removal efficiencies and the costs, whereas MW values were critical to the floc structure. The pH or ion-independences of the flocculants were significantly dependent on the CD and MW values. However, some conclusions, conflicted with prior studies, were observed in this work. For instance, flocculant with the highest CD and MW levels was not the most effective one in enduring pH variation and the coexisting ions. The floc properties, including floc size, resistance and recovery ability, were relatively insensitive to flocculant intrinsic CD and MW levels when the flocculants were used at their optimal dosages. Furthermore, the possible relevance between CD or MW levels and the flocculation mechanisms have been proposed in this work. Exploring the effects of flocculants CD and MW levels could precisely control the flocculant characteristics to achieve satisfactory decontamination efficiencies with low costs.

High-Performance Flocculants for Purification: Solving the Problem of Waste Incineration Bottom Ash and Unpurified Water

The silicon-aluminum-iron flocculant (PAFSi) combines the most abundant resources of waste incineration bottom ash and unpurified water, being regarded as one of the most promising approaches toward water purification. Herein, in this research, waste incineration bottom ash was employed to produce a cost-effective and highly efficient flocculant. PAFSi with a particle size of 214 nm and a zeta potential of 8.63 mV reached the optimum performance using a dosage of 2 mL/50 mL at pH from 8 to 11. The results with the copolymer exhibited the following: (1) a good flocculation efficiency over a wide pH range, (2) superior flocculation performance compared to those of polyaluminum chloride and polyferric sulfate, (3) three-dimensional branching structure of PAFSi micelles with a high aggregation degree, (4) charge neutralization and bridging as the main flocculation mechanism, and (5) recycling the floc. Thus, this work provides an attractive solution to the pressing global clean water shortage problem.

Phenomenological Changes in Lignin Following Polymerization and Its Effects on Flocculating Clay Particles

Cationic kraft lignin (CKL) macromolecules were produced via polymerizing kraft lignin (KL) with [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATAC) or [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM). Despite slightly different charge densities (2.3-2.5 mmol/g) of CKL, lignin-METAM (KL-METAM) had a significantly larger molecular weight and radius of gyration. A correlation was observed between the structure of CKLs and their impacts on the surface hydrophilicity of kaolin particles. In interacting with kaolin particles, KL-METAM generated larger and stronger flocs with looser structures than did KL-ATAC. Compared to ATAC, METAM had one additional methyl substituent on its structure, which provided fundamental evidence on how a small group (i.e., a methyl group) on the structure of a cationic monomer can have a substantial influence on its polymerization with lignin and subsequently on the efficiency of the induced macromolecule as a flocculant in a kaolin suspension system.

Lignin Biopolymers in the Age of Controlled Polymerization

Polymers made from natural biomass are gaining interest due to the rising environmental concerns and depletion of petrochemical resources. Lignin isolated from lignocellulosic biomass is the second most abundant natural polymer next to cellulose. The paper pulp process produces industrial lignin as a byproduct that is mostly used for energy and has less significant utility in materials applications. High abundance, rich chemical functionalities, CO2 neutrality, reinforcing properties, antioxidant and UV blocking abilities, as well as environmental friendliness, make lignin an interesting substrate for materials and chemical development. However, poor processability, low reactivity, and intrinsic structural heterogeneity limit lignins' polymeric applications in high-performance advanced materials. With the advent of controlled polymerization methods such as ATRP, RAFT, and ADMET, there has been a great interest in academia and industry to make value-added polymeric materials from lignin. This review focuses on recent investigations that utilize controlled polymerization methods to generate novel lignin-based polymeric materials. Polymers developed from lignin-based monomers, various polymer grafting technologies, copolymer properties, and their applications are discussed.

Preparation and optimization photocatalytic activity of polymer-grafted Ag@AgO core-shell quantum dots

A linear-dendric copolymer containing polyethylene glycol-polycitric acid used as a capping agent to the green inter-matrix synthesis of silver/silver oxide core-shell quantum dots (Ag@AgO QDs). Water-soluble Ag@AgO QDs were synthesized with high yield and narrow size distribution. Here, Ag ions were trapped in the polymer branches and covalently bonded to it. Another sample of Ag@AgO QDs was synthesized through the same method and conditions without any capping agent (raw nanoparticles). Structure, size distribution, and morphology of raw and copolymer-grafted nanoparticles were identified using X-Ray diffraction, field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The results from XRD pattern and UV spectra confirmed the Ag@AgO structure of both nanoparticles. From the FESEM image, the size of Ag nanoparticles obtained at the range of 1-20 nm. HRTEM image of grafted nanoparticles directly showed that these nanoparticles have very tiny size in the range of 1-2 nm and presented in the form of core-shell Ag@AgO. Thus, both raw and polymer-grafted samples are in the range of quantum dots (QDs). Raw and polymer-grafted Ag@AgO QDs which take the advantage of water solubility and biosafety, were used as photocatalyst for degradation of cationic methylene blue (MB) and anionic methyl orange (MO) dyes at low and high concentrations of each dye. Results shows using polymer-grafted QDs leads to a significant enhancement both in the efficiency and rate of dye degradation, compared to the case of using raw nanoparticles.

Flocculation of kaolin particles with cationic lignin polymers

Currently, lignin of black liquor is incinerated to generate energy in pulp mills; but it has potential to be valorized through different modification methods. In this work, kraft lignin (KL) was polymerized with 2-[(methacryloyloxy) ethyl] trimethylammonium chloride (DMC) to produce cationic water soluble polymers. After producing five polymers with different molecular weights and charge densities, their flocculation efficiency in kaolin suspensions was investigated. The adsorption, zeta potential and flocculation results confirmed that the polymer with the highest charge density and molecular weight (KLD5) was a more effective flocculant than other polymers. The structure and size of flocs formed from the interaction of kaolin with KLD were determined by a focused beam reflectance measurement (FBRM). The sedimentation studies, conducted under gravitational (by vertical scan analyzer) and centrifugal force (by Lumisizer analytical centrifuge), revealed that KLD5 was very effective in flocculating kaolin particles.

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

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

Lignin-g-poly(acrylamide)-g-poly(diallyldimethyl- ammonium chloride): Synthesis, Characterization and Applications

The search for a renewable substitute to petroleum-based products has fueled increasing research on lignin, an under-utilized product from pulping processes. In this work, lignin was copolymerized with acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) under acidic conditions with Na2S2O8 as an initiator, generating a cationic water-soluble lignin-g-P(AM)-g-P(DADMAC) copolymer. The optimal reaction conditions, using a 5×4 factorial design experiment, were determined to be an AM/DADMAC/lignin molar ratio of 5.5:2.4:1, 90 °C, 0.26 mol L-1 of lignin, and pH 2. Under the optimal reaction conditions, the resulting lignin-g-P(AM)-g-P(DADMAC) copolymer was 83 % soluble in an aqueous solution (at 10 g L-1) and at neutral pH. The copolymer had a charge density of 1.27 meq g-1, molecular weight of (1.33±0.08) ×106, an AM grafting ratio of 112 wt %, and a DADMAC grafting ratio of 20 wt %. In addition, the activation energy for producing this copolymer as well as the thermal and rheological properties of the copolymer were determined. The flocculation performance of lignin-g-P(AM)-g-P(DADMAC) copolymer was evaluated in a kaolin suspension, which showed that the lignin copolymer had a comparable flocculation efficiency with the synthetic analogue of P(AM)-g-P(DADMAC) at pH 6.

Hardwood Kraft Lignin-Based Hydrogels: Production and Performance

In this study, hydrogels were synthesized through the radical polymerization of hardwood kraft lignin, N-isopropylacrylamide, and N,N'-methylenebisacrylamide. Statistical analyses were employed to produce lignin-based hydrogels with the highest yield and swelling capacity. The success of the polymerization reactions was confirmed by NMR and Fourier infrared spectroscopy. The lignin-based hydrogel was more thermally and rheological stable, but exhibited less swelling affinity, than synthetic hydrogel. The rheological studies indicated that the swollen hydrogels were predominantly elastic and exhibited a critical solution temperature that was between 34 and 37 °C. Compared with the synthetic hydrogel, lignin-based hydrogel behaved less elastic as temperature increased. In addition to inducing a green hydrogel, the results confirmed that hardwood lignin-based hydrogel would have different properties than synthetic-based hydrogels, which could be beneficial for some applications.