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Lignin has been produced in large quantities in the pulp manufacturing process; however, its valorization has been challenging. The production of lignin polymers has shown pathways to produce water soluble products to be used as flocculants and dispersants. However, these lignin-based polymers may interact with each other and form large flocs that could reduce their efficiency in interacting with other colloidal particles. This study aims at evaluating the self-assembly of kraft lignin-acrylamide polymers in aqueous environments under different salt concentrations. The sedimentation studies using a vertical scan analyzer showed that a higher molecular weight lignin polymer had a higher tendency for sedimentation than a lower molecular weight one. Quartz crystal microbalance with dissipation (QCM-D) was used for studying the self-assembly behavior of lignin polymers with different molecular weights. The results suggested that lignin polymer with the higher molecular weight of 96,992 g/mol had a higher tendency to self-assemble by forming a loose floc as compared to that with a lower molecular weight. Also, salt disrupted the self-assembly of lignin polymers greatly. [ABSTRACT FROM AUTHOR]

To generate effective dispersants for kaolin suspensions, it is important to study how the properties of dispersants affect their performance in suspensions. In this work, kraft lignin was modified via oxidation with nitric acid under varied conditions to produce oxidized lignin (OL) with different charge densities and molecular weights. The effects of anionic charge density and molecular weight of the lignin based products on the dispersion and sedimentation of kaolin particles were studied fundamentally. The adsorption of OLs on particles as well as the changes in the zeta potential, relative turbidity, hydrodynamic diameter and sedimentation of particles under static (non-stirring) and dynamic (stirring) conditions were systematically investigated. Dispersion studies suggested that both charge density and molecular weight had great impacts on the stability of kaolin particles. Sample OL8 with the charge density of −3.6 meq/g and molecular weight (Mw) of 30,243 g/mol was the most effective dispersant for kaolin suspension. The hydrophilicity of OLs were similar and thus did not affect the dispersion analysis. [ABSTRACT FROM AUTHOR]

In this work, the influence of pH and ionic strength on the flocculation performance of cationic xylan copolymer in kaolin and bentonite suspensions was systematically investigated. The cationic xylan was produced via copolymerizing xylan with 2-(methacryloyloxy ethyl) trimethylammonium chloride (METAC), and the cationic xylan copolymer (CMX) showed a maximum adsorption of 4.6 and 1.8 mg/g on kaolin and bentonite particles at the CMX dosage of 8 mg/g, pH 10, 30 °C and 1 h, respectively. The reduction in charge density of CMX from 2.66 to 2.48 meq/g was observed, with an increase in pH of CMX solution to from 2 to 10. The maximum increase in the zeta potential of kaolin (+54 mV) and bentonite (−3 mV) suspensions and the highest removal of kaolin (75%) and bentonite (96%) from the suspensions were obtained at 8 mg/g CMX and pH 7. Stability studies revealed that pH had a noticeable influence on the sedimentation of kaolin and bentonite particles. CMX increased the destabilization index of kaolin (0.4–45) and bentonite (0.2–51) suspensions by increasing the floc size of kaolin and bentonite particles to 9.5 μm and 12.7 μm, respectively. CMX removed more of bentonite than kaolin at any pH under static and dynamic conditions. The impact of inorganic salts on the removal of kaolin particles was also studied. CMX exhibited better performance than a commercial flocculant (PDADMAC) in flocculating the commercially produced effluent. [ABSTRACT FROM AUTHOR]

A mathematical model was created based on surface element integral (SEI) and XDLVO theory for assessing the interfacial interaction between rough spherical surfaces with random topographies, which were generated following a modified two-variable Weierstrass-Mandelbrot (WM) function. The surface construction and interfacial interaction equations used in this study facilitated the generation of randomly rough spherical surfaces, which assisted in improving the prediction accuracy of particle interactions for natural colloidal particles. This modeling study presented discussions on the interaction of rough surfaces having different asperity heights, asperity positions, random landscape, and roughness in colloidal systems. We observed that the asperity number and ratio were primary parameters for influencing the interfacial interaction between spherical surfaces. The arrangement and randomness in the position of asperities on the surface had negligible effects on the interfacial interaction. The elevated asperity height, as a result of increased fractal roughness or relative fractal roughness on spherical surfaces, could hamper the interfacial energy between surfaces. However, increasing the fractal dimension and relative fractal dimension generated smoother surfaces and thus elevated the interfacial energy developed between surfaces. The most impactful parameter of surface morphologies in altering interfacial energy was fractal dimension as it could control the asperity height and asperity number simultaneously. The largest primary maximum was predicted (216 kT) when the fractal dimension was 2.43, which represented the strongest stability of particles in a suspension. [Display omitted] • Surfaces with altered topographies were generated via surface element integral and XDLVO theory. • Asperity number and ratio were main parameters affecting the interaction between surfaces. • Arrangement and randomness in the position of asperities had minimal effect on the interaction. • Fractal roughness and relative fractal roughness hampered interfacial energy between surfaces. • Fractal dimension and relative fractal dimension elevated interfacial energy between surfaces. [ABSTRACT FROM AUTHOR]

Cationic kraft lignin (CKL) polymers with different degrees of grafting (35.2–125.5 mol%) were synthesized via polymerizing kraft lignin (KL) and [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATAC) or [2 (methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM) to investigate the impact of the chain extension of the polymers on the physicochemical behavior of CKL in an aqueous solution. It was observed that, at the same grafting ratio, the structural difference of CKLs influenced their hydrophilicity, in which the contact angle of KL-METAM and KL-ATAC solution (1 g/L) reached 9.4° and 11.8° on a glass slide, respectively, at the maximum degree of grafting of ~125 mol%. KL-METAM had a more three-dimensional and flexible structure than KL-ATAC in solution, which promoted its self-assembly (with the aggregate diameter of 235–532 nm) and sedimentation (with the TSI value of 16.8). The rheological studies confirmed the more elasticity of KL-METAM than KL-ATAC with the elastic modulus of 9.3 and 8 Pa at the highest frequency. Quartz crystal microbalance (QCM) adsorption studies illustrated that KL-METAM adsorbed more greatly and generated a bulkier and more viscoelastic adlayer than KL-ATAC did on a rigid surface, below saturation (ΔD/Δf slope of 0.13–0.45) and at equilibrium (ΔD/Δf slope of 0.02–0.17). For the deposited adlayer, the alterations in the slope of dissipation/frequency (ΔD/Δf) between the early and late stages of adsorption were claimed to be related to the conformational changes of CKLs upon adsorption. The findings of this study showed that the architecture of cationic monomers could affect the structure of CKLs so significantly that the lignin polymers would have different chain conformations and flexibility in solution, varied rheological properties, and adsorption performance on a solid surface. The significance of the monomer architecture on the properties and performance of CKLs was more observable at a higher grafting ratio. [Display omitted] [ABSTRACT FROM AUTHOR]

Modeling rough surfaces has received attention as it can facilitate understanding of colloidal systems. This work comprehensively discussed a facile approach for simulating the surface morphologies of ellipsoidal particles and membrane surfaces three-dimensionally. The fractal geometry theory was applied to construct a randomly rough surface. The assessment approach involving the surface element integral (SEI) method based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was proposed to quantify the interfacial interaction between the constructed ellipsoidal particle and membrane surface. The simulated results demonstrated that the total interaction energy created between the particle and membrane surface was intensified by enlarging the particle and elevating the fractal dimension of the surface. The fractal roughness and orientation angle of the particle negatively affected the total interfacial energy between the particle and membrane surface. Moreover, the shape of the particle was found to have a profound effect on the total interaction energy. The new method has a wide range of potential applications in membrane bioreactor design and operation since it can predict the interaction of sludge flocs and membrane surface. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, sulfomethylated softwood kraft lignin (OSKL) was prepared by oxidation with nitric acid and sulfomethylation. The product was then used as an anionic flocculant for removing a cationic dye from a simulated dye solution. The present study showed that the efficiency of OSKL was improved with the increment in the charge density of OSKL. The formation of dye/lignin complexes in solution and the precipitation of formed complexes were evident in this work. Based on charge neutralization, the experimental and theoretical amounts required for removing the dye were determined, and the results were compared. The results showed that the pH of the dye solution affected the chemical oxygen demand (COD) removal from the solution, as well as the hydrodynamic diameters of OSKL in solutions. Under the optimal conditions of 300 mg/L of dye, pH 9 and room temperature, 300 mg/L of OSKL was sufficient for removing 99.1% of dye and 90% of COD from the solution. The analysis also confirmed that inorganic salts decreased the efficiency of OSKL in removing dye and time extension to 2 h improved the dye removal. [ABSTRACT FROM AUTHOR]

Lignin is an abundant macromolecule available in large quantities in the world, but it is under-utilized. In this study, lignin was modified via methylation and grafting with dodecyl glycidyl ether (DGE), and films containing these lignin derivatives were generated following different routes and using solvents (water, ammonium hydroxide, and dimethylformamide). The impact of the solvent type, coating method, and temperature on the characteristics of the prepared films was studied using contact angle (sessile drop experiment), scanning electron microscopy, and Turbiscan stability index (TSI) analyses. Methylation and the subsequent DGE grafting improved the hydrophobicity of lignin by blocking the phenolic active site of lignin, which improved the surface tension, contact angle, and interfacial tension of solvents containing lignin derivatives. Such alternations in the hydrophobicity of lignin substantially decreased the water uptake (90 %) of the lignin derivatives analyzed by the powder test wettability analysis. Quartz crystal microbalance (QCM) analysis revealed that the modifications were successful in reducing the dissolution of lignin derivatives in water, and exhibited the fundamental absorption behavior of water by the films. The methylated and DGE grafted lignin derivative with the highest hydrophobicity may be more attractive than other lignin derivatives to be used potentially in coating and packaging applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Flocculation is a widely used method to treat wastewater effluents. Aluminum oxide particles have been recognized as major parts of effluents of ceramic industries. In this work, the flocculation of aluminum oxide particles with various sizes (0.06-0.6 μm) was analyzed using poly(acrylic acid) (PAA) to investigate how the flocculation effectiveness of PAA would be affected by the particle size of aluminum oxides. The zeta potential of the suspensions was changed to a similar extent by PAA, regardless of aluminum oxide particle size, implying that the diffuse double layer of the particles was affected in a similar manner despite different adsorption amounts of PAA. The relative turbidity of the suspensions was remarkably reduced for the aluminum oxide with the largest particle size (AL1) and was less affected by aluminum oxide with smaller sizes (AL3). The chord length of the produced flocs was pronouncedly increased by increasing the particle size of aluminum oxide and the floc counts was reduced substantially. The sedimentation studies of the suspensions revealed more efficient sedimentation behavior for AL1/PAA flocs than for AL1 and AL3 based flocs. The settling velocity and sedimentation compactness of the flocs were also analyzed in this study. [ABSTRACT FROM AUTHOR]

The flocculation process is widely used for separating particles from suspension systems. To make this process more environmentally friendly, a biobased flocculant was proposed to be used in this work. This study involves the experimental evaluation of a flocculation system of aluminum oxide particles (with two different sizes) and a kraft lignin-acrylic acid (KL-AA) polymer, as a biobased-flocculant, with advanced tools, such as focused beam reflectance measurement, vertical scanning analyzer, and gravitational scanning analyzer. A statistical framework was adapted to model the experimental results based on the mixture distribution theory, which led to a more in-depth analysis of the shape and size of flocs in the heterogeneous suspension system. The results revealed that the flocculation process of aluminum oxide suspension was altered by the salinity of the medium as well as the size of aluminum oxide particles. It was found that the flocs formed with KL-AA at a higher NaCl concentration had smaller sizes and exhibited higher shear resistance than the flocs formed in the absence of salt. Furthermore, by increasing the concentration of NaCl, the particles tended to possess more spherical shapes. The results also showed that the fractal dimension for flocculated particles increased by concentrating NaCl in the suspensions. Under gravity and centrifugal forces, the impact of KL-AA in flocculating particles was insignificant in the presence of salt. [Display omitted] • Lignin-acrylic acid flocculant was used for treating aluminum oxide suspensions. • Experimental and modeling results confirmed the smaller flocs in saline systems. • The larger particles flocculated and settled faster and generated larger and bulkier flocs. • De-flocculation and re-flocculation of flocs were investigated at different salinity. • The impact of flocculant was less observed in saline system under gravitational forces. [ABSTRACT FROM AUTHOR]