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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]

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]

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]

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]