A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

Abstract

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas.

Enzyme Catalyzed Copolymerization of Lignosulfonates for Hydrophobic Coatings

“…It is known that hydrophobic moieties, when brought into an aqueous milieu, tend to organize in a way that they point into the center of bigger molecules. The same was found for LS in aqueous solutions (Ruwoldt, 2020). While the WCA depends on the presence of hydrophobic molecules on the surface only, the swelling also depends on the internal structure of the polymers (Bracco and Holst, 2013;Thakur et al, 2017).…”

“…First, this sounds like the reactivity should increase, but in fact, it hinders the interaction between enzyme and LS due to increased electrostatic repulsion and a further decrease of enzyme activity with increasing pH at the same time. Also, hydroxide anions are known to inhibit laccase activity at high pH (Xu, 1997;Morozova et al, 2007;Vernekar, 2014;Singh, 2016;Ruwoldt, 2020). Based on these findings all following experiments were carried out at pH 7.…”

Nano-Structured Lignin as Green Antioxidant and UV Shielding Ingredient for Sunscreen Applications

“…Lignin is considered an amphipathic polymer due to the presence of both hydrophilic and hydrophobic components. In addition, the presence of ionizable groups make it an efficient stabilizer by the occurrence of electrical repulsion effects [ 146 ]. A case of study for the application of LNPs as a stabilizer is represented by the production of Pickering emulsions, which were characterized by a higher deformation resistance compared to that stabilized with conventional surfactants.…”

Lignosulphonates as an Alternative to Non-Renewable Binders in Wood-Based Materials

“…Some studies have achieved accurate results with in-line multi-angle laser light scattering (MALLS). This system solved previous problems caused by unrepresentative calibration standards, variations in refractive index, and fluorescence [45]. The complex mobile phase used by Fredheim and co-workers was chosen in order to prevent formation of aggregates and absorption to the column material [43,46].…”