Interfacial and Emulsion Characteristics of Oil–Water Systems in the Presence of Polymeric Lignin Surfactant

Abstract

It is hypothesized that polymeric lignin surfactants have different affinities for stabilizing oil–water emulsions and that the emulsifying performance of these surfactants is highly affected by their adsorption performance at the oil–water interface. To validate this hypothesis, the adsorption performance of sulfethylated lignin (SEKL) surfactant at different oil–water interfaces was examined by assessing the contact angle, dynamic interfacial tension, and surface loading (Γ). Moreover, the interfacial adsorption kinetics of SEKL was comprehensively assessed in different oil–water systems to reveal the mechanisms of the SEKL adsorption at the interface. Also, the impacts of SEKL concentration and ionic strength on the performance of SEKL as an effective emulsifier for the emulsions were assessed. Furthermore, the droplet size and instability index of the emulsions were systematically correlated with the adsorption performance of SEKL at the interface of oil and water. For the first time, by implementing a modified Ward Toradai diffusion model, two distinct early stages of the adsorption of SEKL at the oil interface were identified. Interestingly, the second stage was the determining stage of adsorption with the diffusion-controlled mechanism when polymers reconfigured at the oil–water interface. Salt screening facilitated the clustering of SEKL upon charge repulsion elimination, which removed the energy barrier in the first stage of adsorption (ΔE p →0 = 0), but it introduced a steric barrier upon the reconfiguration of polymers at the oil interfaces in the second stage of adsorption. In addition to the kinetics of adsorption, satisfactory correlations were observed between surface pressure (Δγ = γ∞ – γ0), surface loading (Γ) of polymers, and contact angle at oil interfaces on one hand and the oil droplet size and emulsion stability on the other hand.

Extraction and Surfactant Properties of Glyoxylic Acid‐Functionalized Lignin

“…[15,16] To increase the properties of lignin as surfactant, chemical modification is consequently often necessary to introduce better hydrophilic groups along the polymer chains. [17] For instance, reactions of sulfethylation, [18] esterification, [19] etherification, [20] as well as grafting through reversible additionfragmentation chain-transfer (RAFT) polymerization [21] have been carried out on lignin oligomers to explore their further use as surfactants.…”

Recent Studies on the Preparation and Application of Ionic Amphiphilic Lignin: A Comprehensive Review

“…The results of this study also preliminarily clarified the interfacial behavior and adsorption mechanism of the sulfonated lignin-based surfactant at the oil−water interface. 56 2.2. Cationic Amphoteric Lignin Polymers.…”

Recent Developments in the Formulation and Use of Polymers and Particles of Plant‐based Origin for Emulsion Stabilizations

“…The anionic derivatives of lignin, such as carboxyalkylated, [166–168] sulfoalkylated, [169] and acylated lignin, [170] were reported as effective emulsifiers to increase the interfacial activity of lignin. The mutual trend was a decline in surface and interfacial tension with the polar groups, as was reported for carboxymethylated lignin (CML), which was further decreased by increasing the DS of CML, [167] lignin‐tannic acid (KL‐TA), [168] and sulfoethylated lignin (SE‐KL) derivatives [169] . The stabilized emulsion with carboxyalkylated and sulfonated lignin derivatives showed pH‐responsive performance.…”

“…For both OSA‐CFG (octenyl succinic anhydride‐modified corn fibre gum) and N‐SEKL systems, the diffusion of polymers to the oil/water interface occurred in the emulsion interface. The formation of the interfacial layer at oil/water interfaces followed by the reconfiguration of hydrophobic segments in the oil phase and diffusion of the hydrophilic fragments into the water phase provided a steric hindrance [136,169] …”