Lignin Nanoparticle Morphology Depends on Polymer Properties and Solvent Composition: an Experimental and Computational Study

Abstract

Kraft lignin is an underutilized sideproduct from the pulp and paper industry that can be used as a feedstock for various bio-based products. In particular, microstructured lignin particles are used as functionalized materials in applications such as the controlled release of active substances and the absorption of contaminants and as polymer additives. Gaps in our understanding of lignin molecular interactions and morphology in various solvents limit our ability to tailor processes to produce particles with desired properties. We empirically demonstrate that the dispersity and aqueous phase polarizability influence lignin polymer chain conformation and thus the resulting nanoparticle morphology. Our complementary experimental and computational studies investigate lignin dynamics and indicate that a high molar mass polymer with a low polydispersity index, which contains numerous aromatic structures, will aggregate via hydrophobic interactions and form compact globules in an aqueous environment. Even in the presence of a sacrificial negatively charged surfactant sodium dodecyl sulfate, electronic interactions of aromatic units predominate, resulting in a compact globule after the surfactant is removed. Additionally, the number of inter-lignin contacts, solvent−polymer hydrogen bonds, and radius of gyration for a high molar mass, low polydispersity index lignin polymer remained almost constant in water and in the mixed (water/ethanol) solvent system containing the surfactant. We also report dendritic lignin nanoparticles obtained experimentally from low molar mass, high polydispersity index lignin, in a water/ethanol mixed aqueous phase. Molecular simulation results suggest that the intermolecular forces driving this morphology are stable inter-lignin contacts over time and enhanced lignin-solvent hydrogen bonding in the mixed solvent. Our results demonstrate the controlled behavior of lignin nanoparticle morphologies in aqueous solvents. This work contributes toward establishing property−performance correlations for lignin and advances knowledge for the synthesis of shape-specific lignin nanoparticles.

Lignin Smart Nanoparticles for Effective and Eco-Friendly Resource Recovery from Wastewater: Status, Challenges, and Opportunities

“…40 Furthermore, hydrophobic chains tend to render particles with smaller diameters. 37 On the contrary, a higher concentration of hydroxyl groups introduces hollows in the nanoparticle and can increase the hydrodynamic diameter of the nanoparticle. 37 Observing the work by Pylypchuck et al 121 presented on the first row of Table 5, the zeta potential of the nanoparticles made from lower molecular weight precursors are higher; inversely, their hydrodynamic diameters are larger.…”

“…37 On the contrary, a higher concentration of hydroxyl groups introduces hollows in the nanoparticle and can increase the hydrodynamic diameter of the nanoparticle. 37 Observing the work by Pylypchuck et al 121 presented on the first row of Table 5, the zeta potential of the nanoparticles made from lower molecular weight precursors are higher; inversely, their hydrodynamic diameters are larger. On the other hand, there is no direct correlation between the concentration of hydroxyl groups and the size and zeta potential of the nanoparticles.…”

“…45 The primary benefits of employing surfactants during nanoparticle synthesis have been reported as reducing the surface tension, 143 homogenizing and tuning the particle size, promoting shape uniformity, and providing an avenue to control the morphology and physicochemical properties of the resultant nanoparticles. 37 Tang et al 143 employed the positively charged surfactant cetyltrimethylammonium bromide to neutralize the surface charge of hydrophilic sodium lignosulfonate in order to form colloidal lignin nanoparticles via hydrophobic selfassembly in a solvent−antisolvent system. They dissolved lignin and cetyltrimethylammonium bromide (at a stoichiometric mass ratio of lignin:surfactant = 1:2.82) in ethanol and gradually added water to the system, noting that molecule aggregation commenced at 58 % (v/v) water and concluded at 84 % water in the system (Figure 6).…”

Atomistic Modeling of Lignocellulosic and Carbonaceous Fuels and Their Pyrolysis Reactions: A Review

“…Lignin Builder is another robust tool that can be used to construct lignin structures and study interaction with other components (Figure b) . Many authors have used this software to model lignin structures and understand their properties and behavior. − …”

Atomistic Simulations of Polydisperse Lignin Melts Using Simple Polydisperse Residue Input Generator

“…Except for the models generated by Broadbelt’s group, , other common tools for lignin topology generation do not explicitly set a given polydispersity by default. While specific lignins can be selected from a pool of generated lignins to achieve a specific polydispersity, this posthoc processing can alter other desired lignin properties, such as the S:G ratio or the linkage distribution. The resulting differences between the plant-based experimental and theoretical literature are an impediment to direct comparison with experimental measurements on cell wall lignins.…”