Lignin has an enormous valorization potential as a sustainable raw material. The most common source of industrial lignin is black liquor, a byproduct from the kraft process. However, the variability in color and chemical characteristics of precipitated lignin is a constituent, hindering its use as a raw material. The structural complexity and heterogeneity of the lignin molecule make it challenging to determine the underlying mechanisms behind the chemical and physical changes that occur during precipitation. This work used a statistical design of experimental approach in Minitab to study how fractionation process variables influence the lignin mass yield and characteristics. The specific phenomena governing hardwood lignin solubility and precipitation in black liquor were investigated, and the relationships between chemical and physical properties and lignin color were analyzed. We found a positive correlation between temperature, mass yield, molecular weight, and dark coloration. For pH < 4, condensation of molecular fragments and sorption onto larger chains seem to drive the precipitation process.

Industry is increasingly turning to biobased and environmentally benign materials for use in high-value applications. Kraft lignin's low cost and inherent properties, such as its easily tunable amphiphilic nature, adsorption capacity, and natural cross-linking tendency, make it suitable for use as a raw material for high-value nanomaterials. To support that need, this paper describes the synthesis of innovative, double-shelled lignin nanocapsules from hardwood kraft lignin, their performance towards encapsulating a fungicide, and effectiveness at controlling its release. The recovered lignin was dissolved without further modification in tetrahydrofuran and inserted dropwise into a water/ethanol solution containing sacrificial surfactant templates. Monodispersed, hollow, double-shell nanocapsules were produced via a two-step self-assembly. The water/ethanol solution acted as a nonsolvent while simultaneously providing strategic sites for controlled-size production. The shells of the nanocapsules were cross-linked with biodegradable maleic anhydride to bolster the structural stability. The average hydrodynamic diameter of the particles was 241.8 ± 33.3 nm, and these structures were stable in water for a period of eight months. The specific surface area of kraft lignin increased by 4-fold in the double-shell nanocapsule form. The nanocapsules were loaded with propiconazole at an entrapment efficiency of 56.1%. This system could represent an effective method to enable biologically activated, controlled release of fungicides.

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.

In the modern forest industry, the need for bio-based, renewable, and environmentally-benign wood preservatives is increasing. The world harvests approximately 1700 million m 3 of wood annually for use in a variety of applications. Unfortunately, when exposed to moisture, wood products are at high risk of decay by wood degrading fungi. Preservatives are used to prevent or limit decay, and there has been an increasing interest in developing wood preservatives from renewable materials. For this work, the effectiveness of water-dispersible, double-shell, lignin nanocapsules encapsulating the fungicide propiconazole, as a sustainable wood preservative, was evaluated. The system was tested for its biocidal efficacy against brown rot decay by Gloeophyllum trabeum in southern yellow pine wood using both dip and pressure treatments. The preservative successfully penetrated the wood block during pressure treatment, and following 3 months of soil-jar incubation, only wood blocks pressure-treated with either the double-shelled-propiconazole nanocapsule system or the conventional exterior wood preservative, chromated copper arsenate (CCA), showed less weight loss (19.95 ± 2.05 and 16.40 ± 3.80%, respectively) compared to the control (41.58 ± 9.51%). Additionally, the novel preservative system exhibited enhanced antifungal resistance compared to its individual constituents, as confirmed with Kirby−Bauer disk diffusion tests. The double-shell lignin nanocapsule exhibited radical quenching activity against DPPH of 75.9 ± 4.2%, and this could have contributed to the enhanced antifungal activity of the double-shell lignin nanocapsule−propiconazole system. This novel preservative system can be considered as a potential bio-based antifungal wood preservative.

No abstract