Functionalized lignin biomaterials for enhancing optical properties and cellular interactions of dyes

Structure and properties of nanoparticles: DES-lignin-g-PNVCL coated aspirin by self-assembly

This work was carried out in order to broaden the application field of lignin and improve its additional value. The degraded deep eutectic solvent lignin-grafted poly(N-vinyl caprolactam) (DES-lignin-g-PNVCL) was synthesized by using modified DES-lignin and NVCL via activators regenerated by electron transfer-atom transfer radical polymerization (ARGET-ATRP). Aspirin was coated with DES-lignin-g-PNVCL through self-assembly by an ethanol/water anti-solvent method to obtain lignin thermosensitive polymer nanoparticle coated aspirin (aspirin@LTNP). X-ray electron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and ultraviolet visible spectroscopy (UV) were used to characterize the composition, structure and morphology of DES-lignin-g-PNVCL and aspirin@LTNP. The releasing behavior of aspirin@LTNP at different temperatures and pH values was investigated. The safety was evaluated by cytotoxicity tests. The results indicated that aspirin@LTNP was mainly accumulated by the hydrophobic effect and π-π interaction in the process of self-assembly, and its morphology was an ellipsoid stacked layer by layer. The aspirin@LTNP hydrophilic chains were increased and had externally hydrophilic and internally hydrophobic structures. The particle size decreased slightly during the self-assembly process. The red-shift occurred at the π-π interaction wavelength of the lignin aromatic ring, which indicated a physical coating process. The coating rate of aspirin@LTNP was 88.87%. Aspirin@LTNP showed an obvious temperature response; the 96 h cumulative release rate at the LCST was 73.75 ± 1.16%, while the 96 h cumulative release rate above the LCST was 28.10 ± 0.92%. The 96 h cumulative release rate was 63.21 ± 0.57% at pH = 1.5 and 49.56 ± 0.48% at pH = 7.4. The dosage of aspirin@LTNP used in the experiment was safe. This study provided a strategy for drug coating and controlled release.

Hydrothermal method-assisted synthesis of self-crosslinked all-lignin-based hydrogels

Lignin, as the most abundant aromatic biopolymer, is being widely studied to replace phenol and some other petroleum-based materials in the polymer industry. However, the low substitution of lignin and high levels of additives greatly limited the applications of lignin-based materials. Herein, we first propose a simple but effective hydrothermal method assisted synthesis for the fabrication of self-crosslinked lignin-based hydrogels (Lig-Scgel) with super-high-contents (75 wt%) of lignin and controllable mechanical properties. The self-crosslink mechanism was inspired by the repolymerization of lignins under a hydrothermal environment. The employment of self-condensation of lignin subunits in the synthesis of Lig-Scgel can significantly improve the degree of crosslinking, thereby greatly reducing the addition of toxic crosslinkers. The appearances, microstructures, crosslink densities, and mechanical properties of Lig-Scgels can be well controlled by simply altering the hydrothermal temperatures. This strategy not only promotes green and large-scale applications of lignin but also provides insights in the development of environment-friendly polymeric materials.

Promoting Interfacial Interactions with the Addition of Lignin in Poly(Lactic Acid) Hybrid Nanocomposites

In this paper, the calorimetric response of the amorphous phase was examined in hybrid nanocomposites which were prepared thanks to a facile synthetic route, by adding reduced graphene oxide (rGO), Cloisite 30B (C30B), or multiwalled carbon nanotubes (MWCNT) to lignin-filled poly(lactic acid) (PLA). The dispersion of both lignin and nanofillers was successful, according to a field-emission scanning-electron microscopy (FESEM) analysis. Lignin alone essentially acted as a crystallization retardant for PLA, and the nanocomposites shared this feature, except when MWCNT was used as nanofiller. All systems exhibiting a curtailed crystallization also showed better thermal stability than neat PLA, as assessed from thermogravimetric measurements. As a consequence of favorable interactions between the PLA matrix, lignin, and the nanofillers, homogeneous dispersion or exfoliation was assumed in amorphous samples from the increase of the cooperative rearranging region (CRR) size, being even more remarkable when increasing the lignin content. The amorphous nanocomposites showed a signature of successful filler inclusion, since no rigid amorphous fraction (RAF) was reported at the filler/matrix interface. Finally, the nanocomposites were crystallized up to their maximum extent from the glassy state in nonisothermal conditions. Despite similar degrees of crystallinity and RAF, significant variations in the CRR size were observed among samples, revealing different levels of mobility constraining in the amorphous phase, probably linked to a filler-dimension dependence of space filling.

UV-protection from chitosan derivatized lignin multilayer thin film

Lignin is one of the most abundant renewable materials on the earth. Despite possessing useful antioxidant and UV absorbing properties, its effective utilization in technology has been hampered by its relative insolubility and difficulty to process. In this work, a simple chemical derivatization process is utilized which yields water-soluble lignin possessing anionic carboxylate groups. These carboxylate groups give lignin polyanionic behavior and enable its utilization in the growth of a functional film via layer-by-layer (LbL) assembly with biologically sourced chitosan. The growth mechanism of this film is hypothesized to be a result of both hydrogen bonding and ionic interactions. The film demonstrates excellent UV-absorptive capability. A 100 nm thick chitosan/lignin coating was applied to a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and shown to reduce its degradation sixfold over the course of a 1 hour exposure to harsh UV light. This is the first demonstration of lignin being utilized in a fully biologically derived LbL film. Utilization of lignin in LbL assembly is an important step in the development of renewable nanotechnology.

An environmentally benign derivatization process enables the use of lignin in an entirely biosourced functional thin film.

The Self-Assembly of Lignin and Its Application in Nanoparticle Synthesis: A Short Review

Lignin serves as a significant contributor to the natural stock of non-fossilized carbon, second only to cellulose in the biosphere. In this review article, we focus on the self-assembly properties of lignin and their contribution to its effective utilization and valorization. Traditionally, investigations on self-assembly properties of lignin have aimed at understanding the lignification process of the cell wall and using it for efficient delignification for commercial purposes. In recent years (mainly the last three years), an increased number of attempts and reports of technical-lignin nanostructure synthesis with controlled particle size and morphology have been published. This has renewed the interests in the self-assembly properties of technical lignins and their possible applications. Based on the sources and processing methods of lignin, there are significant differences between its structure and properties, which is the primary obstacle in the generalized understanding of the lignin structure and the lignification process occurring within cell walls. The reported studies are also specific to source and processing methods. This work has been divided into two parts. In the first part, the aggregation propensity of lignin based on type, source and extraction method, temperature, and pH of solution is discussed. This is followed by a critical overview of non-covalent interactions and their contribution to the self-associative properties of lignin. The role of self-assembly towards the understanding of xylogenesis and nanoparticle synthesis is also discussed. A particular emphasis is placed on the interaction and forces involved that are used to explain the self-association of lignin.

Functionalized Tyrosinase-Lignin Nanoparticles as Sustainable Catalysts for the Oxidation of Phenols

Sustainable catalysts for the oxidation of phenol derivatives under environmentally friendly conditions were prepared by the functionalization of lignin nanoparticles with tyrosinase. Lignin, the most abundant polyphenol in nature, is the main byproduct in the pulp and paper manufacturing industry and biorefinery. Tyrosinase has been immobilized by direct adsorption, encapsulation, and layer-by-layer deposition, with or without glutaraldehyde reticulation. Lignin nanoparticles were found to be stable to the tyrosinase activity. After the enzyme immobilization, they showed a moderate to high catalytic effect in the synthesis of catechol derivatives, with the efficacy of the catalyst being dependent on the specific immobilization procedures.