Preparation and Formation Mechanism of Covalent–Noncovalent Forces Stabilizing Lignin Nanospheres and Their Application in Superhydrophobic and Carbon Materials

Abstract

Self-assembled lignin nanospheres (LNS) have attracted much attention due to the new opportunities provided for the preparation of value-added products derived from lignin. However, the internal connections of the LNS generally depend on weak intermolecular forces, leading to low solubility resistance and thermostability. In this study, we present a simple method for the fabrication of covalent–noncovalent forces stabilizing lignin nanospheres (HT-LNS) through utilizing the natural characteristic that lignin molecules undergo irreversible condensation under high-temperature stimulation. Experiments demonstrated that the action of temperature resulted in the fracture of β-O-4 ether and Cα–Cβ bonds, as well as hydroxyl and −OCH3 lignin molecule groups, leading to the formation of free radicals in the LNS. In addition, a large number of adjacent intramolecular and intermolecular radicals almost simultaneously generated chemical cross-linking via α-5, β-5, β–β′ bonds, and so forth. The amount of lignin molecules participating in the cross-linking reaction increased with temperature, which gradually reduced the HT-LNS diameter from 597 to 477 nm and enhanced the maximum decomposition peak from 367.7 to 395.1 °C. The solubility of nanospheres in ethanol and tetrahydrofuran (THF) decreased from 93.92 to 10.39% and from 98.09 to 22.45% with increasing treatment temperature, respectively. The HT-LNS can be employed in the preparation of superhydrophobic coatings, replacing non-environmentally friendly silica nanoparticles. The water contact and slide angles were determined as 151.9 ± 1.4 and 9.4 ± 0.5°, respectively. Moreover, the application of HT-LNS for the preparation of lignin-based carbon nanospheres maintained a perfect spherical structure with tiny graphitic area and the content of carbon atoms reached up to 94.99%. This study provides a simple and effective technology platform for the development of green materials.

Novel lignin microspheres reinforced poly (lactic acid) composites for fused deposition modeling

“…The result showed that the contact and sliding angles of the prepared coatings were determined to be 151.9 ± 1.4° and 9.4 ± 0.5°, respectively, which could be used as a substitute for non‐environmentally friendly silica nanoparticles. [ 15 ] Paul et al used lignin nanospheres for nano‐spray (LNSR), which exhibited excellent UV‐blocking, antioxidant, and photo‐activated antibacterial properties. [ 16 ] Bai et al used lignin microspheres as Pickering emulsifiers to stabilize oil‐in‐water (O/W) emulsions, which typically showed longer service life compared to surfactant‐based emulsions, as well as enhanced properties of Pickering emulsions such as sunscreen, antioxidants, and antimicrobial activity.…”

A Rapid and Reversible pH Control Process for the Formation and Dissociation of Lignin Nanoparticles

“…[12a] Wang et al prepared LNPs with the maximum concentration of 0.4 g L À 1 by tetrahydrofuran/water solvent exchange system. [13] However, the high consumption of solvents and the low concentration of product significantly increased the costs of the production and limited the application of LNPs. Although spray drying and a few cosolvent approaches can prepare LNPs with higher concentrations, [5b,14] the uniformity, stability, and regenerability of LNPs also limited their large-scale applications.…”

“…Wang et al. prepared LNPs with the maximum concentration of 0.4 g L −1 by tetrahydrofuran/water solvent exchange system [13] . However, the high consumption of solvents and the low concentration of product significantly increased the costs of the production and limited the application of LNPs.…”

Fluorescent solvent-free lignin ionic complexes with thermostability toward a luminescent hydrophobic coating material

“…Lignin, one of the most abundant renewable bioresources, is a phenylpropane unit-rich amorphous polymer. 1,2 However, the practical application of lignin is way more difficult, owing to its irregular structure with aromatic rings. 3 Aiming at facilitating the application of lignin, various methodologies have been develop in this field; for example, fluorescence lifetime imaging microscopy is used for analyzing the chemical composition of natural lignin 4 and multicopper laccase-mimicking nanozymes of Cu/GMP is developed for lignin degradation.…”

“…8 In recent studies, based on the AIE theory the development of fluorescent lignin materials is gaining increasing attention, mainly focusing on the preparation of nanoparticles and nanospheres, which provide opportunities for value-added utilization of lignin. 2,3,[8][9][10][11] In the developed lignin nanomaterials, the aggregated state restricts the intramolecular motions, causing fluorescence emission by blocking the non-radiative decay channel. Meanwhile, for such nanomaterials the following considerations should be noticed: (1) the presence of solvents or polymeric networks is required for the successful fluorescence emission by regulating the assembly state of lignin and other components; otherwise, the aggregation-caused quenching (ACQ) effect would happen; 8,12 (2) the dispersed nanoparticles in solvents are sensitive to temperature, showing poor thermostability of the fluorescent properties at high temperatures.…”