Influence of Carbohydrates Covalently Bonded with Lignin on Solvent Fractionation, Thermal Properties, and Nanoparticle Formation of Lignin

Abstract

The valorization of industrial lignin essentially requires fractionation resulting in lower structural heterogeneity and polydispersity. So far, extensive fractionation approaches based on extraction with solvents, gradient acid precipitation, and membrane-based filtration have been developed to reduce the polydispersity and heterogeneity of technical lignins. However, most reports tend to overlook the lignin fraction that bonded with carbohydrates or the so-called lignin carbohydrate complex (LCC), which always coexists in the initial lignin sample and can significantly affect the properties of lignin, including its homogeneity and solubility. In this study, we evaluated the ability of 13 organic solvents to separate lignin bonded with carbohydrates. It was found that carbohydrates could only be detected when the hydrogen bonding capacity (δH) of solvent was no less than 8.0 (the δH of tetrahydrofuran, THF). Based on this result, eight lignin fractions with trace/large amounts of carbohydrates and decreased heterogeneity were obtained using an elaborate sequential solvent extraction approach. The following properties of each lignin fraction were compared: elemental composition, carbohydrate content, molar mass, hydroxyl group content, and thermal properties. In addition, we also studied the ability of these lignin fractions to form lignin nanoparticles and confirmed that fractions with trace amounts of carbohydrates were able to form uniform spherical lignin nanoparticles (LNPs) than those with large amounts of carbohydrates bonded fractions. In short, this study provided a profound understanding of the role of the carbohydrates bonded to lignin on the fractionation of lignin by organic solvents, further demonstrating how carbohydrates influence the characteristics of lignin.

Towards a deep understanding of the biomass fractionation in respect of lignin nanoparticles formation

“…80 mg of MF samples were dissolved in 0.7 mL of DMSO-d6 and placed into a 5 mm NMR tube, referenced at 39.5/2.5 ppm. The quantitative 31 P NMR analyzes were performed according to previous literature [32,39]. 20 mg of MF samples was dissolved in 300 µL of A solvent (anhydrous pyridine and deuterated chloroform (CDCl 3 ) 1.6:1, v/v), and 100 µL of dimethylformamide (DMF) under stirring.…”

“…Moreover, the utilization of LNPs into nanocomposites could open new possibilities for the development of novel materials with outstanding properties (e.g., toughening, UV shielding, antibacterial properties) [27,28]. There are many ways to prepare nanoparticles, and many studies are exploring the factors that affect the formation of nanoparticles, such as content of phenolic hydroxyl group [29,30], molar mass [31], the content of carbohydrates in lignin [32], etc. However, the well controllable preparation of LNPs is still a challenge including the shape and size of particles.…”

Lignin Nanoparticles for Enhancing Physicochemical and Antimicrobial Properties of Polybutylene Succinate/Thymol Composite Film for Active Packaging

“…Aside from the effects that modify the properties of materials, lignin is a natural antimicrobial agent because it contains numerous functional groups [ 21 ] that are responsible for antimicrobial activities [ 22 ], such as phenolic and aliphatic hydroxyls, methyl, carboxylic, and carbonyl groups. However, despite its great potential to replace synthetic chemicals, only 2–5% of lignin in its macromolecular form is commercially utilized [ 23 ].…”