Kumagawa and Soxhlet Solvent Fractionation of Lignin: The Impact on the Chemical Structure

Abstract

We investigated the effects of solvent fractionation on the chemical structures of two commercial technical lignins. We compared the effect of Soxhlet and Kumagawa extraction. The aim of this work was to compare the impact of the methods and of the solvents on lignin characteristics. Our investigation confirmed the potentialities of fractionation techniques in refining lignin properties and narrowing the molecular weight distribution. Furthermore, our study revealed that the Kumagawa process enhances the capacity of oxygenated solvents (ethanol and tetrahydrofuran) to extract lignin that contains oxidized groups and is characterized by higher average molecular weights. Furthermore, the use of tetrahydrofuran after ethanol treatment enabled the isolation of lignin with a higher ratio between carbonyl and other oxidized groups. This result was confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), 13 C NMR and two-dimensional (2D) NMR spectroscopies, gel permeation chromatography (GPC), and analytical pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) analysis. Ultraviolet–visible (UV–vis) spectra evidenced the enrichment in the most conjugated species observed in the extracted fractions. Elemental analyses pointed at the cleavage of C-heteroatom bonds enhanced by the Kumagawa extraction.

Nanocellulose for Paper and Textile Coating: The Importance of Surface Chemistry

“…Delignification is a process requiring the complete solubilization of lignin, which is usually removed and represents a waste of the pulping process. [61,62] Other approaches, like mechanical treatments using a refiner and a high-pressure homogenizer; microfluidization, high-intensity ultrasonication (HIU) or cryo-crushing, and swelling of cellulosic fibers with water, [63][64][65] are also used to scale down the cellulosic materials. Presently, these techniques are not efficient and cost-effective enough to be used in the paper and paperboard industries.…”

“…Furthermore, cellulose deriving from plants usually requires a careful purification from lignin and hemicelluloses prior to the mechanical, chemo‐mechanical, or mechanical‐enzymatic treatment. Delignification is a process requiring the complete solubilization of lignin, which is usually removed and represents a waste of the pulping process [61,62] …”

Kraft Lignin: From Pulping Waste to Bio‐Based Dielectric Polymer for Organic Field‐Effect Transistors

“…On the other side, parallel attempts of removing ashes by solvent fractionation were sided by an undesirable solvent chemical derivatization of L2 . [ 62 ] We proceeded to the completion of the final comparison, namely fabrication of OFET devices with the two lignins as stand‐alone dielectrics, and assessed both L1 and L2 lignin on plain aluminum gate electrodes, without the presence of alumina layer. We evaluated L1 and L2 lignin dielectric layers of various thicknesses, stemming from stock solution of various concentrations of the two lignins in 1:1 mixture of ethanol and ammonia.…”

“…For pentacene the molecular orientation is one of the requisites for inducing large aggregates. [ 62 ] However, it is well known that this semiconductor can yield polymorphic films upon evaporation. [ 63 ] This intricate behavior will probably require further studies to understand the limited aggregation capacity of pentacene on the two lignins, and the careful growth of pentacene monolayers will definitely shed more light into this aggregation mechanism.…”

Isolation of Pure Lignin and Highly Digestible Cellulose from Defatted and Steam-Exploded Cynara cardunculus

“…While biomass fractionation to isolate cellulose has been widely demonstrated, , isolation of useful forms of hemicellulose and lignin on an industrial scale is still under development. Nonetheless, due to the prominence of aromatic derivatives in strategic chemical sectors, several areas have explored the use of pure lignin. − However, lignin valorization is difficult to achieve due to the degradation occurring during the pretreatment step and the intrinsic insolubility of the native lignin. The lignin polymer is reactive under isolation conditions, and its native structure is difficult to preserve, as it is often necessary to alter it by functionalization or depolymerization to achieve complete dissolution. , The aqueous acid pretreatments could generate condensed lignin with C–C linkages and the cleavage of β-aryl ether units .…”