Case Study in Kraft Lignin Fractionation: “Structurally Purified” Lignin Fractions—The Role of Solvent H-Bonding Affinity

Self Cite

An analytical approach based on phenol fluorescence labeling with the dansyl fluorophore coupled with gel permeation chromatography using UV and fluorescence detection was applied in an effort to increase the understanding of the phenolic group distribution in different lignin specimens. Selective derivatization with dansyl chloride of lignin phenolic functionalities was quantitatively achieved under mild reaction conditions and was applied to acidolytic and kraft lignins from softwood and hardwood and to kraft lignin fractions obtained by solvent fractionation. Acetylated lignins and labeled lignins were analyzed to discern the lignin aromatic skeleton input from the response of dansyl-linked phenols, successively, allowing for estimation of the phenolic group distribution as a function of molecular weight for different lignins before and after solvent fractionation.

Section: Structural Interpretation Of Phenol Distributions In Molecul...mentioning

confidence: 99%

Phenolic Group Distribution as a Function of Molecular Weight in Lignins and Their Fractions

Salanti

Orlandi

Lange

et al. 2022

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“…Consequently, lignin fractions with declining M w were sequentially precipitated upon the amount of hexane addition in this work. Compared with the successive precipitation method using acetone followed by methanol, F ins in this work precipitated from the lignin dissolved by the acetone–methanol cosolvent had a higher M w (11,188 vs 9,430 Da), suggesting that the acetone–methanol cosolvent can dissolve more high- M w lignin than a single solvent. The F ins had a wider Đ M than KL, which may be due to the presence of carbohydrates and/or lignin–carbohydrate complex of which the M w is much different from that of lignin. , On the contrary, the Đ M of the other three fractions, F1, F2, and F3, are in the range from 2 to 3 smaller than that of KL (Table ) and are comparable with the previously reported Đ M of 1.4–2.2 and 1.5–2.5, suggesting that the acetone–methanol cosolvent fractionation method used in this work effectively refines KL into more uniform fractions.…”

Section: Resultsmentioning

confidence: 79%

Effect of the Lignin Structure on the Physicochemical Properties of Lignin-Grafted-Poly(ε-caprolactone) and Its Application for Water/Oil Separation

Xie

Meng

et al. 2022

Lignin-grafted poly(ε-caprolactone) copolymers (lignin-g-PCLs) have shown wide application potentials in coatings, biocomposites, and biomedical fields. However, the structural heterogeneity of lignin affecting the structures and properties of lignin-g-PCL has been scarcely investigated. Herein, kraft lignin is fractionated into four precursors, namely, Fins, F1, F2, and F3, with declining molecular weights and increased hydroxyl contents. Lignin-g-PCLs are synthesized via ring-opening polymerization of ε-caprolactone with lignin and characterized by GPC, FTIR, 1H and 31P NMR, DSC, TGA, and iGC. The mechanical properties, UV barrier, and enzymatic biodegradability of the lignin-g-PCLs are evaluated. Results show that lignin with a higher molecular weight and aliphatic OH favors the copolymerization, leading to lignin-g-PCLs with longer PCL arms. Moreover, lignin incorporation improves the thermal stability, hydrophobicity, and UV-blocking ability but reduces the lipase hydrolyzability of the copolymers. We also demonstrated that the lignin-g-PCL-coated filter paper could successfully separate chloroform–, petroleum ether–, and hexane–water mixtures with an efficiency up to 99.2%. The separation efficiency remains above 90% even after 15 cycles. The structural differences of copolymers derived from the fractionation showed minimal influence on the separation efficiency. This work provides new insights into lignin-based copolymerization and the versatility of lignin valorization.

“…Based on the above effect of entanglement and aggregation, lignin with high molecular weight, high content of flexible linkages, aliphatic hydroxyl and carboxyl groups, and high S/G ratio was absorbed by Lig-gel in alkaline and then held in an acid environment. In addition to the ratio of S/G/H units and functional groups, the affinity among lignin molecules could also be affected by many factors, molecular configuration and solvent effect, − which require further studies.…”

Section: Resultsmentioning

confidence: 99%

pH-Responsive Lignin Hydrogel for Lignin Fractionation

Li³

et al. 2021

The efficient strategy for lignin fractionation is of great significance for its valorization into aromatics, fine chemicals, and functional materials. In this work, inspired by the traditional gel filtration and pH-responding solubility of lignin, a pH-responsive lignin-based hydrogel was fabricated via a simple cross-linking reaction and used for specific fractionation of lignin. The fraction with a higher molecular weight, more flexible linkages, aliphatic hydroxyl and carboxyl groups, and a high S/G ratio tends to entangle or aggregate with the network of the hydrogel. The pore size and water absorbency of the hydrogel can be tuned in different pH environments. As the solution switches to an acid environment, the unabsorbed fraction was precipitated completely, while the absorbed fraction was held by the shrunken pores of the hydrogel and then released to the fresh alkaline solution. This new strategy will find a new green and smart pathway for the development of not only the pH-responsive hydrogel but also lignin valorization.