Extraction and Surfactant Properties of Glyoxylic Acid‐Functionalized Lignin

Abstract

The amphiphilic chemical structure of native lignin, composed by a hydrophobic aromatic core and hydrophilic hydroxy groups, makes it a promising alternative for the development of bio‐based surface‐active compounds. However, the severe conditions traditionally needed during biomass fractionation make lignin prone to condensation and cause it to lose hydrophilic hydroxy groups in favour of the formation of C−C bonds, ultimately decreasing lignin's abilities to lower surface tension of water/oil mixtures. Therefore, it is often necessary to further functionalize lignin in additional synthetic steps in order to obtain a surfactant with suitable properties. In this work, multifunctional aldehyde‐assisted fractionation with glyoxylic acid (GA) was used to prevent lignin condensation and simultaneously introduce a controlled amount of carboxylic acid on the lignin backbone for its further use as surfactant. After fully characterizing the extracted GA‐lignin, its surface activity was measured in several water/oil systems at different pH values. Then, the stability of water/mineral oil emulsions was evaluated at different pH and over a course of 30 days by traditional photography and microscopy imaging. Further, the use of GA‐lignin as a surfactant was investigated in the formulation of a cosmetic hand cream composed of industrially relevant ingredients. Contrary to industrial lignins such as Kraft lignin, GA‐lignin did not alter the color or smell of the formulation. Finally, the surface activity of GA‐lignin was compared with other lignin‐based and fossil‐based surfactants, showing that GA‐lignin presented similar or better surface‐active properties compared to some of the most commonly used surfactants. The overall results showed that GA‐lignin, a biopolymer that can be made exclusively from renewable carbon, can successfully be extracted in one step from lignocellulosic biomass. This lignin can be used as an effective surfactant without further modification, and as such is a promising candidate for the development of new bio‐based surface‐active products.

Dissolution and Hydrolysis of Wood Particles in Glyoxylic Acid without Ball Milling

“…We presume that the (hemi)­acetal or ester is formed with not only the hydroxy groups of cellulose but also those of lignin. When birch wood is reacted with glyoxylic acid in the presence of hydrochloric acid, HSQC-NMR analysis showed that the formation of stable acetals allows lignin extraction while preventing condensation and repolymerization reactions . Similarly, the reduced blackening of lignin in this study may be due to prevented condensation and repolymerization reactions.…”

“…Bubbles were observed in the wood solution, suggesting that the lignin-derived surface-active agent , can possibly induce foamability. The uniform dispersion of the wood in the liquid glyoxylic acid was challenging in the presence of air bubbles.…”

Controlled dual functionalization of lignin generates unique properties in gelatin-based hydrogels

“…S4.2). [15,16] We observed that the ratio of TALD/GA introduced in the reactor prior to extraction was linearly correlated with the TALD/GA ratio measured on the lignin after extraction (Figure 1d). We also noticed that the two aldehydes had a similar reactivity and that simply varying the aldehyde quantities introduced during AAF we could precisely and simultaneously control the type and degree of lignin functionalization. )…”

“…[13,14] We also showed that multifunctional aldehydes could be employed to simultaneously extract and functionalize lignin at high yields which could facilitate its use as a surfactant or for further functionalization for use in resins. [15,16] For multiple high-end material applications including soft tissue engineering, the targeted material must not only be biocompatible, but must also present well-defined rheological and other mechanical properties. Such properties are necessary to mimic the surrounding environment in which they are employed, and to ultimately trigger the desired biological responses.…”

Stepping away from purified solvents in reductive catalytic fractionation: a step forward towards a disruptive wood biorefinery process

“…[14][15][16] Recently, multiple novel biorefinery concepts have attempted to overcome this typical drawback of traditional, carbohydrate-centred biorefining e.g., by preventing lignin recondensation through either catalysis [17][18][19][20][21][22] or protection-group chemistry. [23][24][25] These technologies are generally referred to as lignin-first biorefining. 26,27 One such a promising lignin-first biorefinery concept is reductive catalytic fractionation (RCF).…”