Ultraviolet Spectrophotometry of Lignin Revisited: Exploring Solvents with Low Harmfulness, Lignin Purity, Hansen Solubility Parameter, and Determination of Phenolic Hydroxyl Groups

Abstract

In this article, we explored solvents with lower harmfulness than established systems for UV spectrophotometry of lignin. By measuring the absorptivity in DMSO solvent at 280 nm, the purity of the lignin samples was addressed and compared with Klason and acid-soluble lignin. The general trend was an increasing absorptivity with increasing lignin purity; however, considerable scattering was observed around the sample mean. The Hansen solubility parameter (HSP) of four technical lignins was furthermore determined. The model was in line with the UV measurements, as solvents closer in HSP correlated with a higher absorptivity. Ethylene glycol was identified as a good solvent for lignin with low UV-cutoff. In addition, mixtures of propylene carbonate, water, and ethanol showed good suitability and a low cutoff of 215 nm. While DMSO itself was poorly suited for recording alkali spectra, blending DMSO with water showed great potential. Comparing three methods for determining phenolic hydroxyl units by UV spectrophotometry showed some discrepancies between different procedures and solvents. It appeared that the calibrations established with lignin model compounds may not be fully representative of the lignin macromolecule. More importantly, the ionization difference spectra were highly affected by the solvent of choice, even when using what are considered "good" solvents. At last, a statistical comparison was made to identify the most suitable solvent and method, and the solvent systems were critically discussed. We thus conclude that several solvents were identified, which are less harmful than established systems, and that the solubility of lignin in these is a crucial point to address when conducting UV spectrophotometry.

Interfacial Adsorption of Oil-Soluble Kraft Lignin and Stabilization of Water-in-Oil Emulsions

“…A platinum Du Noüy Ring was used. Each sample was prepared immediately before the interfacial measurement, as previous results have indicated that aging may affect the sample . The modified lignin was weighed into a volumetric flask and topped up with petroleum distillate, and the mixtures were stirred until complete dissolution.…”

“…Solubility of lignin in organic solvents is important to process, modify, and utilize this biopolymer. , Technical lignin, such as Kraft, soda, and organosolv lignin, is reportedly soluble in some aprotic polar solvents, such as dimethyl sulfoxide and dimethylformamide, and some protic polar solvents, such as ethylene glycol, ethylene glycol monoethyl ether (“Cellosolve”), 1-methoxy-2-propanol (“Dowanol”), and diethylene glycol monobutyl ether (“Butyl Carbitol”). , Both the extraction process and the biomass origin can have minor effects on the solubility of these lignin types. Lignosulfonates, on the other hand, are highly hydrophilic and are hence reported to be soluble in water, propylene glycol, ethylene glycol, and dimethyl sulfoxide .…”

Solubility and Thermodynamic Modeling of 5-Nitrofurazone in Pure Solvents and Binary Solvent Mixtures

“…The absorbance of the aqueous solution of 5-nitrofurazone was recorded at 375 nm. The average molar solubility of 5-nitrofurazone was calculated from the average absorbance values of eqs 1and . − where a is the absorbance value of the dilution solvent, V is the volume of the diluent, W is the dilution factor, and k and b are the slope and intercept of the calibration curve, respectively. m 1 and m i ( I ⩾ 2) represent the mass of 5-nitrofurazone and solvent, respectively.…”

Valorization of lignin for advanced material applications: a review

“…40 The solubility of lignin macromolecules in appropriate solvents is a critical parameter for effective modication reactions. 42,43 Conventional solvents for lignin include dimethyl sulfoxide (DMSO), toluene, acetone, ethanol, pyridine, methanol, dimethyl formamide (DMF), tetrahydrofuran (THF), chloroform, and dichloromethane. [43][44][45][46] Also, lignin moieties are known to be soluble in hot alkaline solutions.…”

“…42,43 Conventional solvents for lignin include dimethyl sulfoxide (DMSO), toluene, acetone, ethanol, pyridine, methanol, dimethyl formamide (DMF), tetrahydrofuran (THF), chloroform, and dichloromethane. [43][44][45][46] Also, lignin moieties are known to be soluble in hot alkaline solutions. 44,46,47 Additionally, the solubility of lignin could be further improved by fractionation.…”