This study aimed to resolve the issue of the lack of detailed understanding of the effect of initial lignin content in hardwood kraft pulps on pulp delignification by deep eutectic solvents. The authors used Kappa number of the concerned pulp, intrinsic viscosity, and selectivity and efficiency of delignification as the parameters of the effect. The pulp (50 g oven dry pulp) was treated with four different DESs systems based on choline chloride with lactic acid (1:9), oxalic acid (1:1), malic acid (1:1), and system alanine:lactic acid (1:9); the results were compared to those reached by oxygen delignification. The results showed that the pulp with a higher initial lignin content had a greater fraction of easily removed lignin fragments.

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In this short communication, UV/Vis spectrophotometry is described as an analytical tool for the quantification of lignin content in deep eutectic solutions. The lignin was solubilized with different deep eutectic solvent (DES). DESs were prepared as binary mixtures of choline chloride with lactic acid (1:9); (1:10); ethylene glycol (1:2); glycerol (1:2) and alanine:lactic acid (1:9), and betaine:lactic acid (1:2). The UV-Vis spectrometric quantification of the solubilized lignins was independent of the type of solubilized lignin. The approach consists of measuring the absorbance of a solution of lignins dissolved in the deep eutectic solvents at an absorbance of 440 nm.

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