Study of the oxygen effect on mechanical pulp lignin using an improved lignin isolation method

Abstract

Lignins from kraft and mechanical pulps were isolated before and after oxygen treatment with conventional methods (acidolysis and enzymatic isolation) and with a novel two-step method combining an enzymatic treatment and acidolysis. Results showed that the combined enzymatic hydrolysis-acidolysis made it possible to extract lignin from pulp with a better yield than acidolysis alone and with a higher degree of purity than after enzymatic hydrolysis alone. The lignin samples isolated with the two-step method were analysed by 13 C NMR, 19 F NMR and by gel permeation chromatography. It was shown that the behaviour of mechanical pulp lignin during oxygen treatment was different from that of kraft pulp lignin. Most of these differences could be explained by the lower phenolic content and larger molecular size of the mechanical pulp lignin. As a consequence, oxygen had a poor delignifying effect. Finally, 19 F NMR spectroscopy showed that oxygen could destroy some quinones induced by the alkaline conditions of the O stage.

Understanding the Degree of Condensation of Phenolic and Etherified C-9 Units of in Situ Lignins

“…One approach is to first isolate the lignin from the wood and then analyze it by a technique such as NMR spectroscopy. Lignin is most commonly isolated from wood by ball-milling followed by extraction of the solubilized lignin with a solvent, commonly a dioxane–water mixture, and a subsequent purification step. , The yields of lignin may be increased by combining this treatment with enzymes to degrade the carbohydrates or including a mild acid treatment in the process. , The proportion of condensed units in the resulting isolated lignin can be determined by 1 H NMR spectroscopy from the number of aromatic protons per aromatic ring or by quantitative 13 C NMR spectroscopy from the number of protonated carbons per aromatic ring. , In addition, specific interunit linkages can be quantified by NMR spectroscopy . The major limitation of this approach is that the isolated lignins such as milled wood lignins (MWLs) are not necessarily representative of the native lignin, because they represent only a small proportion of the lignin in the original wood, and lignins may be structurally modified during their isolation…”

“…9,10 The yields of lignin may be increased by combining this treatment with enzymes to degrade the carbohydrates 11 or including a mild acid treatment in the process. 12,13 The proportion of condensed units in the resulting isolated lignin can be determined by 1 H NMR spectroscopy from the number of aromatic protons per aromatic ring 14 or by quantitative 13 C NMR spectroscopy from the number of protonated carbons per aromatic ring. 15,16 In addition, specific interunit linkages can be quantified by NMR spectroscopy.…”

Pulp delignification with oxygen and copper(II)-polyimine complexes

“…In this context, a fully bleached pulp (containing carbohydrates only) was mixed with a mechanical pulp (TMP, containing native lignin). This substrate contains etherified lignin, which is resistant to conventional oxygen delignification (Marlin et al 2005), but its lignin content was similar to that in an industrial UKP. The expectation was that the nonphenolic lignin in the model mixture with high molecular weight would be a good substrate to assess oxygen activation.…”

“…(Kn) of 20.6. It contained 3.2% native lignin (measured according to the Klason method), supposed to be resistant to conventional oxygen delignification (Marlin et al 2005). Pulp 2: BSKP (provided by Fibre Excellence) with initial Tappi viscosity of 10.4 mPa s. This pulp is virtually free of lignin.…”

“…This model pulp contains only a highly polymerized and nonphenolic lignin with abundant β-O-4 linkages between the phenyl propane units (Gellerstedt et al 1984). Contrary to phenolic kraft lignin, the etherified native lignin is not reactive during the O-delignification (Marlin et al 2005). The effects of catalysts were controlled based on the variations of Kn, which were only small but which may be nevertheless indicative.…”