Structural Analysis of Fast-Growing Aspen Alkaline Peroxide Mechanical Pulp Lignin: A Post-Enzymatic Treatment

Abstract

An enzymatic mild acidic hydrolysis was used to separate and purify residual lignin from alkaline peroxide mechanical pulp (APMP). Using the optimum conditions for the laccase treatment (pH 4.5, temperature 50 °C, lignin consistency of 1%, a reaction time of 60 min, and a laccase dosage of 8 μ/g), oven-dried lignin was treated with laccase and in a laccase mediator system (LMS) to explore the mechanism for laccase and the LMS modification of APMP. The changes of functional groups in lignin were analyzed using nuclear magnetic resonance ( C-NMR spectra revealed that the lignin structure changed significantly with the laccase and the LMS treatments. Meanwhile, GPC demonstrated that laccase without a mediator could lead to the polymerization of lignin, while the LMS could degrade the lignin. Hence, it was concluded that laccase is an attractive enzyme for lignin modification.

Influence of Oxygen and Mediators on Laccase-Catalyzed Polymerization of Lignosulfonate

“…As described by Wang et al in 2016, the oxidation of lignin with LMS can lead to a degradation of the lignin by the fact that Cβ of the β-O-4 functional groups decreased. 11,37 Additionally, a study by Potthast et al in 1999 demonstrated the fact that LMS polymerizes phenolic substrates. Depending on the time of the polymerization process, LMS can also degrade the formed polymers which was shown by a time-dependent measurement.…”

Understanding the structural changes of lignin in poplar following steam explosion pretreatment

“…L P and L S were isolated and refined by the enzymatic-mild acidic hydrolysis method (Jääskeläinen et al 2003;Guerra et al 2006). This isolation process could give the isolated lignin the characteristics of higher yield, higher purity and minor structural changes (Guerra et al 2006;Wang et al 2016). Lignin was isolated according to the procedure shown in Figure 1.…”

“…Interestingly, the total amounts of sidechain substructures in lignin structure dramatically decreased after steam explosion pretreatment, particularly in L L which had dissolved in the steam-exploded liquid during the steam explosion process. It is noteworthy that there were substituents on C α in the β-O-4′, β-β′, β-5′ and β-1′ linkages, so the main reason for decreases in these four structures could be explained by the destructive effect of the C α cationization on the binding bond (Wang et al 2016). In addition, lignin is a polymer sensitive to high temperature and acidic environment, and under these conditions, depolymerization and repolymerization occur, as shown in Figure 6 (Li et al 2007).…”