刊行物

刊行物
(Lignin)
Vol.1(2020)
Original article
Utilization of Recyclable MnO2 in Prebleaching Stage as a Catalyst for Oxygen Delignification or as a Delignifying Agent

Shirong Sun, Takuya Akiyama, Tomoya Yokoyama, Yuji Matsumoto
Pages: 1-10
Published online: 28 May 2020

Abstract: MnO2 can potentially suppress the degradation of carbohydrates in oxygen delignification, because MnO2 catalyzes the decomposition of H2O2 to H2O and O2 and possibly that of organic peroxides to alcohols and O2 without the formation of any active oxygen species, which degrade carbohydrates. The addition of MnO2 actually suppressed the degradation of a carbohydrate model compound, methyl β-D-glucopyranoside, when reacted with active oxygen species generated from reactions between a phenolic lignin model compound, vanillyl alcohol, and O2 under oxygen delignification conditions. However, the addition of MnO2 did not have any meaningful effect when hardwood unbleached kraft pulp was oxygen-delignified. The addition surprisingly had a deleterious effect on pulp viscosity when MnO2 was generated in situ in pulp fibers. This deleterious effect would result from a phenomenon whereby the oxidation of Mn2+ to MnO2 was not complete in the in situ generation and Mn3+ -related species, along others, were generated. In contrast, substitution of the latter half of oxygen delignification with a MnO2 oxidation stage at a pH of 2 substantially suppressed the degradation of carbohydrates, compared to the common oxygen delignification without substitution.
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Original article
Potential of Lignin as Antioxidant for Thermoplastics and Other Materials

Petri Widsten, Tiina Liitiä, Kirsi Immonen, Marc Borrega, Anna-Stiina Jääskeläinen, Hanne Wikberg, Taina Ohra-aho, Tarja Tamminen
Pages: 11-19
Published online: 28 May 2020
Abstract: The antioxidant properties of technical lignins have been extensively investigated but there are still gaps of knowledge that should be filled to facilitate the practical applications of lignins as antioxidants (AOs). In the present investigation, we compared the short-term (60 min) and long-term (48h) AO performance of lignins with different contents of functional groups and lignin model compounds (LMCs) with different aromatic ring substituents in the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH*) antioxidant assay. We found some LMCs to quickly expend their AO capacity while others started off slowly but after 48h had consumed more DPPH* per phenolic hydroxyl group. Reaction time was also a factor in the relative AO performance of lignins. For softwood lignins, a higher phenolic hydroxyl content was associated with increased DPPH* reactivity. CatLignin, a thermally treated lignin rich in phenolic units and especially catechol groups, consumed more than twice as much DPPH* than any other lignin during 48h (over two mol/lignin unit of 180 g/mol). CatLignin also had the lowest 60 min half-maximal effective concentration (EC50). In polypropylene, lignins provided better UV protection than commercial primary antioxidants applied at similar loadings. Similarly, the better performance of lignin over commercial AOs was observed against thermal oxidation.
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Original article
Comparison of Dehydrogenation Polymers by Commercial Enzymes, Laccase from Rhus vernicifera and Horseradish Peroxidase

Tatsuya Matsumoto, Keiichi Koda, Kengo Shigetomi, Manish Kumar, Yasumitsu Uraki
Pages: 20-28
Published online: 28 May 2020
Abstract: Dehydrogenation polymers (DHPs) were prepared by laccase from Rhus vernicifera and horseradish peroxidase (HRP). The enzymatic ability of oxidation and polymerization was compared between these enzymes. Laccase showed higher enzyme activity against syringaldazine than ABTS, while HRP exhibited lower enzyme activity against syringaldazine than 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). These enzymes had various enzyme activity against these substrates. DHPs from sinapyl alcohol (SA) were hardly produced by each enzyme, whereas DHPs from coniferyl alcohol (CA) were produced by both enzymes. The laccase oxidized sinapyl alcohol faster than coniferyl alcohol. The nuclear magnetic resonance (NMR) analysis demonstrated that acetylated-DHP (Ac-DHP) from CA by laccase contained β-5 and β-β linkages, but not β-O-4 linkage. On the other hand, Ac-DHP from CA by HRP carried all these three linkages.
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