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Membrane filtration of kraft lignin: Structural charactristics and antioxidant activity of the low-molecular-weight fraction
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
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2018 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 112, p. 200-209Article in journal (Refereed) Published
Abstract [en]

Lignin, which is the second most abundant biomass component and has carbon-rich phenolic content, is a promising renewable raw material for multiple applications, such as carbon fibers, adhesives, and emulsifiers. To use lignin efficiently, it is important to ensure its purity and homogeneity. As a result, the separation of lignin into fractions with high purity and narrow molecular-weight distributions is likely a prerequisite for several applications. Ultrafiltration using ceramic membranes has many advantages, including enabling direct lignin extraction from Kraft pulp cooking liquors without pH and temperature adjustment. One challenge with membrane filtration using such a system is the potential for reduced membrane performance over time, which is associated with fouling. In this study, LignoBoost Kraft lignin was fractionated using a ceramic membrane with a molecular weight cut-off of 1 kDa. The separation behavior during ultrafiltration fractionation was investigated and the antioxidant properties of the recovered low-molecular-weight (low-MW) lignin samples were evaluated. Using this model system, the permeate fluxes were unstable during the 100 h of membrane operation. However, a decrease in the average MW in the permeate over time was observed. The shift in MW was most pronounced for virgin membranes, while a more stable MW distribution was evident for membranes subjected to multiple cleaning cycles. According to 2D NMR analysis, low-MW lignin that was recovered after 100 h of operation, consisted of smaller lignin fragments, such as dimers and oligomers, with a high content of methoxy-groups. This was confirmed using the size exclusion chromatography method, which indicated an weigh average molecular weight in the range of 450–500 Da. 31P NMR spectroscopy showed that, despite the lower total content of phenolic OH groups, the low-MW sample had a higher proportion of non-condensed phenolic OH groups. The results of the antioxidant tests demonstrated the strong potential of lignin and its low-MW fraction as a natural antioxidant, particularly for lipid-containing systems. The low-MW lignin fraction showed better antioxidant activity than the non-fractionated LignoBoost lignin in the kinetic oxygen radical absorbance capacity (ORAC) test and demonstrated three-fold stronger inhibition of the substrate (fluorescein) than the reference antioxidant Trolox (a water-soluble derivative of vitamin E).

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 112, p. 200-209
Keywords [en]
Antioxidant activity, LignoBoost lignin, Low-MW lignin, Structural analysis, Ultrafiltration
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-220194DOI: 10.1016/j.indcrop.2017.11.042ISI: 000425561900026Scopus ID: 2-s2.0-85036614166OAI: oai:DiVA.org:kth-220194DiVA, id: diva2:1167305
Note

QC 20171218

Available from: 2017-12-18 Created: 2017-12-18 Last updated: 2018-03-13Bibliographically approved

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Sevastyanova, Olena

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Aminzadeh, SeldaLindström, MikaelSevastyanova, Olena
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Fibre and Polymer TechnologyWallenberg Wood Science Center
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