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Cellulose degradation in the Vasa: The role of acids and rust
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
2013 (English)In: Studies in Conservation, ISSN 0039-3630, E-ISSN 2047-0584, Vol. 58, no 4, 308-313 p.Article in journal (Refereed) Published
Abstract [en]

The oak timbers of the Swedish warship Vasa are deteriorating. High amounts of oxalic acid have been found along with a low pH and low molecular weight cellulose deep in the wood timbers. The iron-rich surface wood differs from the interior wood in that it displays higher pH and cellulose with higher molecular weight. The objective of this study was to determine why there is a difference in cellulose degradation, pH, and oxalic acid amount between the surface region and the interior of the Vasa timbers. Analysis of cellulose weight average molecular weight by size exclusion chromatography was performed, as well as quantification of oxalic acid and iron by high-performance anion exchange chromatography and atomic emission spectroscopy, respectively. It was found that a decrease in iron content coincides with an increase in oxalic acid concentration and a drop in pH at a certain depth from the wood surface. When iron-rich surface wood samples from the Vasa were mixed with an aqueous solution of oxalic acid, a fast increase of pH over time was observed. Neither interior wood poor in iron nor the fresh oak reference showed the same neutralizing effect during the time of measurement. This indicates that the presence of iron (rust) causes a neutralization of the wood, through the formation of iron(III) oxalato complexes, thus protecting the wood from oxalic acid hydrolysis. This effect was not observed to the same extent for other acids observed in Vasa wood (sulfuric, formic, glycolic, and acetic acids).

Place, publisher, year, edition, pages
2013. Vol. 58, no 4, 308-313 p.
Keyword [en]
Acid hydrolysis, Cellulose, Degradation, Iron, Neutralization, Oak wood, Oxalic acid, Vasa, Waterlogged wood
National Category
Polymer Technologies Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-121178DOI: 10.1179/2047058412Y.0000000069ISI: 000325138600004Scopus ID: 2-s2.0-84889677835OAI: oai:DiVA.org:kth-121178DiVA: diva2:617176
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research FormasVinnova
Note

QC 20130422

Available from: 2013-04-22 Created: 2013-04-22 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The warship Vasa: A Study of Lignin, Extractives and Acids in the oak wood
Open this publication in new window or tab >>The warship Vasa: A Study of Lignin, Extractives and Acids in the oak wood
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The oak wood timbers of the 17th century Swedish warship Vasa are weak. The weakening has been attributed to cellulose degradation, which is more extensive in the interior of the timbers compared to the surface regions. Further, the mechanism of cellulose degradation was attributed to oxidative reactions involving iron as a catalyst. In this work, the non-cellulosic wood components (lignin and extractives) in the wood of the Vasa have been studied in order to assess the level of degradation possibly caused by oxidative reactions. Because the interior of the wood timbers is more acidic and its cellulose more depolymerized than at the near surface regions, a general study of organic acidand iron concentrations with respect to different depths from the surface was also performed.

Characterization of lignin in the wood of the Vasa was done by means of wet chemical degradation (thioacidolysis) and subsequent GC-MS analysis of the degradation products, as well as CP/MAS 13C NMR spectroscopy of the wood. Dry acetone- and water extracts of the wood were analyzed by 13C NMR spectroscopy and MALDI-TOF mass spectroscopy in order to study the presence of gallo- and ellagitannins. No severe lignin degradation and no discernible amounts of hydrolysable tannins in the oak wood of the Vasa were detected, indicating that oxidative reactions are not the primary route to cellulose depolymerization.

High amounts of oxalic acid (analyzed by HPIEC) and a low pH have been found in the interior of the wood timbers, supporting acid hydrolysis as the main mechanism of cellulose depolymerization. Analysis of the iron distribution using ICP AES shows that iron is most abundant in the surface of the timbers and decreases as the concentration of oxalic acid increases. Experimental work also shows that some iron species (rust) in the Vasa neutralize oxalic acid, thereby protecting the surface wood from acid hydrolysis.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 33 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:19
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-121176 (URN)978-91-7501-678-8 (ISBN)
Presentation
2013-05-06, Rånbyrummet, Teknikringen 56, KTH, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20130422

Available from: 2013-04-22 Created: 2013-04-22 Last updated: 2013-04-22Bibliographically approved

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