| 1. |
- Almkvist, Gunnar, et al.
(author)
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Prediction of tensile strength in iron-contaminated archaeological wood by FT-IR spectroscopy - a study of degradation in recent oak and Vasa oak
- 2016
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In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 70:9, s. 855-865
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Journal article (peer-reviewed)abstract
- Oak from the Swedish warship Vasa and recent oak that was aged after impregnation with iron(II) chloride has been analyzed by FT-IR spectroscopy and submitted to tensile strength testing. The aim was to investigate correlations between FT-IR bands in the fingerprint region, chemical degradation, and tensile strength in iron contaminated oak. The concentration of carboxylic functions increased and the acetyl groups in the hemicellulose fraction were decreasing as a function of degradation time. These changes are accompanied by reduced tensile strength and elevated content of oxalic acid (OA) in both Vasa wood and the impregnated recent oak samples. To evaluate the possibility to predict tensile strength from spectral data, chemometric modeling by partial least-squares (PLS) regression was applied. The strategy of repeated double cross validation (rdCV) allowed a realistic prediction of tensile strength. Overall, chemical changes and mechanical performances of iron contaminated wood are strongly correlated and thus FT-IR spectroscopy is suited to predict the strength properties of the degraded wood.
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| 2. |
- Norbakhsh, Shahin
(author)
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Deterioration of recent oak by iron compound : a comparison with Vasa oak
- 2012
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Licentiate thesis (other academic/artistic)abstract
- Wood degradation in the historical warship Vasa has been studied systematically regarding the chemical and physical properties. The presence of iron(II) seems to be one important factor for the degradation of the wood, causing reduction of its tensile strength. This is unfortunately a serious problem as iron(II) compounds are abundant in Vasa wood. However, it is a question whether the deterioration reactions still go on or if they have stopped soon after the ship was salvaged. The aim of this study is to investigate the possible chemical reasons for the deterioration of the wood. This has been accomplished by use of model experiments with recent oak. Series of recent oak wood, cut in a “dog bone shape”, were placed in aqueous solutions containing 0.1 M iron(II) chloride. These samples were exposed to different concentrations of oxygen for one week, one month and one year. By use of an Instron universal testing machine the samples were pulled apart and the tensile strength required to break the wood registered. Samples exposed to iron(II) and oxygen showed a significant decrease in tensile strength. Variation of time and oxygen exposure showed that the rate of decrease in tensile strength is more intense at the initial stages of the exposure. The results also showed that exposure to pure oxygen, increased the deterioration rate. Oxygen treated samples showed an increase in the formation of low-molecular organic acids in the wood tissue and pH decreased to approximately 2 to 3. The chemical properties of holocellulose in recent oak treated with aqueous iron(II) solutions in the presence of oxygen conforms very well with degraded wood from the Vasa. The deterioration process in the Vasa wood seems to be limited in time and probably took place soon after oxygen exposure. The abundance of iron(II) compounds in Vasa wood and accessibility of oxygen and water will determine the level of deterioration of the wood.
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| 3. |
- Norbakhsh, Shahin, et al.
(author)
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Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood
- 2014
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In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:6, s. 649-655
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Journal article (peer-reviewed)abstract
- In the wood of the Swedish 17th century warship Vasa, iron (Fe)-catalyzed chemical degradation has taken place after the salvation in 1961, which is manifested in increased acidity accompanied by cellulose degradation and reduced strength in the oak hull. Model studies on fresh oak impregnated with Fe(II) also led to tensile strength (TS) reduction in the same order of magnitude as observed in the wood of the Vasa. In the present study, further experiments have been performed concerning the Fe-catalyzed wood degradation. Namely, the degree of wood degradation was monitored quantitatively by measurement of the O-2 consumption of Fe(II)-impregnated oak, kept in closed vials with different relative humidities (RH), as a function of time. The initial O-2 consumption was high and declined with time. After 200 days, the accumulated O-2 consumption was 0.3-0.4 mmol g(-1) wood. Degradation products with low molecular weight were analyzed. The release of CO2 and oxalic acid (OA) was positively correlated with RH (0.235 and 0.044 mmol g(-1), respectively, at RH98% after 200 days). Samples kept for 1500 days at RH54% had accumulated 0.044 mmol OA g(-1) wood, which is equal to the average OA content in the interior of Vasa oak (corresponding to 4 mg g(-1)). Oak samples, from which extractives had been removed prior to Fe(II) impregnation, did not change their O-2 consumption or TS reduction compared to the nonextracted samples, indicating that extractives are not essential for cellulose degradation in this context.
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| 4. |
- Norbakhsh, Shahin
(author)
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Implication of chemical deterioration on mechanical performance of wood
- 2014
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Doctoral thesis (other academic/artistic)abstract
- The oak wood of the 17th century warship Vasa has shown significant changes in the chemical and mechanical properties as compared to recent oak. The most important factors contributing to these changes are the incorporation of iron compounds during waterlogging and the uptake of polyethylene glycol (PEG) in the course of the preservation treatment. To investigate the effect of iron-dependent oxidative degradation reactions, samples of recent birch, pine and oak were impregnated with aqueous iron(II) chloride solution and thereafter exposed to air or pure oxygen at controlled relative humidity in long-term experiments, followed by tensile strength (TS) measurements. Iron-impregnated samples exposed to oxygen displayed significant effects already after one week and with a reduction in TS of ~50% after one year. Samples treated with additional PEG displayed less reduction in TS. The extent of oxidative degradation was monitored quantitatively following the O₂ consumption in closed vials with different relative humidity (RH), as a function of time. For oak, the initial O₂ consumption was high and declined with time. After 200 d, the accumulated O₂ consumption was 0.3-0.4 mmol∙(g wood)-1. The formation of carbon dioxide and oxalic acid was positively correlated with RH. Samples kept for 1500 d at RH55% had accumulated 0.044 mmol oxalic acid∙(g wood)-1, which equals the average oxalic acid content in the interior of Vasa oak. FT-IR analysis on iron(II) impregnated samples and on Vasa wood showed an increased signal intensity at 1710 cm-1, assigned to carbonyl functions, in samples with reduced TS. The signal at 1710 cm-1 is not primarily related to oxalic acid. The results show that chemical changes and mechanical performance of iron contaminated wood are strongly correlated and that the state of degradation is observable using IR spectroscopy. Overall, the results confirm that iron compounds have a detrimental effect in wood and indicate that PEG might act as an antioxidant in oxidative degradation processes. Concerning the Vasa, it may be concluded that most degradation related to iron compounds and oxidative processes has taken place during the first period of conservation when the wood was exposed to oxygen in a still very humid state. Thus, the current rate of oxidative degradation under the present relatively dry museum conditions should be relatively low.
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| 5. |
- Norbakhsh, Shahin, et al.
(author)
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Mimicking of the strength loss in the Vasa : model experiments with iron-impregnated recent oak
- 2013
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In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:6, s. 707-714
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Journal article (peer-reviewed)abstract
- Previous studies of the oak wood of the 17th century warship the Vasa have shown significant changes in the chemical and mechanical properties compared with recent oak. The most important factors contributing to these changes are the incorporation of iron compounds during waterlogging and the uptake of polyethylene glycol (PEG) in the course of the 17 years of preservation treatment. To investigate the effect of iron-dependent oxidative degradation reactions, recent oak wood samples were impregnated with aqueous iron(II) chloride solution (0.1 M) and thereafter exposed to air or pure oxygen at controlled relative humidity in long-term experiments followed by tensile strength (TS) measurements. The iron-impregnated samples exposed to oxygen displayed significant effects already after 1 week and the reduction in TS was similar to 50% after 1 year. The samples treated with additional PEG displayed less TS reduction, whereas the addition of cysteine had no effect. The size exclusion chromatography of treated samples showed that the average molecular weight of holocellulose had decreased. The results confirm that iron compounds have a detrimental effect in wood and indicate that PEG might act as an antioxidant for the degradation processes. Concerning the Vasa, it may be concluded that most degradation related to iron compounds and oxidative processes have taken place during the first period of conservation when the wood was exposed to oxygen in a still very humid state. Thus, the current rate of oxidative degradation under the present relatively dry museum conditions should be relatively low.
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