Open access publications in the SLU publication database

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.