Nanotechnology for Vasa Wood De-Acidification

The conservation of the seventeenth-century Swedish warship Vasa is a challenge due the unique history of its recovery and the delicate interventions made for its preservation. In the past years the strong acidity of wood came out as a threat for its conservation. The large amount of sulfur, produced by metabolic action of bacteria in the seabed, partly converted to sulfuric acid, catalyzes the chemical degradation of the wood through the acid hydrolysis of cellulose. This contribution reviews recent studies on the degradation of Vasa wood. We show how wood acidity can be neutralized by the application of calcium or magnesium hydroxide nanoparticles, forming an alkaline reservoir inside the wood that protect it from further acid attack. This has been evidenced by the thermal analysis carried out on fresh wood, Vasa wood, artificially degraded wood, and paper samples studied as reference cellulose-made materials. Pyrolysis temperature of cellulose was studied, as an important parameter of degradation, also related to the acidity of wood. Decreases in the pyrolysis temperature of degraded cellulose were correlated to decreases of its polymerization degree. Thermal analysis has been also used to investigate the wood de-acidification efficacy after the treatment with alkaline nanoparticles. Hydro-thermally aging, carried out on de-acidified Vasa wood samples demonstrated that de-acidification with nanoparticles facilitates protection of wood toward further acid degradation.