Effects of iron removal treatments on the chemical and viscoelastic properties of waterlogged wood

The process of extracting iron from waterlogged wood was simulated on non-degraded oak wood (Quercus spp.) with the aim of evaluating the effect of three levels of pH (acid / close to neutral / alkaline, obtained using three products normally used to extract iron) on both the composition and the viscoelastic mechanical properties of wood samples. The three products were disodium-ethylenediaminetetraacetic acid (EDTA-2Na), tetrasodium-EDTA (EDTA-4Na), and citric acid, and they were used at different concentrations and different extraction durations. Environmental Scanning Electron microscopy (ESEM) was used to observe the microstructure before and after extraction, ATR-FTIR was used to analyse the chemical composition and Dynamical Mechanical Analysis (DMA) was used to assess the storage and loss moduli and the loss factor of samples after treatment. Mass loss measurements after treatments were also carried out. The results indicated that chelating agents inducing alkaline conditions could have an impact on both chemical and viscoelastic characteristics of wood, whereas neutral or acidic conditions did not appreciably affect the considered characteristics. The observed effects are related to modifications of hemicelluloses composition (with partial mass loss of wood), which provoked a clear increase of the viscous behaviour of the treated material. These modifications were only limitedly and indirectly detectable using the other considered techniques. Being induced by the obtained alkaline conditions, present results are generalizable to the various treatments where high pH is adopted, and hence not only limited to the iron removal process. Thus, based on the knowledge attained in this research, conservators can be aware of the potential impact of these treatments on the wood structure, and this should help in gaining greater control over this process.