Evaluation of sol-gel hybrid nanocomposites for dry medieval wood

Abstract

• Alum-treated wooden objects undergo chemical degradation, developing acidic pH. • Two hybrid nanocomposite systems were designed to preserve archaeological wood. • Hybrid systems can both consolidate and adjust the pH. • The MTES-based system appears the most promising treatment for archaeological wood. • Ca(OH) 2 NPs react with KHSO 4 turning into syngenite (K 2 Ca(SO 4 ) 2 · H 2 O). Viking Age archaeological wooden objects from the Oseberg find have undergone extensive chemical deterioration due to the original conservation treatment, based on alum salts (KAl(SO 4 ) 2 ·12H 2 O), done in the early 1900s. Today, the artefacts are highly acidic (pH ≤ 2), fragile and the wood has almost completely lost its structural integrity. This study is part of a wider research project on conservation methods for these finds, currently underway. Multi-functional organic/inorganic hybrid systems, engineered to deacidify and consolidate alum-treated wood in a single step, have been studied. These products, made of a polysiloxanes’ network and nanostructured Ca(OH) 2 , have given promising results in terms of penetration, deacidification, consolidation and maintenance of the wood properties. This work provides a comparison between two hybrid systems having in common a backbone of poly(dimethylsiloxane) hydroxy‑terminated (PDMS-OH) and alkaline nanoparticles (NPs) (as deacidifying agent), along with tetraethyl orthosilicate (TEOS), methyltriethoxysilane (MTES) applied to fresh and archaeological wood, respectively. Colour, pH, dimensions, SEM-EDS and ultrasonic velocity measurements, in addition to hardness tests, were collected on the treated mock-ups to investigate the outcomes of the two systems in terms of conservation efficacy. FTIR-ATR and DVS have also been carried out for systems characterization. From the analysis performed, the most promising hybrid system seems to be the one prepared with MTES as structural polymer. In addition, it has been highlighted the requirement of a method for sol application other than immersion when objects are already treated with resins.