Study of an eco-friendly path to prepare effective alkoxysilane-based consolidants for stone conservation without organic solvents

• New mixtures with Dyn 40 oligomeric precursor and acid/base catalysts were designed. • Catalyst and water ratios play an important role in the preparation of adequate mixtures. • Both types of catalysts are capable to generate formulations with suitable characteristics. • Designed mixtures were capable to improve the drilling resistance of stones. • Effective stone consolidants were developed without the addition of solvents. Finding a balance between technical performance and eco-friendliness in consolidants for stone conservation has proven to be challenging. This work explores the development of eco-friendly, organic solvent-free alkoxysilane consolidants for stone conservation. To eliminate the use of organic solvents, acid-catalysed pathways were investigated and compared with base-catalysed ones. Reaction parameters such as catalyst concentration, water content, and sonication time were varied to determine the optimal composition of the product mixtures. Ultimately, mixtures with adequate penetration capability for porous stones, enabling effective in-depth consolidation, were successfully prepared. Additionally, these mixtures exhibited a reduced tendency for surface accumulation, minimizing potential adverse effects. Among the concentrations investigated, the acid-catalysed mixtures demonstrated favorable gelling times and more suitable morphological and structural characteristics compared to those prepared under basic conditions. These improvements were attributed to the more thorough hydrolysis and condensation reactions achieved in acidic media. The results confirmed that the addition of organic solvents is unnecessary, paving the way for a new generation of organic solvent-free alkoxysilanes for conservation purposes.