Natural Deep Eutectic Solvents as Rust Removal Agents from Lithic and Cellulosic Substrates.

Area of Science:

• Materials Science
• Chemistry
• Conservation Science

Background:

• Deep eutectic solvents (DESs) possess unique physicochemical properties, including tunability, making them suitable for diverse applications.
• While DESs can dissolve metal oxides, their efficacy in removing rust from delicate substrates like textiles and stone has been underexplored.

Purpose of the Study:

• To evaluate the rust removal capabilities of three distinct DESs based on choline chloride and different organic acids (acetic, oxalic, citric).
• To assess the effectiveness of these DESs on cellulose-based materials (linen fabric) and lithotypes (travertine, granite) with artificial rust stains.

Main Methods:

• Three DES formulations were prepared using choline chloride with acetic, oxalic, or citric acid.
• DESs were applied to artificially rusted linen, travertine, and granite samples using cellulose poultices or cotton swabs.
• Cleaning effectiveness and potential side effects were analyzed using macro/microscopic observation, colorimetry, and SEM/EDS.

Main Results:

• The DES formulated with oxalic acid demonstrated successful rust stain removal from both linen fabric and stone samples.
• The choline chloride/citric acid DES effectively removed rust from stone but was less effective on linen.
• The choline chloride/acetic acid DES showed limited rust removal efficacy across tested substrates.

Conclusions:

• Oxalic acid-based DES presents a viable, novel method for eliminating rust stains from valuable cellulosic and lithic artifacts.
• DESs offer a promising avenue for the conservation and restoration of historical and artistic objects affected by corrosion.