PVA-based peelable films loaded with tetraethylenepentamine for the removal of corrosion products from bronze

Abstract The removal of corrosion products from bronze artifacts is still an open challenge, in particular when stubborn corrosion patinas are found on surfaces with pronounced cavities and reliefs. Highly viscous polymeric dispersions (HVPDs) of polyvinyl alcohol (PVA) are able to adhere to highly textured 3D surfaces, forming films that can be easily peeled off. Here, PVA-based HVPDs were loaded with tetraethylenepentamine (TEPA), whose copper(II) complex has a stability constant four orders of magnitude higher than that of EDTA tetrasodium salt, traditionally used by conservators for cleaning bronze. TEPA promotes alkaline hydrolysis of acetyl groups in PVA, leading to the association of the polymer chains into more ordered structures, reducing significantly the time needed for the formation of films as compared to HVPDs loaded with water. Besides, the solubility of TEPA in most polar solvents allows to upload higher quantities of chelating agent in the HVPD, as opposed to EDTA. The confinement of TEPA inside the PVA matrix allowed the effective and progressive removal of copper corrosion products from a 16th century Italian bronze masterpiece, preserving the natural cuprite patina of the historical bronze, in times drastically shorter than traditional cleaning methods.