Novel formulations of polyvinyl alcohol-based peelable systems for the cleaning of metal artefacts

The presence of dirt, soil, aged polymers or corrosion patinas can hinder the readability of artworks; in these cases, non-invasive and controlled removal is essential. Nanostructured fluids (NSFs) - such as micellar solutions and microemulsions- allowed achieving this purpose, decreasing, at the same time, the drawbacks related to the use of solvents. In the last decades, several cleaning fluids have been developed; surfactants, in particular, have a crucial role in the NSFs’ formulations. For this reason, the research of innovative and highly performing amphiphiles represents one of the main goals in modern conservation science, in order to develop safer and greener systems. Two different NSFs were prepared with MPD surfactant and their interaction with soil and polymeric layers was evaluated through several techniques (CLSM, photographic observation, contact angle and surface tension measurements). Moreover, a comparison with a conventional nonionic surfactant (PDE) was made. MPD-based NSFs were found to be more effective in cleaning surfaces, also without mechanical action. Confining cleaning fluids in retentive matrices like gels represents one of the most powerful strategies to obtain greater control of the cleaning action. Two different pHEMA-based semi-IPNs were used as scaffold for a high selective agent (i.e., TEPA) able to remove corrosion products without affecting the protective cuprite layers. Changes in gels’ structure were evaluated by means DSC, TGA and SEM analysis before and after the interaction with the copper alloys; Cu(II) ion adsorption kinetics were used to assess the effect of the gels’ structure on the adsorption process. The pHEMA-based gels, classified as “rigid systems”, are not suitable for the treatment of bronze sculpture characterized by deep cavities and high reliefs. To overcome these limitations, TEPA was confined into a PVA-based film (HVPD) forming system. Thanks to its viscoelastic properties and its ability to combine a chemical action with a mechanical one, the HVPD represents a good option in these cases. The physico-chemical characterization was carried out to evaluate the effect of TEPA-addition on (1) the kinetics of the film formation, quantified through gravimetric and rheological measurements, and on (2) the final films’ properties, determined by DSC, ATR-FTIR and SEM analysis. 2D FTIR FPA Imaging confirmed the complete removal of corrosion products, the preservation of cuprite layers and the absence of residues on the mock-up surfaces after the treatment with both semi-IPNs and HVPDs. Finally, tests on real cases study are presented.