From inverse Pickering emulsion to polyhydroxybutyrate gel loaded with chelators for cleaning of copper surfaces: the stabilization effect of hydrophobized halloysite clay nanotubes

Among innovative gel formulations for metal conservation, a sustainable organogel based on bioderived polyhydroxybutyrate (PHB), ethyl lactate (EL) and chelating agents has been lately explored, bringing promising results. However, since ligands are usually found in the form of aqueous solutions, both the hydrophobicity of PHB and the not ideal mixture of EL in water should be considered. In this regard, we have developed a PHB-EL organo-gel, containing the chelating water solution in the form of a water-in-oil (W/O) Pickering emulsion stabilized by hydrophobized halloysite clay nanotubes (HNTs). The HNTs hydrophobization has been achieved by selective functionalization of outer surface with a cationic surfactant (hexadecyltrimethylammonium bromide). The stabilization mechanism of hydrophobized nanotubes to the inverse Pickering emulsion gels has been studied by combination of several methods, including morphological analysis, surface characterization and rheology. Then, the removal capacity of the gel systems toward corrosion layers from a copper substrate has been tested. Both the cleaning efficiency and the release of residues on the treated surfaces have been analyzed. A controlled cleaning has been obtained through the systematic regulation of the gel application time. Therefore, this work proposes an optimization of the previously studied organo-gel, obtaining a system with a more homogeneous structure due to the action of W/O Pickering emulsion.