Nanostructured Fluids For Polymeric Coatings Removal: Surfactants Affect the Polymer Glass Transition Temperature
Hypothesis: Nanostructured fluids (NSFs) based on water, organic solvents and surfactants are a valid alternative to the use of neat unconfined organic solvents for polymer coatings removal in art conservation. The physico-chemical processes underpinning their cleaning effectiveness in terms of swelling/dewetting of polymer films were identified as key in this context. The role of surfactants on polymers’ dewetting was considered to be mainly restricted to the lowering of interfacial tensions. However, recent experiments evidenced that surfactants have an important role in swelling polymer films.
Highlights
Nanostructured fluids are used to remove polymer coatings in art conservation.
Polymer films are either dewetted or swollen depending on their composition.
Surfactants have an important role in swelling polymer films.
Polymer swelling depends on the polymer glass temperature change induced by surfactants interaction with polymer films.
Nonionic are more efficient than zwitterionic/ionic surfactants in lowering the Tg.
Experiments: Five different amphiphiles were selected, namely: sodium dodecylsulfate, dimethyldodecyl amine oxide, hexaoxyethylene decyl ether (C9-11E6), pentadecaoxyethylene dodecyl ether (C12E15), and methyoxypentadecaoxyethylene dodecanoate (C11COE15CH3). They were combined with a carefully selected organic solvents’ mixture (1-butanol/butanone/dimethyl carbonate) to formulate new NSFs, differing for the surfactant only, and used to perform cleaning tests on surfaces coated with Paraloid B72® and Primal AC33®. Here for the first time, polymer swelling induced by surfactants was quantified and correlated with the glass transition temperature of the two polymers by differential scanning calorimetry, before and after the exposure to the fluids. Confocal laser scanning microscopy and small-angle X-ray scattering provided additional insights on the interaction mechanism.
Findings: Nonionics were proven more efficient than zwitterionic/ionic amphiphiles in the polymer swelling, and, overall, methyoxy pentadecaoxyethylene dodecanoate resulted the most effective among the selected surfactants. A direct relation between the polymer/surfactant glass transition temperature and cleaning capacity was established. This finding, fundamental to understand the interaction mechanism between NSFs and polymer coatings or paint layers, is key to achieve a selective, effective and complete removal of polymer coatings, as recently shown in the removal of vandalism and over-paintings from street art.
Article information: Michele Baglioni, Felipe Hidetomo Sekine, Taku Ogura, Sow-Hsin Chen, Piero Baglioni, Nanostructured Fluids For Polymeric Coatings Removal: Surfactants Affect the Polymer Glass Transition Temperature, Journal of Colloid and Interface Science, 2021. https://doi.org/10.1016/j.jcis.2021.07.078.