Nanostructured fluids for polymeric coatings removal: Surfactants affect the polymer glass transition temperature

Michele Baglioni; Felipe Hidetomo Sekine; Taku Ogura; Sow-Hsin Chen; Piero Baglioni

doi:10.1016/j.jcis.2021.07.078

Nanostructured fluids for polymeric coatings removal: Surfactants affect the polymer glass transition temperature

J Colloid Interface Sci. 2022 Jan 15;606(Pt 1):124-134. doi: 10.1016/j.jcis.2021.07.078. Epub 2021 Jul 29.

Authors

Michele Baglioni¹, Felipe Hidetomo Sekine², Taku Ogura³, Sow-Hsin Chen⁴, Piero Baglioni⁵

Affiliations

¹ Department of Chemistry and CSGI, University of Florence, via della Lastruccia, 3, Sesto Fiorentino (FI) 50019, Italy.
² NIKKOL GROUP Nikko Chemicals Co., Ltd, 1-4-8, Nihonbashi-Bakurocho, Chuo-ku, Tokyo 103-0002, Japan.
³ NIKKOL GROUP Nikko Chemicals Co., Ltd, 1-4-8, Nihonbashi-Bakurocho, Chuo-ku, Tokyo 103-0002, Japan; NIKKOL GROUP Cosmos Technical Center Co., Ltd, 3-24-3 Hasune, Itabashi-ku, Tokyo 174-0046, Japan; Research Institute for Science & Technology, Tokyo University of Science, 2641, Noda-shi, Chiba, Yamazaki 278-8510, Japan.
⁴ Department of Nuclear Science & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139, USA.
⁵ Department of Chemistry and CSGI, University of Florence, via della Lastruccia, 3, Sesto Fiorentino (FI) 50019, Italy; Department of Nuclear Science & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139, USA. Electronic address: piero.baglioni@unifi.it.

PMID: 34390987
DOI: 10.1016/j.jcis.2021.07.078

Abstract

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.

Experiments: Five different amphiphiles were selected, namely: sodium dodecylsulfate, dimethyldodecyl amine oxide, hexaoxyethylene decyl ether (C_9-11E₆), 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 effect of surfactants on the polymers' 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.

Keywords: Art conservation; Cleaning; Complex fluids; Cultural heritage; Dewetting; Glass transition temperature; Microemulsions; Polymer; Sodium dodecylsulfate; Tg.