AIC's 41st Annual Meeting, Paintings and Research and Technical Studies Joint Session, May 31, "Water in Oil Microemulsions: A Novel Cleaning System for Acrylic Paints" by Tom Learner, et al

This presentation summarized the collaborative research of the cleaning of acrylic paint films by the authors representing the DOW Chemical Company, the Tate Gallery and the Getty Conservation Institute.  The aim of the research is to develop and educate professionals in the cleaning of complex, contemporary synthetic painting media. Early findings of this research have been presented at the AIC Annual Meetings in Los Angeles (2009) and Milwaukee (2010) and at the Cleaning 2010 Conference in Valencia.  The components of these systems have varying effects on the medium: acrylic paint films are easily swollen in an aqueous environment, hydrocarbons have poor cleaning efficacy and on large colored surfaces there is a risk of tidelines.  The surface character can be changed if extracts are removed.
Dynamic mechanical analysis of potential cleaning materials was conducted; the procedural process was described as “clamping” system that would provide uniform tension across the test film as it was dipped in solution.  The displacement of the grips is measured as the paint film contracts upon drying.  Acetone and water produced significant swelling, mineral spirits resulting in a flat line.  Analysis was conducted using FTIR-ATR (Fourier transform infrared-attenuated total reflectance) spectroscopy on cleaning swabs indicating the level of surfactant material at the surface.
Trial microemulsion cleaning formulations were prepared by DOW and the Tate which were tested by conservators at workshops,  including four CAP’s (Cleaning Acrylic Paintings) seminars presented in different cities by Chris Stravroudis.  Resulting evaluations have contributed to further refinement of formulations for better compliance with performance criteria desired by conservators.  Three classes of microemulsions were produced.  All have an aliphatic hydrocarbon in a continuous phase.  They incorporate different surfactants.  The presence/level of an alcohol as a co-solvent is sometimes incorporated, as an alcohol is required in some systems to enable a stable microemulsion structure.  One class of potentially useful formulations of water-in-oil microemulsion systems that are thermodynamically stable is being tested. They incorporate deionized water, a non-miscible hydrocarbon solvent (one being tested is hexanol/butanol (?)) and a surfactant in an attempt to remove grime without removing original material, namely surfactants used in the manufacture of these painting materials, which are known to migrate to the surface as they age. They offer the possibility of exploiting cleaning efficacy associated with aqueous systems but in a predominantly solvent environment where the micelles formed has the surfactant on the outside and the water on the inside. The pH in these systems can be varied using sodium chloride.  The ionic strength of the solution should be compatible with the paint film; conductivity should be adjusted, as needed.  A stable microemulsion will be clear, while an unstable one will be milky.  Other components of the three series included a “green” surfactant, Ecosurf®, a promising new Triton material, Triton GR7, which is soluble in Shell Sol solvents, and the introduction by Richard Wolbers of silicon based cleaners.  The latter material was reviewed by Chris Stravroudis in his article, “More from CAPS3: Surfactants, silicone-based solvents, and microemulsions”, WAAC Newsletter 34/3 (Sept 2012), pp 24-27.
The series of microemulsions are being extensively tested including the issue of clearance.  A new publication on the progress of this research is expected in 2014.