Oil-in-Water Nanocontainers as Low Environmental Impact Cleaning Tools for Works of Art:  Two Case Studies

Abstract

A novel class of p-xylene-in-water microemulsions mainly based on nonionic surfactants and their application as low impact cleaning tool in cultural heritage conservation is presented. Alkyl polyglycosides (APG) and Triton X-100 surfactants allow obtaining very effective low impact oil-in-water (o/w) microemulsions as alternatives to pure organic solvents for the removal of polymers (particularly Paraloid B72 and Primal AC33) applied during previous conservation treatments. The ternary APG/p-xylene/water microemulsions have been characterized by quasi elastic light scattering to obtain the hydrodynamic radius and the polydispersity of the microemulsion droplets. Laplace inversion of the correlation function CONTIN analysis provided evidence of acrylic copolymers solubilization into the oil nanodroplets. Contact angle, Fourier transform infrared (FTIR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) data confirmed that microemulsions were effective in removing polymer coatings. The phase diagram of APG microemulsions showed that a reduction >90% (compared to the conventional cleaning methods) of the organic solvent can be achieved by using o/w microemulsions. The microemulsions were successfully tested in two real cases: (1) the APG based microemulsion was used in a Renaissance painting by Vecchietta in Santa Maria della Scala, Siena, Italy, degraded by the presence of a polyacrylate coating applied during a previous restoration and (2) a Triton X-100 oil-in-water microemulsion containing (NH 4 ) 2 CO 3 in the water continuous phase. The association of ammoniun carbonate to the microemusion led to the swelling of an organic deposit (mainly asphaltenes deposited on the fresco in the Oratorio di San Nicola al Ceppo in Florence, still contamined by the water of the Arno river during the 1966 flood) and a very efficient removal of highly insoluble inorganic deposits (mainly gypsum) strongly associated to asphaltenes. These innovative systems are very attractive for the low amount of organic solvent used to extract the polymers or highly insoluble substances as the asphaltene and the very efficient and mild impact of the cleaning procedure on the fragile painted surfaces.

Partially hydrolyzed poly(vinyl acetate)-borax-based gel-like materials for conservation of art: Characterization and applications

“…Conservators now have options ranging from sponges, erasers, and dust cloths in the mechanical cleaning realm, to Nd:YAG lasers in the noncontact field (Nevin et al, 2007;Pouli et al, 2010;Siano et al, 2012). The chemical cleaning sphere has shown the greatest diversity, however, where both aqueous and organic systems have been expanded to include soaps (Erhardt & Bischoff, 1994), surfactant and buffer solutions (Wolbers, 2000;Stavroudis et al, 2005), chelating agents (Carlyle et al, 1990;Phenix & Burnstock, 1992), active enzymes in free or gelled forms, emulsions and microemulsions (Carretti et al, 2007;Giorgi et al, 2010;Keefe et al, 2011), poultices, Carbopol gels (Wolbers, 2000;Dorge, 2004), agar gels (Warda et al, 2007;Gorel, 2011), and responsive, rheoreversible physical gels containing organic solvents, micro-micellar solutions, and magnetic nanoparticles (Carretti et al, 2010a;Pizzorusso et al, 2012). The toolbox of the conservator is now very large and diversified, and additional materials are becoming available annually.…”

Innovative Nanomaterials: Principles, Availability and Scopes

“…1.3 Nanostructured Cleaning Fluids Starting from that pioneering study, several systems have been prepared characterized and successfully applied for the removal of undesired materials from artistic surfaces. Numerous examples are reported by the literature, see for instance Baglioni et al (2011) and Carretti et al (2003Carretti et al ( , 2007, making nanostructured fluids one of the most appealing advanced cleaning tools for Cultural Heritage conservation, together with gels (see Sect. 1.4), laser technology (Nevin et al 2007;Siano and Salimbeni 2010;Pouli et al 2010), and the promising "biocleaning" based on the use of microorganisms (Cappitelli et al 2006;Alfano et al 2011).…”

“…• In several practical applications, nanostructured fluids can remove effectively detrimental coatings that can not be dissolved by conventional solvents (e.g. acetone, benzyl alcohols and xylenes), or that would require the use of aggressive and toxic solvents (Carretti et al 2007;Baglioni et al 2012). This is due to the structure and chemical composition of the surfactant-based fluids, and to the mechanisms through which they interact with organic coatings (the interaction will be further described in Sect.…”

Cleaning of Wall Paintings and Stones

“…Alkyl polyglycosides (APG) and ethoxylated alcohols belong to a class of "green" surfactants that possess interesting properties for a great number of applications, including cleaning of works of art (Luders 2000;Carretti et al 2007). More recently, fully biodegradable non-ionic surfactants (broad-or narrow-range ethoxylated alcohols, less than 7 %) were used to formulate a cleaning system, based on methyl ethyl ketone, ethyl acetate and butyl acetate (less than 5 % each).…”