Solubilization of acrylic and vinyl polymers in nanocontainer solutions. Application of microemulsions and micelles to cultural heritage conservation

This study reports the physicochemical investigation of oil-in-water (o/w) microemulsions and micellar solutions formulated to solubilize acrylic and vinyl polymers. Three different four-component systems formed from (i) water, p-xylene, sodium dodecylsulfate, and 1-pentanol; (ii) water, propylene carbonate, sodium dodecylsulfate, and 1-pentanol; and (iii) water, p-xylene, Tween-20, and 1,2-ethandiol, and one five-component system (water,p-xylene, commercial nitro-diluent, sodium dodecylsulfate, and 1-pentanol) have been studied. The o/w microemulsions or micellar solutions (system ii) have been characterized by quasi-elastic light scattering experiments to obtain the hydrodynamic radius and the polydispersity of the microemulsion or micelle droplets. The application of these microemulsion or micellar systems as solubilizing agents for acrylic and vinyl polymers from works of art (mainly wall paintings) and monuments (stones) has been investigated. Acrylic and vinyl polymers have been extensively used in the past decades, and are still used, for art conservation. The aging produced both yellowing and serious degradation of the painted layers or of the stone surfaces, imposing their removal from the artistic and architectonic surfaces. Contact angle measurements, FTIR, and SEM/EDX results showed that the microemulsions and micellar solutions investigated were very effective in removing acrylic or vinyl polymeric resins from several solid surfaces. Hydrophobic acrylic copolymers have been completely removed from a Renaissance fresco by Spinello Aretino (used during a restoration performed in the sixties) in the Cappella Guasconi in San Francesco Cathedral, Arezzo, Italy, and poly(vinyl acetate) resins (used in a restoration performed during the fifties) from Renaissance frescoes decorating the external walls of the Cathedral of Conegliano, Northern-East Italy. The nanocontainers route represents a new, safe, and very efficient method for removing aged polymer from surfaces of works of art, otherwise condemned to complete loss.