Biocleaning of acrylic materials

In a restoration, conservation and enhancement of Cultural Heritage project, the cleanup phase is one of the earliest and most delicate operations for the removal of dirt, black crusts, consolidating, protective coatings used in past restorations or, finally, of spray paints. The goal of this study has been to verify the effectiveness of an environmentally sustainable biocleaning method using enzymes, such as lipases, for removing acrylic-based materials. The lipases purchased are extracted from fungi such as Candida rugosa (Type VII Sigma-Aldrich) and as Candida Antarctica (Sigma Aldrich), and various bacteria in a mix of lipase (CTS), and then applied on the specimens specifically prepared. The specimens are white ceramic substrates with a thin layer of different spray paints, markers and Paraloid, all based on acrylic. These materials were analyzed by Py-GC/MS, micro-Raman and FTIR spectroscopy in order to know the chemical composition of the formulations. Usually the spray paints and markers compositions are more complex because they consist of a binder, dyes and/or pigments and additives that confer to paint particular physico-chemical properties. The lipase action should hydrolyze the ester bond of the acrylic copolymers, transforming them from hydrophobic to hydrophilic compounds, facilitating their removal. The enzymes have been applied directly on the test specimens by employing both simple aqueous systems, or direct microemulsions in different conditions of time and temperature. The optimum activity of each lipase considered (pH and substrate concentration) was studied spectrophotometrically on a standard substrate.