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    The influence of the SO2 ageing on the graffiti cleaning effectiveness with chemical procedures on a granite substrate

    Year: 2018

    Journal: Sci. Total Environ., Volume 625, JUN 1, page 233–245

    Authors: Gomes, Vera; Dionisio, Amelia; Santiago Pozo-Antonio, J.

    Organizations: Fundacao Calouste Gulbenkian [P202710]; Strategic project FCT [UID/ECI/04028/2013]; University of Vigo

    Keywords: Aerosol graffiti paints; SO2 ageing; Granite; Chemical cleaning; Effectiveness; Cultural heritage

    Graffiti are one of the most severe threats to Stone Cultural Heritage and are most of the times removed after long periods of environmental exposure. This research intends to evaluate the influence of the ageing of the graffitis on the effectiveness of their cleaning. So, comparative studies on unaged and on artificially SO2 aged samples were conducted. Four graffiti spray colours were applied on a granite stone and cleaned with two chemical commercial cleaners: a solution of KOH and a solution of n-butyl acetate, xylene and alcohol isobutyl. The spray paints (unaged and aged) and cleaning effectiveness were characterized by stereomicroscopy, colour spectrophotometry, adhesion tests, SEM, mu EDXRF, XRD and FTIR. The cleaning effectiveness was also evaluated through surface roughness and static contact angle measurements. The alkyd graffiti paints presented greatest resistance under SO2 rich environments than the polyethylene paint. The aged polyethylene paint showed chemical modifications that resulted in graffiti losses and neo formed mineralogical phases in the surface of the paint. After ageing, the paints became more difficult to clean, showed higher global colour changes and higher residue percentages. No significant roughness variations were detected after chemical cleaning. After the cleaning procedures aged surfaces became more water repellent comparatively to unaged and reference samples. The best cleaning effectiveness was mainly achieved with the potassium hydroxide solution. (c) 2017 Elsevier B.V. All rights reserved.
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