Unexpected behavior of commercial artists’ acrylic paints under UVA artificial aging

• Published in: Microchemical journal 2021-01, Vol.160, p.105743, Article 105743
• Main Authors: Aguilar-Rodríguez, Pablo, Mejía-González, Adrián, Zetina, Sandra, Colin-Molina, Abraham, Rodríguez-Molina, Braulio, Esturau-Escofet, Nuria
• Format: Article
• Language: English
• Subjects: Acrylic emulsion paints; FTIR-ATR; Liquid-state NMR; SEM-EDS; Solid-state 13C CP-MAS NMR; UVA aging
• ISSN: 0026-265X; 1095-9149
• DOI: 10.1016/j.microc.2020.105743

•Multi-analytical approach for the characterization of acrylic paints.•Influence of UV-A ag-ing on physicochemical properties of acrylic paints.•Pictorial layer study by optical microscopy and SEM-EDS.•Chemical elucidation by the combination of Py-GC/MS, NMR, FTIR-ATR and DART-MS.•Study of the molecular mobility of aged paint by 13C CP-MAS NMR spectroscopy. The study of the behavior of acrylic paints after UV-A (400–300 nm, near UV) artificial exposure was further investigated by extending it to more commercially available artists’ acrylic paints. The accelerated aging of eight acrylic-based commercial paints was studied using a combination of analytical techniques including Nuclear Magnetic Resonance (NMR) spectroscopies, Pyrolysis coupled with Gas Chromatography/Mass Spectrometry (Py-GC/MS), Fourier Transform Infrared in ATR mode (FTIR-ATR), Direct Analysis in Real Time coupled to Mass Spectrometry (DART-MS) and microscopic techniques, such as Stereoscopic Microscopy (SM) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). All the aging process was characterized and monitored to study the signs of decay. During the aging process a gradual loss of the organic surfactant occurred in all the paints, similar to the results contained in a previous study. Interestingly, two of the studied paints presented an unexpected behavior related to the properties of the acrylic binder. In one of such paints solid-state 13C Cross Polarization Magic Angle Spinning (13C CPMAS) NMR spectroscopy was performed. The results obtained by changing the recycled delay and carrying out variable temperature experiments, suggested a change in the internal mobility of the aged sample that could be attributed to the presence of ionomers. According to this study, the aging of acrylic binders may not be the same in all paints and may be affected by the interaction of different components of the formulation. Understanding these processes will give more tools for the preservation of modern art paintings and cultural heritage since this type of commercial paints and other conservation materials of the same composition were extensively used during the 20th century.