Producción CyT
BOOK OF ABSTRACTS - An FTIR and GC/MS study on the formation of zinc soaps in aged oil paint models
Congreso
Autoría:
Astrid C. Blanco Guerrero ; Valeria P. Careaga ; Norielys Herrera Rivas ; Millán, Isabel Alcántara ; Gabriela Siracusano ; Marta S. MaierFecha:
2023Editorial y Lugar de Edición:
Universidade Nova de Lisboa - Faculdade de Ciências e TecnologiaResumen *
Zinc salts of fatty acids (zinc soaps) are degradation products formed by reaction of an oilbinder and zinc oxide used as pigment or ground in paintings. Their presence is associatedwith changes in the appearance and structural stability of oil paintings, such as surfaceefflorescence, delamination and paint transparency. During polymerization and oxidation ofdrying oils, two different phases of zinc soaps are formed: amorphous ionomers andcrystalline polymorphs of saturated mono and diacids. The presence of these species can becharacterized by infrared spectroscopy [1].This study focuses on the reactivity of zinc oxide with four drying oils used in modern oilpaints: linseed oil, walnut oil, sunflower oil and safflower oil. Mock-ups were prepared bymixing artist grade zinc oxide (Cornelissen) with oil in a 1:1 w/w ratio and application onglass slides. The paint mock-ups were aged in two conditions: at room temperature andexposed to UV light with a maximum at 370 nm (1627 µW/cm2, 22 °C and 42 % RH).Samples were removed periodically from the mock-ups and analized by ATR-FTIRspectroscopy. Zinc soaps obtained by saponification of the four oils, acidification and reactionwith zinc acetate were used as references. Linseed oil revealed the formation of ionomericzinc soaps after 15 days of exposure at room temperature, while walnut oil formed crystallinesoaps as indicated by the presence of two bands at 1527 and 1545 cm-1 in the IR spectrum [1].Sunflower and safflower oil mock-ups did not show significant changes up to 2 months ofexposure. UV ageing of the mock-ups revealed a similar trend as for natural ageing withsunflower and safflower oils being less reactive than linseed oil and walnut oil. After 40 hsUV ageing, sunflower and safflower oils showed very weak bands at 1559 and 1506 cm-1 thatshifted to a broad peak centered at 1571-1574 cm-1 after 100 hs ageing, which is characteristicof a zinc soap ionomeric phase. This band remained unchanged after 4000 hs UV ageing.Walnut oil showed a broad band with two overlapped peaks at 1530 and 1553 cm-1 after 40 hsageing, which shifted to a band at 1580 cm-1 after 100 hs ageing. Linseed oil showed a broadband with a peak at 1562 cm-1 after 40 hs of ageing that shifted to a ionomer phase band at1580 cm-1 after 100 hs ageing and remained unchanged after 4000 hs.Samples extracted from the mock-ups after 4000 hs UV ageing were analyzed by GC-MSapplying a three step procedure using two different silylating reagents to identify free fattyacids and zinc soaps [2] as well as trimethylsulfonium hydroxide (TMSH) to characterizefatty acids from remaining triacylglycerides in the aged samples.[1] M. Beerse, K. Keune, P. Iedema, S. Woutersen, J. Hermans, Applied Polymer Materials 2, 2020, 5674.[2] J. La Nasa, A. Lluveras-Tenorio, F. Modugno, I. Bonaduce, Heritage Science 2018, 6:57 Información suministrada por el agente en SIGEVAPalabras Clave
PAINT MODELSGAS CHROMATOGRAPHY- MASS SPECTROMETRYFTIR-ATRZINC SOAPS