The effect of TiO2 component on the properties of acrylic and urea-aldehyde resins under accelerated ageing conditions

Abstract

AbstractSynthetic resins were introduced in paintings conservation during the 1930s, as an alternative to natural resins, due to their superior resistance to degradation. Their composition usually includes a small amount of additives, such as titanium dioxide. The objective of this work is to study the effect of TiO2 additive on the durability of Paraloid B72 (acrylic resin) and Laropal A81 (urea-aldehyde condensation polymer), both used in art conservation, against photochemical degradation. A methodology involving separating particulate TiO2 from the organic fraction of the resins has been applied, followed by accelerated ageing of the resins in their commercial (C) and modified (M, i.e. after TiO2 removal) has been implemented. The morphological characteristics of resin films were examined through scanning electron microscopy (SEM). Chemical changes, colour properties and photo-chemical stability of the resins were studied with FTIR, UV-Vis absorption spectroscopy and spectro-colorimetry. The results showed a considerably different behaviour between the C and M states of both materials. In particular, C-Paraloid B72 collapses after prolonged irradiation, but within a certain time frame it appears to be relatively stable; on the other hand, C-Laropal A81 is considerably destabilized in comparison to its M state. It can be suggested that TiO2 acts as a UV-blocker for the underlying pigment layers, at the expense of resins’ stability.