Evolution of Zinc Carboxylate Species in Oil Paint Ionomers

Oil paint binding media are complex
polymer networks that harbor
populations of metal ions. Understanding of the reactivity of these
metal ions, often closely linked to paint degradation, is crucial
to support paintings conservation efforts. By developing a spectrum
fitting approach for the analysis of Fourier transform infrared spectra,
we have studied in detail how the molecular structures of zinc carboxylate
species in oil paint ionomers change in the lifetime of a painting.
It was found that high ZnO pigment content, humidity, and low paint
viscosity all stimulate the formation of ionomeric zinc carboxylate
species, while the structures (chain or oxo) adopted by those species
depend on carboxylate concentration and humidity. Moreover, we found
evidence for a difference in reactivity between the two structures
for ionomeric zinc carboxylates toward the formation of crystalline
zinc soaps. The results have yielded an abundance of information about
the internal chemistry of oil paint layers and metal-containing polymers
in general.