High temperature interactions of lead palmitate with linseed oil

Abstract

This study investigates the high-temperature interactions between lead palmitate (Pb(C16)₂) and linseed oil, revealing complex phase transformations and structural changes critical for understanding metal soap formation in oil paintings. Through complementary analytical techniques including DSC, XRPD, FTIR, and solid-state NMR, we identified two significant phenomena: the formation of mixed lead palmitate–stearate compounds and the emergence of a high-temperature lead palmitate polymorph. When heated to 112 °C, lead palmitate in linseed oil undergoes partial conversion to mixed lead palmitate–stearate complexes, likely due to interactions with stearic acid present in the oil either in a free form or as a part of triglycerides. Additionally, we observed the formation of a metastable high-temperature polymorph characterized by hemi-directed coordination around lead atoms, similar to structures found in short-chain lead carboxylates. The transformation kinetics of this polymorph appears as a complex process influenced by several factors. These findings provide crucial insights into the behavior of lead soaps in oil paintings during thermal treatments and contribute to our understanding of metal soap-induced degradation in artistic and cultural heritage materials.