Chemical and mechanical properties of drying oils during polymerization

Drying oils have been a common binding medium for paints since the 15th century. Oil paints transition from a liquid-like paste to a solid-like film via crosslink formation. These reactions have been studied chemically, but other material properties are not well characterized. Oil paints are used in composite structures where both mechanical and chemical properties matter. This thesis focuses on understanding the evolution of mechanical properties during drying oil polymerization.
Chapter 2 provides an overview of mechanical testing techniques used to study artists’ paints. The effects of composition, environment, and solvent exposure are discussed and newer techniques to monitor the evolution of mechanical properties are presented.
One challenge for most mechanical testing techniques is they cannot follow the evolution of mechanical properties during drying oil polymerization. In Chapter 3, the quartz crystal microbalance (QCM) can fill this gap, measuring changes in mass and mechanical properties during polymerization. Linseed oil samples are measured over several years of aging. Litharge is also incorporated, and its effects are quantified. The temperature dependent response of linseed oil is measured, and the lack of a well-defined glass transition temperature implies that there is nano-scale heterogeneity in the film.
Chapter 4 discusses using time-based attenuated total reflection infrared spectroscopy to obtain higher resolution of chemical changes occurring during polymerization. Five drying oils are measured and show chemical differences depending on the fatty acid distribution of the drying oil. Incorporating litharge results in a significant reduction of oxidation in the drying oil films.