Thermal Behavior of the Divalent Metal Soaps of Flax, Hemp, and Safflower Seed Oils

Abstract

This study investigated the thermal behavior of metal (barium, calcium, and zinc) soaps of flaxseed (FSO), hemp seed (HSO), and safflower (SFO) oils. The soaps were prepared by metathesis in an alcohol solution and characterized using the infrared (IR) spectroscopic technique, thermal methods, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) measurements. Features that are characteristic of specific compounds were observed from the IR graphs. The thermal behavior of the soaps was examined by simultaneous thermogravimetry, differential thermal analysis, and derivative thermogravimetry (TGA, DTA, and DTG, respectively), and it was found that degradation of the metal soaps was a multistep process: melting followed by decomposition. The percentage mass loss at various temperatures and residual mass at 600 °C were used as the indicators of the thermal stability of the metal soaps. The results showed that metal soaps obtained from different vegetable oils with the same metal ion showed differences, as did metal soaps obtained with the same vegetable oil but with different metal ions. The barium soap of SFO appeared to be more thermally stable than the other divalent metal soaps. The metal soaps show an irregular morphology with somewhat elongated plate-like structures, possibly from various multistructural groups in the soap matrix.