Physical Properties of Epoxidized Vegetable Oils

Epoxidized vegetable oil (EVO) is an important biorenewable molecule, either on its own or as a precursor to other biobased compounds.  Epoxy groups are added to vegetable oils (triglycerides) by oxidation of their naturally occurring double bonds. Currently, the vast majority of EVO is produced from commodity-grade soybean oil (SBO), rich in linoleic acid and averaging 4.6 double bonds per molecule. With the impending shift of soybean production to high oleic varieties due to nutritional concerns, there is a likelihood that the availability of SBO will be drastically diminished in favor of High Oleic Soybean Oil (HOSBO). However, little is known about the role of the fatty acid composition on the chemical and physical properties of the derivative EVO. In this work three different EVOs were studied originating from SBO, HOSBO, and linseed oils (LO); these oils contain 4.6, 3, and 6.4 double bonds per molecule respectively. The viscosity and thermal properties were measured as a function of the initial unsaturation level and final epoxidation level.  Viscometry and DSC were chosen as analytical methods. We found that HOSBO has the highest viscosity and activation energy among the three. Also, viscosity and activation energy tended to increase as the conversion of double bonds to epoxy rings increased for all oils, due to the increase in dipole-dipole intermolecular forces.   DSC showed a general increase in crystalline temperature as conversion increased, due to increased intermolecular forces and the straightening of the fatty acid chains and better packed structures as the double bonds break.  However, epoxidized HOSBO showed a more crystalline structure than the other epoxidized oils due to a more consistent composition.