Investigation of phase transitions in vegetable oils through temperature-dependent optical measurements: supercooling effect

Measurements of the phase transitions in vegetable oils such as coconut, palm (fruit), palm kernel (from the seeds), macauba (Acrocomia aculeata) and its biodiesel have been taken through temperature-dependent optical transmittance. Room-temperature optical transmittance spectroscopy experiments in the UV–Vis–NIR region showed that oils begin to transmit at different wavelengths and present different wavelength rates of light transmission. A peak level of absorption at 930 nm is present for all samples and attributed to the third harmonic of vibrational mode of chemical groups with covalent C–H bonds. Viscosity and density measurements of the vegetable oils and biodiesel were also carried out in order to aid in the interpretation of their thermal behavior. The phase transition regions were determined, and the supercooling effect was detected in the oils due to their high viscosity. The effect was not observed in the macauba biodiesel due to its low viscosity.