Crystallization of sunflower oil waxes

Abstract

Activation free energies of nucleation (ΔGc) were calculated using induction times of crystallization measurements. Results showed that ΔGc decreased exponentially as wax concentration increased at a constant crystallization temperature (Tc). In contrast, for a constant supersaturation, ΔGc increased from 12 to 22°C but decreased between 22 and 35°C. Melting behavior of purified waxes and solutions of purified waxes in sunflower oil were studied by DSC after crystallization at fast and slow cooling rates (20 and 1 °C/min, respectively). Low supercooling temperatures (Tc > 65°C) showed an increase in the onset temperature (To) as Tc increased for both fast and slow cooling rates. Broader peaks were obtained for samples crystallized at a slow cooling rate at the same Tc. Regarding the solutions of waxes in sunflower oil, the wax concentration (supersaturation of the system) controlled crystallization as well as Tc. As Tc increased, the enthalpy (ΔH) decreased at a constant wax concentration. When wax concentration decreased, ΔH decreased at a constant Tc. For a low driving force, a small shoulder was obtained in the DSC diagrams owing to some type of fractionation. These results showed that wax crystallization is affected by different experimental parameters, such as Tc and cooling rate, depending on the wax concentration of the sample.