Crystallization kinetics of fully hydrogenated palm oil in sunflower oil mixtures

The crystallization kinetics of mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF) was studied. The thermal properties and phase behavior of this model system were characterized by means of differential scanning calorimetry and X-ray diffraction. From the melting enthalpy and clear point of HP, it was possible to calculate the supersaturation at a given temperature for every composition of the model system. Supersaturation of the model system for the beta' but not for the a polymorph yielded the beta' polymorph, while supersaturation for the a polymorph yielded a mixture of mainly beta and some beta' polymorphs. The crystallization kinetics of HP/SF mixtures were determined by pulsed wide-line proton nuclear magnetic resonance for various initial supersaturations in the beta' polymorph. The determined curves were modeled by a modified classical nucleation model and an empirical crystal growth function, which are both functions of supersaturation. Heterogeneous nucleation rates in the beta' polymorph yielded a surface Gibbs energy for heterogeneous nucleus formation of 3.8 mJ.m(-2). About 80% of the triglyceride was assumed to be in a suitable conformation for incorporation in a nucleus. Induction times for isothermal crystallization in the beta' polymorph yielded a surface free energy for heterogeneous nucleus formation of 3.4 to 3.9 mJ.m(-2).