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 behav ior of this model system were characterized by means of differential scanni ng calorimetry and X-ray diffraction. From the melting enthalpy and clear p oint of HP, it was possible to calculate the supersaturation at a given tem perature for every composition of the model system. Supersaturation of the model system for the beta' but not for the a polymorph yielded the beta' po lymorph, while supersaturation for the a polymorph yielded a mixture of mai nly beta and some beta' polymorphs. The crystallization kinetics of HP/SF m ixtures were determined by pulsed wide-line proton nuclear magnetic resonan ce for various initial supersaturations in the beta' polymorph. The determi ned curves were modeled by a modified classical nucleation model and an emp irical crystal growth function, which are both functions of supersaturation . Heterogeneous nucleation rates in the beta' polymorph yielded a surface G ibbs 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 incorp oration in a nucleus. Induction times for isothermal crystallization in the beta' polymorph yielded a surface free energy for heterogeneous nucleus fo rmation of 3.4 to 3.9 mJ.m(-2).