The Phase Space of Crystallization: Modeling Fat Crystallization Using Thermodynamic and Mass-Transfer Variables

The following work describes the application of a conceptual tool, the “phase space”, to describe the trajectory of crystallization in a space defined by thermodynamic and mass-transfer variables. Three materials and two crystallization conditions were studied: a fast-cooling condition and a slow-cooling condition. The phase space trajectories showed that the higher the viscosity at the start of crystallization (i.e., lower crystallization temperature), the smaller the resulting crystal size, due to limited crystal growth as a result of impeded mass transfer. Likewise, a lower viscosity at the start of crystallization resulted in larger crystal sizes. Charting the trajectory of crystallization for two polycrystalline triglyceride fats in a triglyceride oil, namely fully hydrogenated soybean oil (FHSO) in soybean oil and FHSO in high oleic sunflower oil, also showed that the material exhibited an excess crystallization in that the initial crystallization created more solid material than was predicted from chemical potential considerations of the most stable polymorph. Subsequently, the solid content decreased over time in storage. DSC and X-ray diffractometry were used to characterize the material during crystallization and after storage, respectively. Collectively, these showed that the apparent excess crystallization detected in the phase trajectories was attributable to a polymorphic transformation.