Effect of high-pressure gases on phase behaviour of solid lipids

The effects of CO2, CHClF2 and CH2FCF under pressure on solid lipids were addressed by high-pressure differential scanning calorimeter (HP DSC). In particular, the influence on solid–liquid and solid–solid transitions were investigated for pure tristearin and a mixture of lipids (tristearin–phosphatidylcholine–dioctyl sulfosuccinate). Both of these substances are commonly used for the production of solid–lipid–nano-particles [1], [2] and [3]. The experiments were carried at different operating pressures up to 7.0 MPa. The melting and solidification temperatures were measured for six gas–lipid systems.Interestingly, a hysteresis was observed in the solid–liquid and liquid–solid transitions. In addition, the formation of alpha and beta polymorphisms that are typical for lipids, were found to be affected by the system pressure. With regard to the experiments with CO2, the results indicate a melting point depression as function of the gas pressure, up to 6 MPa. A similar trend to CO2 was obtained using CHClF2 at a lower pressure (0.75 MPa), however CH2FCF3 exhibits a weaker effect on the melting temperature depression compared to CHClF2.These results indicate the possibility of processing liquid lipids and similar thermosensitive compounds in gas-assisted micronization processes under mild temperature conditions.