The thesis studies mixtures of alkanes, alkanols, and triglycerides that are used to provide structure to cosmetic products. These materials are blended together in such a way to create a product that is stable and rigid in the packaging, but deposits a thin film of material when rubbed on the skin. This research is driven by the industrial need to understand further the fundamental mechanisms occurring when the product is processed for the purpose of predicting scale-up behaviour. The aim of the project is to discover links between process conditions, crystallisation, polymorphism, physical properties and product performance.
The morphology, crystal structure, composition, thermal and physical properties of individual components, HCO, Petrolatum and 1-Octadecanol, was characterised using an array of analytical techniques including DSC, TGA, XRD, GC, SEM, AFM and Hot-Stage Microscopy. The properties of the three structuring materials were compared and contrasted to discover their role in the formulation.
Before studying the binary mixtures of 1-Octadecanol; HCO, solubility, thermodynamics and crystallisation kinetics of these materials were studied in a range of relevant non-polar and polar solvents including Dodecane, Undecane, Ethanol, Acetone and D5 using polythermal turbidity data. The data was analysed using van ‘t Hoff, and KBHR analysis and both materials were found to be most soluble in protic polar solvents and least soluble in non-polar solvents.
Binary mixtures have been studied through creating a series of phase diagrams using DSC and morphology, and mechanical property information has been superimposed with respect to composition using AFM. Binary mixtures of HCO and 1-Octadecanol have found to exhibit 4 distinct morphologies.
The final part of the project focused on the impact of shear and solvent on the crystal structure, polymorphism and rheology of the main structuring ingredient. Experiments using an online custom-made shear cell at a synchrotron allowed structural, rheological, and temperature data to be captured simultaneously, giving insight into mechanisms occurring during processing of the cosmetic products. The presence of shear and solvent has been found to induce phase separation of the rotator and gamma phases of 1-Octadecanol.
