Читать книгу Surface Science and Adhesion in Cosmetics - Группа авторов - Страница 26

Differential Scanning Calorimetry (DSC) measures the melting of the fats and oils in the sample to provide an idea of product performance [61]. This technique, referred to as fingerprinting, provides information regarding product wear and performance as a direct relation to peak shape, size, and temperature after being run on a single furnace, heat flux DSC [61]. We can look at the signature peaks from the DSC readout to help characterize the type of wax and expected consumer sensory. This method is ideal for long-wear sticks as the isododecane helps keep the stick soft and acts as a solvent for the different waxes in the formulation. Typically, liquid format long-wear lipsticks are not preferred for this method as there is a very small amount of wax in the formulation, making it hard to fingerprint.

A sample profile can be seen in Figure 1.8. In this experiment, 30mg of samples for lipstick formulations A, B, C, and D were placed in hermetically sealed aluminum pans and were ramped from -100°C to 100°C at a rate of 2°C/minute to obtain the full DSC profile of the sample [61]. The figure demonstrates that there are melting peaks between 25°C to 50°C, indicating that the samples will spread on warm surfaces, such as the lips [61]. The location of the peaks can help to identify the type of wax used in the formulation; for example, in Formulation D in Figure 1.8, we can conclude that different waxes that have a higher melting temperature and must be harder compared to Formulations A-C due to the location and intensity of the peaks. Peaks located at higher temperature indicate that the formulation may be more difficult to apply to the lip due to its lower temperature, but once applied will stay longer [61].

This provides further insight into the application process experienced by consumers. Softer formulations will melt on the lip during application but will still be hard enough to resist snapping when used; this provides a positive sensory experience for the consumer.