The usage and safety of cosmetic products are significantly influenced by their stability, which must be ensured throughout the entire shelf life, during storage and transport from the manufacturer to the consumer. With stability studies we ensure their physical, chemical and microbiological quality, functionality and aesthetic properties under normal storage conditions. Because of diversity and complexity of cosmetics, standard tests are not available. The manufacturer has to design them himself, with consideration of products characteristics and his professional judgment. Physical instability often causes problems during design development and manufacture of cosmetics, as well as during the transport, storage and their usage. The causes can be various factors, such as unsuitable design development, manufacturing design, distribution, usage and inappropriate storage of the product. In the diploma thesis, we used a method for accelerated stability testing of disperse systems physical stability by application of mechanical vibrations, which could show signs of instability in a short period of time and could also reduce the scope of further testing. We tested the emulsion systems of selected products, manufactured by the company Ilirija d.o.o. Stable and unstable formulations of the same products, which had already been tested with different accelerated and long-term tests by the company, were put under stressful vibrating conditions. After 6 hours of exposure to mechanical vibrations at 25 °C and the amplitude of 80%, comparable results were obtained with rotational testing and polarization microscopy, therefore the method proved to be suitable. Stereomicroscopy, oscillatory testing and organoleptic evaluation have proved to be unsuitable as test methods in this case, because the obtained data was not uniform and representative enough. Samples were not exposed to vibrations in the heat chamber, as they were found to be hypersensitive to elevated temperatures, such as 40 °C, by means of differential dynamic calorimetry (DSC). Testing could be used for the stability testing of only such disperse systems whose components do not physically change at elevated temperatures.
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