Technological study of kaolinitic clays from Fms. Escucha and Utrillas to be used in dermo-pharmaceutical products

The present study aims to evaluate five clay samples from different pits in the Teruel province, Spain. While these clays are primarily utilized as raw materials in ceramics, their potential applications in pharmaceutical and cosmetic domains, notably in sun protection and thermal mud products, are under investigation. Characterization of these clays entailed X-ray diffraction, X-ray fluorescence, scanning electron microscopy, pH measurement, analysis of technological properties, rheological assessment, and thermal property evaluation. Furthermore, given the predominant composition of kaolin in most of the samples, their Sun Protection Factor (SPF) in suspensions and physical stability were assessed. The studied samples exhibited varied mineralogical compositions, primarily consisting of kaolinite (70% to 15%), quartz (75% to 5%), and illite (26% to 7%). The pH values of these dispersions closely matched the skin's pH, exhibiting anti-thixotropic behavior at 50% w/w and demonstrating suitable viscosity for skin application. Based on their composition and rheological properties, the samples exhibited potential for use as therapeutic thermal muds. Analyses of cooling kinetics were performed to validate this potential. Results showed that the dispersions systems attained temperatures between 33.89 ◦C and 34.62 ◦C within 20 min (the common application time for thermal muds) and reached 32 ◦C (skin temperature) in 24.3 to 26.22 min, confirming their appropriateness as therapeutic muds. The SPF values of the dispersions varied from 7.46 to 16.65, with the majority of samples showing significant stability during 45 h. Consequently, it can be inferred that most of the studied samples show advantageous characteristics for inclusion in topical formulations, especially in sun protection and thermal mud products.