Research Summary
Various methods of evaluating a humectant’s moisture retention have unique mechanisms. Hence, for designing advanced or efficient ingredients in cosmetic products, a clear understanding of the differences among these methods is required. The aim of this study was to analyze the moisture-retention capacity of glycerin, a common ingredient in cosmetic products. Specifically, this study applied gravimetric analysis, transepidermal water loss (TEWL) analysis, and differential scanning calorimetry (DSC) to examine the evaporation of glycerin solutions of different concentrations.
The results revealed that the moisture-retention capacity of glycerin increased with glycerin concentration from 0 to 60 wt%. Notably, glycerin at concentrations of 60–70 wt% did not exhibit any weight change during the evaporation process. When the glycerin concentration exceeded 70 wt%, moisture sorption occurred in the glycerin solution. Furthermore, the results revealed a deviation between the evaporation rates measured using gravimetric analysis and those measured using TEWL analysis. However, normalizing the results of these analyses yielded relative evaporation rates to water, which were consistent between the two analyses.
DSC thermograms further confirmed the consistent results and identified two hydrated water microstructures (non freezable water and free water) in the glycerin solutions. This finding explained why the measured evaporation rate decreased with increasing glycerin concentration. These findings can be applied to demonstrate the moisture-retention capacity of a humectant in cosmetic products through different measuring methods.
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