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AAPS PharmSciTech. 2001 December; 2(4): 73–79.
Published online 2015 February 19. doi:  10.1007/BF02830568
PMCID: PMC2784843

An examination of the moisture sorption characteristics of commercial magnesium stearate


The objective of this study was to characterize the moisture sorption of magnesium stearate and the morphological changes, if any, resulting from moisture sorption. Six samples of commercial magnesium stearate USP were examined. Moisture sorption isotherms were obtained at 25°C and 5% to 98% relative humidity (RH) using a moisture balance. Changes in crystal form resulting from moisture sorption were determined by x-ray diffraction. There were differences in the shape of the isotherm, reversibility of moisture uptake, and shape of the hysteresis loop in the isotherms of crystalline and amorphous magnesium stearates. The isotherm of crystalline magnesium stearate was almost parallel to the pressure axis until and RH of ~80%. The isotherm of the amorphous sample was characterized by continuous uptake of water over the entire range of RH. Exposure of amorphous magnesium stearate to RH greater than 70% resulted in the formation of the trihydrate. The trihydrate was converted into the anhydrous form when heated to a temperature of 100°C to 105°C. The trihydrate could be generated by exposing the anhydrate to RH higher than 70%.

KeyWords: Moisture sorption, magnesium stearate hydrates, crystalline, amorphous magnesium stearate

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
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