The effects of co-formulating amorphous maltodextrins (MDs) and sodium chloride (NaCl), a deliquescent crystalline solid, on moisture sorption, deliquescence point (RH0), and glass transition temperature (Tg) behaviours were investigated. Moisture sorption profiles of binary NaCl:MD mixtures and individual ingredients were generated using controlled relative humidity (RH) desiccators at temperatures from 22 to 50°C and by dynamic vapour sorption (DVS) and dynamic dewpoint sorption (DDS) techniques. Close proximity of MD and NaCl induced synergistic moisture uptake in binary mixtures above a threshold RH, resulting in significantly lower Tgs in binary mixtures compared to individual MDs. The RH0 of NaCl was also lower in the blends. Mixing amorphous MD with crystalline NaCl resulted in synergistic moisture sorption and reduced both Tg and RH0, thus blends were more sensitive to environmental moisture than the individual solids. This has implications for quality control of many formulated powder products.
Keywords: Crystalline and amorphous; Deliquescence point; Dynamic vapour sorption; Glass transition temperature.
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