The Behavior of Water Absorption and Dehydration of Organic Materials
Introduction
Some reagents are hygroscopic, and the adsorbed water can have strong or weak bonding forces. These features can be identified by humidity- and temperature-controlled methods. However, ordinary simultaneous thermal analysis (STA) combined with thermogravimetry and differential thermal analysis cannot conduct humidity-controlled measurements. It is impossible to measure mass changes depending on humidity, such as wet-to-dry or vice versa. However, mass changes of reagents under controlled humidity can be performed by STA with a humidity generator (HUM-1).
Measurements and results
Water adsorption and desorption of α-Cyclodextrin were investigated using STA with HUM-1 by the following processes: 1st heating in dry N₂ (25°C, 2%RH) (process ①, P①), cooling and then holding at 25°C in dry N₂ (P②), increasing humidity from dry to 90%RH at 25°C (P③), decreasing humidity from 90%RH to dry at 25°C (P④), repeating processes ③ and ④ once, and then conducting 2nd heating in dry N₂ (P⑦).
Results of α-cyclodextrin by STA with a HUM are displayed in Figure 1. Two steps of mass losses of 3.5% and 6% associated with dehydration were observed during the process of P①. A mass increase of 1.5% related to water absorption occurred during the process of P②. A mass increase of 11% associated with water absorption was illustrated under experimental conditions of 25°C and 90%RH during the process of P③. This suggests that a mass increase of 12.5% related to water absorption was observed with a rise of humidity from 2%RH to 90%RH at 25°C during the processes of P② and P③. In addition, a mass loss of 6.5% was exhibited with humidity variations at 25°C during the processes of P④, P⑤, and P⑥. These results indicate that the total amount of water absorption was about 12.5% in the processes of P② and P③, in which about 6% of water shown in P⑦ cannot be evaporated under experimental conditions of 2%RH and 25°C. In other words, about 6.5% of water was susceptible to humidity variations during the processes of water absorption and dehydration at 25°C.
Figure 1: The behavior of water absorption and dehydration of α-cyclodextrin
Recommended equipment and software:
- Thermo plus EVO2 TG-DTA8122/HUM-1
- Vullios measurement and analysis software
Related products
STAvesta/HUM
Humidity-controlled STA
The compact humidity generator is connected to the STA (TG-DSC) for measurements under constant relative humidity water vapor atmosphere

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