The Behavior of Water Absorption and Dehydration of Organic Materials

Application Note B-TA1003

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.

 

α-シクロデキストリンの吸水・脱水挙動

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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