2.2. Gravimetric Moisture Sorption/Desorption Analysis

Automated moisture (de)sorption studies were performed with the automatic multisample gravimetric moisture sorption analyser SPSX-10 μ (ProUmid, Ulm, D). The moisture sorption analyzer was calibrated with saturated salt solutions according to the suppliers’ recommendations. Approximately 80–300 mg of sample was used for each analysis.

The first measurement cycle was started at 40% with a desorption cycle (decreasing humidity) to 0%, followed by a sorption (increasing humidity) to 95% RH, a desorption cycle to 0% RH, and a final sorption step to 40% (one step). RH changes were set to 5%. The equilibrium conditions for each step were set to a mass constancy of ±0.015% over 40 min and a maximum time limit of 48 h.

The second measurement started at 43% RH with an initial stepwise desorption to 0%, followed by a sorption cycle back to 43%, with RH changes set to 2% (except for the steps 43% ↔ 40% RH).

The third measurement started at 40% RH and covered the RH range 40 ↔ 95% in 5% steps and the RH range 40 ↔ 0% in 0.5% steps. The equilibrium conditions for each step (second and third measurement) were set to a mass constancy of ±0.001% over 60 min and a maximum time limit of 48 h.

In addition, manual water desorption studies were performed for HyC and HyF over a desiccant (P₂O₅) at 25 °C. The loss of water as a function of time was determined gravimetrically⁵⁵ with a below-weighting balance (AT 250 semimicro balance, Mettler Instruments AG, Greifensee, CH). The sample mass used in each of these studies was about 200 mg.