Diffusion vapor sorption analysis (DVS)

The sorption isotherm of SAP was determined using Dynamic Vapor Sorption equipment (VTI-SA, TA Instruments, Eschborn, Germany). The polymer powder was placed in the sample holder, which was hung in the thermostatically controlled cabinet where the pre-set relative humidity (RH) was increased from 0 to 90 % in steps of 10 % in a pre-programmed sequence. The mass of polymer was set at 35 mg and the sorption process was run at a constant temperature of 40 °C over the full RH range. The running time, isotherm temperature, target RH, actual RH, and sample weight were recorded throughout the isotherm run (data not shown).