Water Vapor Adsorption Behavior of Thermosensitive Polymers for Desiccant Humidity Control Systems

Desiccant humidity control systems have been garnering considerable attention in the attempt to achieve highly efficient utilization of low-temperature heat exhausted from various industries at temperatures less than 373 K. We have focused on thermosensitive polymers as new desiccants because a large amount of dehumidified water would be expected in the system because of their thermosensitivity. Our previous study focused on the water adsorption behavior of poly(N-isopropylacrylamide) (poly(NIPA)), which has a low critical solution temperature (LCST) of 306 K. In this study, poly(N-isopropylmethacrylamide) (poly(NIPMA)) and poly(2-(dimethylamino)ethyl methacrylate) (poly(DMAEMA)) cross-linked with N,N'- methylenebisacrylamide (MBAA) were investigated. These polymers are known to exhibit thermosensitivity in the temperature range of 313-319 K in water, which is a higher LCST than that of poly(NIPA). Poly(NIPMA) adsorbed water vapor linearly with increasing relative humidity. It was also observed that poly(NIPMA) prepared at MBAA concentrations of 200 mol/m(3) exhibited a thermosensitivity in the temperature range of 303-313 K in water vapor adsorption. Meanwhile, poly(DMAEMA) adsorbed little water vapor up to a relative humidity (RH) of 40%; however, it exponentially adsorbed water at RH levels higher than 40%. From the estimation results of effective water adsorptivity, we found that poly(DMAEMA) is applicable in desiccant humidity control systems when the dehumidification process is performed at high RH.