Polyurethane Aerogels Based on Cyclodextrins: High-Capacity Desiccants Regenerated at Room Temperature by Reducing the Relative Humidity of the Environment

Abstract

Polyurethane aerogels were prepared from a rigid aromatic triisocyanate (tris­(4-isocyanatophenyl)­methane) and cage-shaped α- and β-cyclodextrins as rigid polyols. Gelation was carried out in DMF using dibutyltin dilaurate as catalyst. Wet-gels were dried to aerogels (abbreviated as α- or β-CDPU-xx) with supercritical fluid CO2. “xx” stands for the percent weight of the two monomers in the sol and was varied at two levels for each cyclodextrin: 2.5% and 15%. All aerogels were characterized with solid-state 13C and 15N NMR, CHN analysis, FTIR, XPS, SEM, and gas (N2 and CO2) sorption porosimetry. α- and β-CDPU-xx aerogels were investigated as desiccants at room temperature. All materials had relatively higher capacities for water adsorption from high-humidity environments (99%) than typical commercial desiccants like silica or Drierite. However, α-CDPU-2.5 aerogels did stand out with a water uptake capacity reaching 1 g of H2O per gram of material. Most importantly though, adsorbed water could be released quantitatively without heating, by just reducing the relative humidity of the environment to 10%. All α- and β-CDPU-xx aerogel samples were cycled between humid and dry environments 10 times. Their unusual behavior was traced to filling smaller mesopores with water and was attributed to a delicate balance of enthalpic (H-bonding) and entropic factors, whereas the latter are a function of pore sizes.

Transparent Polyisocyanurate-Polyurethane-Based Aerogels: Key Aspects on the Synthesis and Their Porous Structures

“…RESULTS AND DISCUSSION Aerogels were fabricated through a sol−gel process, as detailed in Figure 2a. The Fourier transform infrared (FT-IR) spectra of the final aerogels display the characteristic IR peaks for polyurethane and polyisocyanurate (Figure S3): a broad absorption band in the 3600−3200 cm −1 region assigned to N−H stretching, 42 the urethane and urea carbonyl stretching absorptions at 1709 and 1597 cm −1 , respectively, the N−H bending coupled to the C−N stretching is detected at ca. 1513 cm −1 , the isocyanurate carbon−nitrogen stretching is present at 1412 cm −1 , 43 and the C−N stretch can be observed at ca.…”

Review on Polymer Materials for Solid Desiccant Cooling System

“…In addition, Parwani and colleagues developed polyurethane aerogels by combination of cyclodextrins as rigid polyols and a rigid aromatic triisocyanate. [ 214 ] During the gelation process, dibutyltin dilaurate was chosen as a catalyst and tested under the condition of room temperature. They concluded that the samples exhibited stronger abilities in moisture sorption from humid environments (RH level 99%) than traditional desiccants.…”

Polyelectrolyte Complexes as Desiccants: Thirsty Saloplastics

“…Solid desiccants , may be preferred over liquid desiccants − since they are non-corrosive, have lower maintenance costs, larger surface area, and offer flexible applications . Silica has been employed for drying in many applications .…”