Gamma radiation synthesis of a humidity sensor hydrogel based on superabsorbent of poly sodium acrylate and poly <i>N</i> -isopropylacrylamide copolymer loaded with CaCl ₂ and charcoal

The primary objective of this research is to fabricate highly hydrophilic composite hydrogels to be used as a humidity sensor. A series of interpenetrating network copolymer hydrogels based on sodium acrylate (SA) and N -isopropylacrylamide (NIPAAm) monomers has been synthesized under the effect of gamma irradiation. The hydrogels were loaded with calcium chloride and charcoal as fillers. For comparison, hydrogels based on pure monomers were also synthesized. The pure hydrogels and composite hydrogels were characterized by different analytical methods such as gel content analysis, FT-IR spectra, swellability in water, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water vapor uptake and humidity absorption. The results obtained indicated that the copolymer and composite hydrogels with CaCl 2 and charcoal Showed significant improvement in swellability in water, thermal stability and water vapour uptake and humidity absorption. The findings revealed also that the gel fraction is largely dependent on the irradiation dose and hydrogel composition. The addition of CaCl 2 and charcoal in the composite hydrogels strongly enhances the humidity absorption capacity of the dried gel and increases the humidity absorption capability in comparison to the hydrogels based on pure monomers.