Synthesis and characterization of temperature-sensitive hydrogels

A series of fire-resistant, temperature-sensitive hydrogels were synthesized via free radical polymerization using N-isopropylacrylamide as a temperature-sensitive monomer, N,N'-methylenebisacrylamide as a cross-linker, ammonium persulfate (APS) as an initiator, and other raw materials including acrylic acid, 2-acrylamido-2-methyl propane sulfonic acid (AMPS), and attapulgite clay (APT). The structures and properties of superabsorbent hydrogels were studied using different analytical tools such as Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA)/differential scanning calorimetry. The effects of the monomer, cross-linker, and other reactants (AMPS and APT) on the water absorption ability of the hydrogels were analyzed; moreover, the effect of valence of metal ions was also examined. SEM images revealed the surface of the hydrogels as uneven and corrugated. The surface toughness increased with increasing APT. The addition of APT and AMPS increased the thermal resistance of the hydrogels but decreased the temperature sensitivity. Furthermore, the swelling ratio of the hydrogels decreased with the increase in salt solution concentration and valency of metal cation present in the salt solutions.