Superabsorbent carboxymethyl cellulose-based hydrogel fabricated by liquid-metal-induced double crosslinking polymerisation

Herein, we introduced a liquid-metal/polymerisable deep eutectic solvent (LM/PDES) system to the carboxymethyl cellulose (CMC) and acrylic acid solution to prepare a double-cross-linked CMC-polyacrylic acid (PAA)-LM/PDES superabsorbent hydrogel via graft crosslinking polymerisation for 5 min. FTIR and XRD provided evidence for the coordinate crosslinking between Ga3+ and carboxy groups in the CMC-PAA-LM/PDES gel structure and chemical crosslinking between CMC and PAA components. The pore size of the obtained hydrogels gradually decreases with the increase of LM-AA/PDES content. The rigid CMC polysaccharide chains increased the distance between the ionic groups on the flexible PAA molecular chains, resulting in high osmotic pressure. In addition, the synergistic effects of hydrophilic groups, electrostatic repulsion, macroporous structures and double crosslinking on the CMC and PAA structures provided a driving force and space for the gel to absorb electrolyte containing liquid. The absorption capacity of the CMC-PAA-LM/PDES gel for physiological saline reached 97 g/g, which exceeded that of a single cross-linked CMC-PAA gel and a reported superabsorbent material (71 g/g). This work solved the problem of long heating times and insufficient mechanical properties for the preparation of superabsorbent gels, providing a theoretical reference for improving the absorption capacity of superabsorbent materials for electrolyte-containing aqueous solutions.

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.