Structure–property correlations for PEG-interpenetrated hybrids of poly(acrylamide-co‑sodium acrylate) reinforced with Laponite, halloysite, sepiolite and montmorillonite

Abstract

This study investigates the impact of different clay types on the properties of clay polymer nanocomposites (CPNs). semi-interpenetrated (semi-IPN) cryogels consisting of poly(acrylamide-co‑sodium acrylate)/poly(ethylene glycol) (PAN/PEG) and various clay minerals such as Laponite, sepiolite, halloysite, and montmorillonite were prepared following “in situ” synthetic protocol. The aim was to determine most effective inorganic component for developing desired elasticity and swelling/shrinking ability. By fixing the concentration of clay minerals embedded in CPNs as 1.50 % (w/v), the effect of inorganic clay type on structural properties was evaluated in terms of polymerization temperature, compressive elasticity, pH and thermo-sensitivity. Clay type had an effect on the thermal stability of semi-IPNs, while sepiolite increased the stability and compressive modulus to a higher extent. Among the four types of semi-IPNs, the water absorbency of montmorillonite-integrated gel was the highest, while that of sepiolite-doped was the lowest. The elastic moduli of semi-IPNs incorporated with same amount of clay is in the order Sepiolite > Halloysite > Laponite > Montmorillonite. Changing pH in the range of 2.1 to 11.2 significantly increased the swelling, while a small variation in pH 6.6 caused a large difference in swelling capacity. For pH-dependent cyclic swelling, the highest swelling-shrinkage response was observed in Laponite-doped cryogels. The swelling of nanocomposites was significantly weakened by the change in ionic strength, while the swelling increased with the incubation temperature, showing good agreement with Fickian diffusion. Among the nanocomposites for cationic methylene blue (MB) dye, Laponite-integrated semi-IPNs exhibited the highest adsorption capacity from aqueous solution with 89.51 mg/g. MB adsorption kinetics followed pseudo-second-order, Freundlich and Redlich–Peterson isotherm models. The findings provide strategic approach for promising material design, supporting the development of potential applications of polyelectrolyte semi-IPN nanocomposite cryogels as biomedical materials.