Superabsorbent nanocomposite hydrogels based on intercalation of chitosan into activated bentonite

Abstract

Superabsorbent polymers, composed of acrylamide (Am) and 2-acrylamido-2-methyl-1-propane sulfonic acid, were prepared by the solution crosslinking polymerization technique. The effect of the ionic monomer content was correlated with the equilibrium swelling capacity. The swelling capacity was augmented up to 94 g/g by increasing the concentration of the ionic monomer. Intercalation of bentonite clay, by chitosan solution, was performed by two techniques, namely, microwave irradiation and heating. The basal spacing of bentonite increased from 1.21 to 1.31 nm for the former and to 1.4 nm for the latter. Specific interaction of bentonite with –OH group of chitosan through hydrogen bonding was estimated by FT-IR. Also, TEM showed a layered morphology due to the penetration of chitosan chains into bentonite silicate layers. Different amount of the intercalated clay was dispersed in the aforementioned monomers aiming at preparing superabsorbent composites. The clay showed an exfoliated structure in the polymer matrix while the composite was porous, with a three-dimensional interconnected microstructure as proved by SEM. The prepared composites had a higher absorption capacity up to 180 g/g and a better thermal stability than the corresponding hydrogel.