Poly(sodium 4-styrene sulfonate) and poly(2-acrylamidoglycolic acid) nanocomposite hydrogels: montmorillonite effect on water absorption,thermal, and rheological properties

A systematic study of water absorbency, thermal, and rheological properties was performed on nanocomposite hydrogels of poly(sodium 4-styrene sulfonate) (PSSNa) and poly(2-acrylamide glycolic acid) (PAAG). Montmorillonite was used as clay filler and was previously modified to hydrogel synthesis by addition of (3-acrylamide propyl)trimethylammonium chloride. Syntheses were carried out by in situ radical polymerization, using N,N-methylen-bis-acrylamide as crosslinker reagent. Nanocomposites showed an exfoliated morphology, confirmed by transmission electron microscopy and X-ray diffraction. The water absorption capacity (WAC) of unloaded PSSNa hydrogel was three times higher than for PAAG; due to clay addition, absorption capacity increased for PSSNa nanocomposites and decreased for PAAG. Finally, rheological properties of nanocomposite hydrogels were studied by both dynamic oscillatory test and shear creep analysis. Results showed improvements on mechanical properties, such as yield point, elastic recovery, and storage modulus as consequence of montmorillonite addition.