Preparation and characterization of polyacrylamide-modified kaolinite containing poly [acrylic acid-co-methylene bisacrylamide] nanocomposite hydrogels

Novel nanocomposite hydrogel structures based on cross-linked poly(acrylic acid) (PAA) and kaolinite (Kaol), modified with different loadings of polyacrylamide (PAAm), were prepared by inverse dispersion polymerization. Ceric ammonium nitrate as an initiator in the presence of nitric acid was used to graft PAAm from the Kaol surface. The surface-modified Kaol showed enhanced interactions between the filler and the PAA matrix, through interactions between amino (-NH2) from PAAm and carboxylic groups (-COOH) from PAA. The XRD and TEM measurements confirmed the exfoliated nanocomposites with the Kaol filler. The swelling degree (SD) of the swollen hydrogel nanocomposite was increased following the addition of polyacrylamide-modified Kaol particles into the hydrogel structures. Rheological characterization showed that an increase in the storage modulus (G') could be a consequence of a good dispersion of Kaol particles in the polyacrylic acid matrix, thereby leading to enhanced interactions and furthermore to improved mechanical properties of the final hydrogels.