Superabsorbent hydrogel composite made of cellulose nanofibrils and chitosan-graft-poly(acrylic acid)

Superabsorbent hydrogel composites based on cellulose nanofibrils and chitosan-graft-poly(acrylic acid) copolymer were developed in this work. The FTIR data showed that the copolymerization and the composite formation reaction were successfully performed. In addition, the XRD pattern indicated that the nanofibrils crystallinity was as high as 90%. A 2(4-1) fractional factorial design was employed to evaluate the effect of acrylic acid/chitosan molar ratio, crosslinker, initiator, and filler in the swelling capacity of hydrogel composites. By the analysis of variance (ANOVA), including F-test and P-values, it was found that the crosslinker and filler correspond to 40% and 30% of the evaluated response, respectively. The addition of nanofibrils provided faster equilibrium conditions as well as improved the swelling capacity in ca. 100 units, from 381 to 486. SEM images showed that the addition of nanofibrils into the hydrogel matrix increased the averaged-dimension of porous. Finally, the composites showed responsive behavior in relation to pH and salt solution. Such characteristics make these smart materials suitable for several technological applications. (C) 2011 Elsevier Ltd. All rights reserved.