Rheology of poly(sodium acrylate) hydrogels during cross-linking with and without cellulose microfibrils

The rheology of poly(sodium acrylate) hydrogel cross-linked with N, N′ -methylene (bisacrylamide), during gelation is studied. The validity of the Winter-Chambon criterion is examined for gelation. Cellulose microfibrils (CMF) of an aspect ratio ranging from 20 to 100 are used as fillers. The effect of filler CMF (0-1 wt %) on the rheological properties during gelation is also investigated. The WC criterion is satisfied and the gel time increased with an increase in the filler content. This suggests the presence of a self-similar structure at the gel point. The storage (G′) and the loss (G″) moduli crossover is observed in the case of unfilled system. Whereas no crossover is observed when the filler is incorporated and from the start of the reaction, G′ is always greater than G″. With the incorporation of the filler, there is a plateau initially in G′ and G″. This is attributed to the physical network of fibrils in the sample mixture. Scaling behavior of rheological properties and fractal dimensions near the gel point are also examined. © 2009 The Society of Rheology.