Effect of aluminum sulfate, Al2(SO4)3, on dispersion state of sodium carboxymethylcellulose, NaCMC, in aqueous solution was investigated by rheological measurements and X-ray photoelectron spectroscopy (XPS). Rheological properties of NaCMC aqueous solutions containing Al2(SO4)3 were investigated using a cone-plate type rheometer. When NaCMC concentration was 0.5 wt %, shear stress of the solution slightly decreased with increasing concentration of Al2(SO4)3. On the other hand, when NaCMC concentration was 5 wt %, the shear stress increased with increasing Al2(SO4)3 concentration. In this case, both dynamic storage and loss moduli also increased. These results suggest that the addition of Al2(SO4)3 increased crosslinking density and caused heterogeneous aggregation of NaCMC. This was confirmed by the fact that diluted Al2(SO4)3-containing NaCMC solution was separated to microgel-like particle and homogeneous solution. XPS revealed that aluminum ion was concentrated in the microgel-like particle. From these results, dispersion state of NaCMC in aqueous solution containing Al2(SO4)3 was modeled as microgel-like particle containing concentrated aluminum ions are suspended in the network of NaCMC chains.
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