Effect of Neutral Salt and pH on the Swelling of Cellulosic Super Water-absorbent.

Abstract

To clarify the swelling behavior of a cellulose-partially hydrolyzed polyacrylamide graft copolymer as a super water-absorbent, the effects of swelling conditions such as the concentration of neutral salt and pH value on the swelling of the graft copolymer were studied. The absorbency of the copolymer, the porous structure of the hydrogel of the copolymer, and the dynamic viscoelasticity of the hydrogel were examined. The absorbency was decreased steeply by the addition of sodium chloride. It depended remarkably on the solution pH and had a maximum value at about pH 7. Examination using the solute exclusion technique revealed that the distribution of pore width in the graft copolymer swollen in water differed from those in aqueous sodium chloride solutions and in an acidic or alkaline solution. When the concentration of sodium chloride increased or the pH was reduced or increased from pH 7, the cumulative pore volume up to 560 A in pore width decreased. Their relative value, however, increased accompanying the increase in the values of dynamic viscoelasticity of the hydrogel.