Superabsorbent polymeric materials III. Effect of initial total monomer concentration on the swelling behavior of crosslinked poly(sodium acrylate) in aqueous salt solution

Abstract

A series of xerogels based on sodium acrylate (SA) and N,N′-methylene-bisacrylamide (NMBA) were prepared by inverse suspension polymerization. The water absorbency or swelling behaviors for these hydrogels in water or various saline solutions was investigated. Experimental results indicate that the absorbency of poly(SA) in deionized water increases with decrease in the initial total monomer concentration. Results obtained from this study show that the water absorbency, respectively, exhibited a value of 992 g H2O/g sample and 106 g H2O/g sample in deionized water and a 0.9 wt % NaCl solution at an initial total monomer concentration of 3.03M. The absorbency in the chloride salt solutions decreases with increase in the ionic strength of the salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Co2+ > Ni2+ > Cu2+ for the higher ionic strength of 6.25 × 10−4 to 2.0 × 10−3M, and Co2+, Ni2+, and Cu2+ approximately have the same swelling amount for the lower ionic strength of < 6.25 × 10−4M. The influence of monovalent, divalent, and trivalent anions with a common cationic ion (Na+) on the water absorbency shows the tendency of monovalent < divalent < trivalent anions for the same ionic strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2371–2380, 1997