Effect of Soluble Salts and Their Concentrations on Water Absorption of Polyacrylic Acid Sodium Salt

摘要

This research was conducted to determine the amount of water absorbed by polyacrylic acid sodium salt (PASS), effect of salts on inhibition of hydration of PASS, and the hydrogel effects on changes of nutrient concentrations in the external solution.Absorption of deionized water by PASS reached a maximum of 210 mL.g~(-1). Monovalent soluble salts, KH_2PO_4, KNO_3, and (NH_4)_2SO_4, reduced amount of water absorbed by PASS, but the degree in inhibition of absorption was similar in three kinds of salts. Twenty milliequivalents per liter of Ca~(2+) or Mg~(2+) reduced water absorption of PASS by 4%, as compared to those of deionized water. Solution absorption was consistently lower in the presence of divalent cations than in the presence of the monovalent cations. However, the absorption was unaffected by the uncharged salt such as urea at all concentrations tested. The K~+ and NH_4~+ concentrations of the solution remaining after absorption by PASS decreased sharply and no NH_4~+ was analysed at 10 minutes after soaking of the hydrogel. The Na~+ concentration in external solution of PASS increased during gel hydration reaching 610 mg.L~(_1) . The concentrations of NO_3~-, H_2PO_4~- and SO_4~2 in external solution of PASS did not fluctuate during experiment.