Synthesis of self-crosslinking sodium polyacrylate hydrogel and water-absorbing mechanism

Abstract

In this paper, the super-absorbent, self-crosslinking sodium polyacrylate was synthesized by means of reversed-phase suspension polymerization under gamma-ray irradiation and the water-absorbing mechanism of the self-crosslinking hydrogel was revealed. Some physical parameters of such a network were estimated and investigated. The stable suspension polymerization of sodium acrylate was carried out in the presence of a surfactant complex consisting of anionic surfactant dodecylbenzen sulfonic sodium (DSS) and nonionic surfactant Span60 or Span20 with a certain ratio. The dual-electronic structure resulted from such a surfactant complex makes the dispersed monomer solution droplets a stable suspension in organic solvent. The water-sorbability was related to the radiation conditions such as dose, dose rate, and degree of monomer neutralization. Only under high dose and dose rate, some initiated branch side species on the main macromolecular chain can couple each other and cause a self-crosslinking network which may contain a lot of water. The gel dose was about 1.57 kGy (radiation dose unit), and G(X), or G value expressed as crosslinking probability at certain energy of 100 ev, was calculated and found to be 2.46 (1/100 ev). The water-sorbing procedure includes three stages, e.g., sorption on the pore surface, ionization of the fixed charges in the network, and swelling equilibrium. The crosslink chain length in the self-crosslinked sodium polycrylate network, expressed as Mc, can be calculated and related to gel dose.