The extraordinary water absorption capacity of superabsorbent polymers has been under investigation for a long time. However, the mathematical understanding of the swelling mechanism is obscure. In this study, mathematical equations have been established to illustrate the mass-transfer phenomena during the water absorption inside the superabsorbent polymer. Transport phenomena of water from solution to polymeric beads have been demonstrated on the basis of size variation with time. The derived equations in this article are useful to evaluate the mass transfer coefficient of water inside the superabsorbent polymer. The calculated mass transfer coefficient of water without salts is 5.08×10⁻⁶ m/s, and the water concentration inside the ball after 24 hours of expansion is 993.41 kg/m³. A linear variation (slope = -4×10⁻⁸ m/s) in the size of the residual sphere is also observed. The same equations have also been capitalized to compare the water transfer phenomena in the presence of cations and anions. Results show that the presence of ions in the environment restricts the mass transfer of water inside the polymeric bead. This study has the potential to predict the mass transfer coefficient of polymer beads under different experimental conditions using minimum laboratory resources. In addition, this study will help to design different mass transfer-related experiments for researchers.
Nigam et al. (Wed,) studied this question.