Water Absorption Kinetics by Super-absorbent Polymers

Document Type : Complete scientific research article


1 Dept. of Soil Science, Gorgan University of Agricultural Sciences and Natural Resources, Iran,

2 Dept. of Soil Science, Tarbiat modares University, Tehran, Iran,

3 Dept. of Chemical Engineering, Tarbiat modares University, Tehran, Iran


Background and objectives: The increase of irrigation efficiency is a technique applied to water conservation; therefore, appropriate and productive management and the application of efficient methods in order to maintain enough water in the soil for optimum utilization of scarce water resources is necessary in the long run. The use of super-absorbent polymers offers effective ways of saving water in agriculture. However, before selecting a suitable polymer, determining of an appropriate model is essential.
Materials and Methods: In this study, the water absorption model was evaluated by two super-absorbent polymers from polyacrylamide family, abbreviated as T-A200 and T-A100. The experiment was carried out with four replicates and water absorption was recorded by the polymers in different times until reaching the equilibrium swelling (stable inflation), as instantaneous and cumulative. After testing the free swelling, the absorption kinetics of fluid (the changes in the absorption of water by the gel time) was determined by immersion in water. After that the result was presented by a graph that depicted the changes in the ratio of absorbed solvent in time to this solvent in equilibrium in time. Also, the trend of solvent absorption by the two polymers in time measured. To determine the mechanism of penetration, the mentioned model used and the values of n and k were calculated.
Results: The results showed that the fluid absorption in heterogeneous environments such as gels was associated with significant deformation. The graph shows that in all cases n was less than 5.0, and therefore the mechanism of transfer of the solvent into the polymer network follows the Fick's law.
Conclusion: the appropriate super-absorbent polymers in agriculture must be able to absorb maximum amount of water at the minimum time; therefore, doing so will prevent from the loss of rainfall or irrigation water applied. To prove it, the model should follow the Fick diffusion which penetration rate is lower than the speed of molecular relaxation, and only diffusion phenomena is effective through the transfer of ground-penetrating, so, molecular relaxation phenomenon does not affect on the transfer of ground-penetrating. Consequently, after any deformation or swelling, the polymers quickly reached a new balance and stresses will quickly vanish; therefore, it does not have any effect on the speed of penetrating component. In this study, the penetration of the fluid into the polymer followed the Fick model. Hence, this model would certainly be recommended to periodic swelling ability in agricultural purposes.


1.Ebrahimi, S., Homaee, M., and Vasheghani Farahani, E. 2008. Cyclic Swelling of superabsorbent polymers in soil porous media. J. Agric. Engin. Res. 8: 4. 1-18. (In Persian)
2.Eubeler, J.P., Bernhard, M., and Knepper, T.P. 2010. Environmental biodegradation of synthetic polymers. 2. Biodegradation of Different Polymer Groups. Trends in Analytical Chemistry, 29: 1. 84-98.
3.Frisch, H.L. 1980. Sorption and transport in glassy polymers - A review. polymer engineering science Polym. Eng. Sci. 20: 2-13.
4.Kazanskii, K.S., and Dubrouski, S.A. 1992. Chemistry and physics of agricultural hydrogels. J. Adv. Polym. Sci. 101: 97-133.
5.Kim, S.J., Shin, S.R., Lee, Y.M., and Kim, S.I. 2003. Swelling characterizations of Chitosan and Polyacrylonitrile semi-interpenetrating polymer network hydrogels. J. Appl. Polym. Sci. 87: 2011-2015.
6.Michigan, J. 2006. Hydrogel polymer effects on available water capacity and percolation of sandy soils at Al – Hassa, Saudi Arabia. CSBE/SCGAB Annual conference.
7.Naderi, F. 1996. Evaluation of Hydrogel swelling behaviors in porous media. MS. Thesis in Chemical Engineering, Faculty of Engineering, TarbiatModaresUniversity. 130p. (In Persian)
8.Nofziger, D.L., and Wu, J. 2003. Diffusion of solutes in soil. Department of Plant and Soil Science, OklahomaUniversityPress, U.S.A.
9.Rockett, T.J., and Rose, V. 2003. Water diffution in hull materials. Department of Chemical Engineering., Rhode Island University Press, Kingston.
10.The Ministry of Agriculture. 1999. Vice President of Planning and Budget. Ministry of Agriculture, Agriculture in a glance. 91p. (In Persian)
11.Vashegani-Farahani, E. 1990. Swelling and exclusion behavior of hydrogels. Ph.D. Thesis, cGillUniversity, Montreal, Canada.
12.Xiahua, Q., Mingzhu, L., Zhenbin, C., and Fen, Z. 2008. Study on the swelling kinetics of superabsorbent using open, circuit potential measurement. Euro. Polym. J. 44: 743-754.