Saturday, 15 July 2006
137-25

Cyclic Swelling Behavior of Superabsorbent Polymers in Soil Porous Media.

Soheila Ebrahimi1, Mehdi Homaee1, and Babak Ebrahimi2. (1) Tarbiat Modaress Univ, Dept of Soil Science, Tehran, 14155-4838, Iran, (2) IUST, Tehran, Iran

Both arid and semi-arid regions, that cover most parts of the world, suffer not only from lack of precipitation but also from its unsuitable distribution. Agricultural sector consumes major part of the fresh water resources among other sectors. Thus, it is important to increase Water Use Efficiency (WUE) and practical ways to maintain soil water for crop production. The superabsorbent polymers are indeed water containers that absorb and retain large quantities of water when applied into the soil. These materials have the property of releasing the absorbed water, allowing plant to consume enough water at any growth stage. The objectives of this study were to investigate the water uptake model for TA-100 and TA-200 superabsorbent polymers, the cyclic swelling behavior of superabsorbet polymers in soil porous media and to evaluate the polymer's water uptake ability under repeated wetting and drying cycles. Consequently, the amounts of water uptake by TA-100 and TA-200 polymers were recorded at different times. The quantity of absorbed water could be expressed as water taken up in varying lengths of time or as a cumulative amount. The obtained results indicated that water uptake by superabsorbent polymers caused a considerable deformation on polymer's chain, causing mechanical stresses in their configuration which can potentially improve their water transport mechanism. Analyses of the obtained data clearly indicated that the initial stage of diffusion process was well described by the Fick's second law. In order to investigate the cyclic swelling behavior of superabsorbet polymers, two polymers, TA-100 and TA-200, were applied in a loamy and sandy soil. The treatments were consisted of 0, 0.25, 0.5, 0.75 and 1 gr of both polymers per each kg of dry-weighted soil in 3 replicates. The water holding capacity for each treatment at 0, 100, 300, 500, 1000, 3000, 5000 and 15000 kPa, was measured. The Water Retention Curves (WRC) were obtained for each soil sample. The samples were then oven-dried and rewetted for 5 consequent times and the WRCs were again obtained. The results indicated that by applying more polymers in the soils, the water content at any soil water pressure head was increased. However, this influence was declined for next 4 drying-wetting cycles. The most dominant influence of the superabsorbent polymers on water holding at each drying-wetting cycle was appeared on lower soil water pressure heads (0-5000 kPa). The comparison between TA-100 and TA-200 polymers indicated that not only TA-200 had larger water holding capacity, but also appeared to absorb more water than TA-100 during the next 4 cyclic periods. The parametric analysis of the retention curves were indicated that Θs و n and Θr parameters were increased by applying more polymers in all treatments. However, the magnitude of Θr variations was not considerable. It was also observed that the α parameter was decreased in sandy soil and increased in loamy soil by applying any type of superabsorbent.

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