Effects of agricultural herbicide on water absorption characteristic of super absorbent polymer

The water absorption characteristic of super absorbent polymer (SAP) is one of the most important indices for agriculture drought-resistant measurement. The SAP is easily affected by many soil environmental factors, such as soil particles, organic matter, and nutrients. The herbicide is widely used in agricultural management, thus the water absorption characteristic of SAP can be affected by herbicide leaching into soils. The membrane structure of SAP would be damaged by herbicide molecule, changing the surface microtopography of SAP and reducing water absorption characteristics. In this paper, a SAP frequently used in agriculture was selected as the experimental object, of which solid particle is yellow with diameter 1.0-2.0 mm, the deionized water absorption amount is 100-700 g/g and the 0.9% NaCl solution absorption amount more than 32 g/g. Three common herbicides（Atrazine，Alachlor and Tribenuron-methyl）with three mass concentration（0.5, 1, 2 mg/L）were selected as the influencing factors. Actual water absorbing capacity of SAP in deionized water and different Herbicide solution were tested by the filtration method with 100 mesh sieve. Scanning electron microscope (SEM) analysis was used to obtain the surface microtopography characteristic of SAP, and fractal analysis was used to study quantitative effects of three Herbicideon on its surface microtopography at the swelling equilibrium point. It was observed that the overlapping shape occurred in the surface of dry SAP particle and the porous structure in the surface of SAP hydrogel. Alachlor and Tribenuron-methyl（0.5, 1, 2 mg/L）reduced water absorption amount and single fractal dimension of surface microtopography, but reductions were not obvious because the three-dimensional network of SAP was kept relatively intact. However, Atrazine significantly changed the surface microtopography characteristic of SAP , and the bigger the mass concentration of Atrazine, the smaller the water absorption amount of SAP. The membrane structure was destroyed with the concentration of Atrazine at 2 mg/L. Relative to deionized water, the water absorption amount in Atrazine (2 mg/L) was reduced by 9.64%. Single fractal dimension and multifractal spectrum singularity index span decreased with increasing mass concentration of Atrazine, showing the more uniformity of its surface pores distribution, the smaller complexity of its network structure. This research provides a quantitative analytical method to study effects of the herbicide on water absorption characteristic of SAP by using scanning electron microscope and fractal methods.