Abstract
Superabsorbent polymers (SAPs) are used in agriculture and environmental engineering to increase soil water retention. Under such conditions, the swelling pressure of the SAP in soil affects water absorption by SAP, and soil structure. The paper presents the results of swelling pressure of three cross-linked copolymers of acrylamide and potassium acrylate mixed at the ratios of 0.3%, 0.5% and 1.0% with coarse sand and loamy sand. The highest values of swelling pressure were obtained for the 1% proportion, for coarse sand (79.53 kPa) and loamy sand (78.23 kPa). The time required to reach 90% of swelling pressure for each type of SAP differs. Samples of coarse sand mixed with SAP K2 in all concentrations reached 90% of total swelling pressure in 100 min, while the loamy sand mixtures needed only about 60 min. The results were the basis for developing a model for swelling pressure of the superabsorbent and soil mixtures, which is a fully stochastic model. The conducted research demonstrated that the course of pressure increase depends on the available pore capacity and the grain size distribution of SAPs. The obtained results and the proposed model may be applied everywhere where mixtures of SAPs and soils are used to improve plant vegetation conditions.
Highlights
Water scarcity is the main factor limiting plant survival in many regions [1,2]
The grain size distribution both of superabsorbent polymer (SAP) and of the tested soils was analysed in order to determine the correct methods for describing the swelling pressure of superabsorbents in a porous medium
The results demonstrate that the percentage of SAP in the mixture has a noticeable influence on the increase in swelling pressure of SAP-soil mixtures
Summary
Water scarcity is the main factor limiting plant survival in many regions [1,2]. The amount and quality of plant growth depends, besides the total water amount and the water use efficiency of a crop, on the relation between the water application strategy and the water holding capacity of the soil [3,4].the significant development of a great variety of soil amendments and smart water systems cannot be surprising [5]. Crystalline swelling of clay minerals is mainly associated with unsaturated conditions, where water potential is controlled by partial vapor pressure, but it may occur under saturated conditions, where the liquid water potential is controlled by high osmotic suction [9]. Another group of recently developed soil amendments are mineral composite superabsorbents that incorporate the above mentioned mineral powders to polymer structure, which, in some cases, may reduce manufacturing costs, and enhance the properties (e.g., water absorbency, gel strength, and mechanical and thermal stability) of superabsorbents (SAPs) [10,11]. SAPs are one type of the maturely developed chemical water-saving
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