Application of Anionic Polyacrylamide in the Water-retaining Agent

In agriculture planting, soil improvement, and compound fertilizer production, the main component of water-retaining agent is polyacrylamide. Anionic polyacrylamide with high quality and low price is more suitable for agricultural planting as a water-retaining agent. So why is anionic polyacrylamide more suitable as a water-retaining agent? Does anionic polyacrylamide always serve as a water-retaining agent in all cases? Are there any requirements for the selection of anionic polyacrylamide in water-retaining agents?

Soil water-retaining agents are high-molecular-weight polymers, mainly composed of copolymers of polyacrylic ester and polyacrylamide. The main substance is polyacrylamide, which contains a large amount of specific structured strong water-absorbing groups that can quickly absorb deionized water hundreds of times their own weight and saltwater tens of times or hundreds of times their weight, creating a "small water reservoir" capable of rapidly absorbing, storing, and slowly releasing moisture and nutrients. It presents two states: the net state and the linear state. The mesh soil water-retaining agent belongs to cationic polyacrylamide and is equivalent to a highly water-absorbent resin, which can be used as a farmland water-retaining agent. The linear soil water-retaining agent belongs to anionic or non-ionic polyacrylamide, is used as a soil improver due to its long molecule chain, and plays an important role in controlling and preventing soil erosion.

Principles of the soil water-retaining agent

Water-retaining agents are high-water-absorption organic molecules with carboxylate groups that are highly cross-linked and formed by polymerization, containing strong hydrophilic groups. They have a strong affinity for water due to the osmotic pressure produced by the difference in the concentration of ions and groups in the water solution and the affinity of polymer electrolytes for water. Polyacrylamide water-retaining agents contain a large number of amide and carboxyl hydrophilic groups that can absorb a large amount of water until the concentration difference disappears by the osmotic pressure caused by the difference in the electrolyte ion concentrations within and outside the molecule, and the rubber elasticity of the water-retaining agent controls the satisfactory water absorption. The higher the crosslinking degree of the molecular structure, the stronger the rubber elasticity, and the balance point between rubber elasticity and water absorption is the apparent water absorption ability. Water-retaining agents are different from general resins, which do not exist in monomeric form. They do not burn or explode, are non-toxic and non-corrosive, and are insoluble in water. Natural water is absorbed into the hydrophilic group network structure, forming a water hydrogel after water absorption. The moisture released slowly by the soil moisture evaporation caused by environmental drought and the suction force of plant roots maintains the surrounding soil moisture, which is absorbed and utilized by plant roots.

Of all types of polyacrylamide, anionic polyacrylamide, non-ionic polyacrylamide, and cationic polyacrylamide are suitable for use as water-retaining agents. Compared with water absorption performance, anionic polyacrylamide has the highest water-absorption multiple, water release, and gel strength. Most importantly, the price of anionic polyacrylamide is the lowest among the three types of polyacrylamide.

Anionic polyacrylamide is the preferred water-retaining Agent

When used, loose-textured and highly fluid sandy soil is more suitable for high-molecular-weight polyacrylamide, while compact soil is more suitable for low-molecular-weight polyacrylamide. However, anionic polyacrylamide is not always used in all situations. For example, in some areas with extreme drought and severe sandstorms, cationic polyacrylamide is the most commonly used. This is mainly because cationic polyacrylamide is a high-molecular-weight polymer with a network structure that has a certain water-retention capacity, and its network structure can better prevent wind and sand erosion and reduce soil erosion. It should be noted that when using water-retaining agents in the same area, cationic polyacrylamide and anionic polyacrylamide cannot be used simultaneously, otherwise, a reaction will occur, which will reduce the effectiveness of use.