1. Introduction




In the production process of pesticide preparations, the production of foam not only affects product quality, but also may reduce production efficiency and even damage equipment. Therefore, the reasonable selection and use of defoamer is crucial to ensure the stability of pesticide preparations and the smoothness of production. Based on the action mechanism of defoamer, the application of defoamer in the production of pesticide preparation was discussed in this paper.


2. Foam problem in the production of pesticide preparations




Pesticide preparations (such as suspension agent, cream, water agent, etc.) are easy to form foam during production and use due to stirring, shearing, pumping and other operations. These foams are mainly caused by surfactants, thickeners, dispersants and other auxiliaries, which affect the fluidity, dispersion and uniformity of the drug effect. Therefore, it is necessary to add appropriate defoamer to destroy the stability of the foam and reduce the formation and accumulation of the foam.




3. Action mechanism of defoamer




The function of defoamer is essentially to offset the foam stabilization effect of the foam aid material, so as to burst the foam or reduce the formation of the foam. According to the foam stabilization mechanism, the action mechanism of defoamer mainly includes the following:




3.1 Reduce local surface tension, resulting in bubble rupture




When the defoamer diffuses to the surface of the bubble film, it will reduce the surface tension there, forming a local uneven surface tension difference. This inhomogeneity causes the membrane to be subjected to strong traction and eventually rupture. For example, silicone defoamer has a low solubility in water systems and can rapidly expand to the surface of the foam film, thereby reducing local surface tension and accelerating foam rupture.




3.2 Damage the elasticity of the bubble film and weaken the stability of the foam




The stability of the membrane mainly depends on the elastic membrane formed by the surfactant. When the membrane is thinned by external forces, the surfactant molecules quickly rearrange and restore the integrity of the membrane. Defoamer can interfere with this process, reducing the elasticity of the bubble film, resulting in the foam bursting. For example, polyether defoamer can interfere with the arrangement of surfactants and make it difficult for the bubble film to recover, thus playing a defoamer role.


3.3 Promote liquid film drainage, so that the bubble burst quickly




The stability of foam is closely related to the thickness of foam film. Thicker membranes have stronger self-healing ability, while thinner membranes are prone to rupture. Defoamer can speed up the process of liquid discharge of the bubble film, make it thin quickly, and eventually lead to the bubble bursting. For example, a defoamer containing hydrophobic particles, such as hydrophobic silica, can reduce the life of the foam by changing the surface tension of the foam membrane and increasing the rate of liquid discharge.




3.4 Puncture of hydrophobic solid particles




Hydrophobic solid particles (such as hydrophobic white carbon black, hydrophobic silica) can be embedded in the bubble membrane, causing its surface tension to change, thus accelerating the foam rupture. The presence of these particles can enhance the defoaming effect, so many silicone defoaming agents will add hydrophobic solid particles to improve the defoaming efficiency.




3.5 Foam stability is reduced by solubilization




Some low molecular weight substances (such as octanol, ethanol, propanol) can increase the solubility of the foaming surfactant, reducing its effective concentration, thus weakening the stability of the foam. For example, adding an appropriate amount of alcohol to the silicone defoamer can play an auxiliary role in defoaming.




3.6 The double electric layer of surfactant is destroyed by electrolyte action




In some systems, the stability of the foam depends on the repulsion of the double electric layer formed by the surfactant. The addition of electrolytes (such as inorganic salts) can destroy this double electric layer, making the foam less stable. For example, in pesticide preparations, adding an appropriate amount of salt can enhance the defoaming effect.




4. Application of defoamer in the production of pesticide preparations




4.1 Application in suspension agent




Suspensions usually contain high concentrations of surfactants and dispersants and are prone to foaming during grinding and stirring. The use of defoamer can prevent foam from affecting suspension stability and improve production efficiency. The commonly used defoamer includes silicone, polyether and its compound defoamer.




4.2 Application in water agent




The main component of the water agent is water-soluble pesticide. Due to the existence of surfactant, it is easy to produce foam in the preparation and spraying process. Appropriate addition of low molecular alcohol or polyether defoamer can effectively reduce the foam and improve the uniformity of the drug effect.




4.3 Application in cream




The cream is usually composed of solvents, emulsifiers, and pesticide active ingredients and is prone to foaming when diluted for use. Since the emulsion system is an oil phase, the selection of defoamer needs to consider the compatibility with the emulsifier, and generally adopts silicone defoamer with strong hydrophobicity to prevent emulsification instability.




4.4 Application in microemulsions and water-dispersed granules




Both microemulsions and water dispersible granules contain a certain amount of surfactant, which is easy to bubble during production and use. For this kind of system, silicone-polyether compound defoamer can be used to balance the defoamer efficiency and system stability.




Defoamer plays an important role in the production of pesticide preparations, and its mechanism involves reducing surface tension, destroying membrane elasticity, accelerating liquid discharge, punctured membrane by solid particles, solubilization and electrolyte destruction of double electric layer. According to different pesticide preparation types and production needs, reasonable selection of suitable defoamer can effectively control foam, improve production efficiency and product quality. In the future development of pesticide preparations, environmental protection, high efficiency, low impact defoamer will become the focus of research.