Types of surfactants and their application to pesticides

Surfactants can be used to make pesticide preparations that can not be used directly. As a pesticide additive applied to pesticides, it can not only improve the use effect of pesticides, but also reduce the amount of pesticides, reduce the impact of pesticides on the environment, and bring great benefits to agricultural production. However, since pesticides are a class of special chemicals with strong biological activity, and their control objects, protection objects and environmental conditions are very complex, the surfactant in pesticides must be selected and formulated according to the nature and characteristics of the original drug, but also consider the impact of the surfactant itself on the target organism.

1, solvent increase

Using the micelle action of surfactants, the solubility of the insoluble agent in the solvent is significantly increased, which is solubilization. Surfactants with HLB=15-18 can be used as solubilizers, but only when the concentration of solubilizers is higher than the critical micelle concentration. At this time, the insoluble drug is contained or adsorbed in the rubber by the lipophilic group of the solubilizer, the hydrophilic group of the solubilizer is in water, and the non-polar drug is soluble in water.

2. Dispersant

Dispersants can hinder or prevent the aggregation of solid or liquid particles in the dispersion system, and keep them uniformly dispersed for a long time. The dispersant is adsorbed at the oil-water interface or on the surface of solid particles, forming a charge or steric barrier around the particles, which helps to prevent the re-aggregation of pesticide particles during mixing and storage. Generally used as a dispersant is a polycyclic anionic surfactant, such as alkyl naphthalene sulfonate and naphthalene sulfonate formaldehyde condensation of sodium salt, lignosulfonate, etc. Polymer dispersants (such as sodium polycarboxylate) are particularly important in the preparation of aqueous suspension because of their adsorption properties and their ability to charge dispersed particles and have large spatial barriers.

3. Wetting agent

Most organic synthetic agents are sulfur-based and need to be mixed with water. Water based preparations such as wettable powder, suspension agent, water dispersion granule, etc., need to add wetting agent. The main surfactants used as wetting agents are anionic surfactants (such as fatty alcohol sulfate, dodecyl benzene sulfonate, etc.) and non-ionic types (such as Perigat, Agromilk 100#, Agromilk 600#, Tween, sorbitol polyoxyether, etc.). Some natural products such as lignosulfonate, tea, and saponin are also good wetting agents. Due to the role of wetting agent, the dispersion of the drug can be increased, the stability of the preparation can be increased, and it is also conducive to the release, absorption and enhancement of the drug effect.

4. Emulsifier

The organic solution of most pesticide crude oil or pesticide ingredients is insoluble with water. Emulsifier is one of the indispensable ingredients in preparation of emulsion, microemulsion, emulsion and other dosage forms. Surfactants used as emulsifiers are mainly non-ionic and anionic mixtures, such as fatty alcohol polyoxyethylene ether or fatty acid polyoxyethylene ester and alkyl aryl sulfonate mixture, while commercially available emulsifiers are mostly mixed with two types of emulsifiers according to the hydrophilic and lipophilic properties of the emulsifiers, according to a certain proportion, agricultural milk 2201, agricultural milk 0203B, etc. This kind of compound emulsifier not only has good emulsification performance, but also the emulsion prepared by it is relatively stable. It is generally believed that this is due to the fact that the pharmaceutical molecules dissolve in the micelles of anionic surfactants and can cause self-emulsification, and non-ionic surfactants adsorb around the organic solvent particles to make the formed emulsion stable.

In addition to the general surfactant solubilization, wetting, dispersion, emulsification and so on, the surfactants in pesticides have other special functions.

1. Basic performance

The physical and chemical properties of various pesticide agents are very different, and the surfactants used to prepare preparations are also different, and not all surfactants can be used in pesticides. Surfactants as pesticide additives should have the following basic properties: first, suitable for the purpose of pesticide processing and application, help to give full play to the drug effect; Secondly, it is safe for crops under actual use conditions and has little toxicity to humans, livestock and fish. Secondly, the preparation is stable, does not deteriorate during the effective storage period, and is easy to use and safe; Finally, the resources are abundant and the cost is low. Therefore, surfactants for pesticides came into being, and are often named special trade names, such as agricultural milk 700#, agricultural aid 2 and so on.

2, the synergism of pesticides

In general, surfactants are the non-biological active components of pesticides. However, since pesticides are applied on crops, surfactants in pesticides will have an impact on target organisms. The synergistic effect of surfactants on pesticides is a manifestation of the effective effect of surfactants on target organisms. Surfactants improve the distribution and adhesion of pesticides on the surface of organisms (plant leaf surface and insect body surface), increase the absorption of organisms to agents, and even increase the transport of agents in organisms, thus improving the biological activity of pesticides.

3, the effect on biology

Some surfactants, such as cationic surfactants, have bactericidal effects themselves, and people have used this property to develop plant growth inhibitors and herbicides. Tea saponin is an excellent nonionic surfactant and a kind of plant insecticide. According to CN1139102A, sodium dodecyl benzene sulfonate (potassium) has a strong bacteriolytic effect, and it can be combined with organic nitrogen compounds with biological activity to obtain a broad bactericide with chemical bacteriolytic effect.

Surfactants have a great effect, but not all surfactants can be used in pesticides, because the surfactants in some pesticides have a harmful effect on crops, so the surfactant for pesticides needs to be selected according to the nature of the original drug, but also to consider its impact on the crop object.