Surfactants are an important component of modern pesticide formulation technology. Without surfactants, it is impossible to have the safety and effective function of today's complex pesticides, and it is impossible to produce benefits, and more talk about environmentally friendly preparations. Such surfactants are commonly referred to as agricultural surfactants or agricultural (medicine) auxiliaries, pesticide emulsifiers.

Surfactants provide many functions such as emulsification, wetting, dispersion, defoaming, and solubilization. The skilled selection of the most suitable surfactants in the processing of pesticide formulations is the key to the successful commercial and technical development of products.

At present, in the traditional pesticide formulations, China is still dominated by emulsifiable concentrates and powdered preparations. The emulsifiable concentrate contains a large amount of volatile aromatic hydrocarbon organic solvents such as toluene and xylene, for example, l. 8% avermectin EC contains nearly 90% xylene solvent. These volatile organic solvents are not only released into the atmosphere during the production and packaging process, but also in the spraying process, and some are left in the soil, causing serious harm and pollution to the environment in which humans live. Similarly, dust generated in the processing and use of powders and wettable powders also poses a problem that is hazardous to human health and environmental pollution. Therefore, in today's advocacy of building a harmonious society and developing an environment-friendly economy, it is particularly important to develop water-based pesticide formulations with high safety, environmental protection and low prices.

1 water-based preparation

Water-based preparations are a class of pesticide processing agents that use water as a medium. These dosage forms have the characteristics of low phytotoxicity, low toxicity, easy dilution, non-flammability, non-explosive, easy to use, easy to measure and beneficial to environmental protection, mainly including water, suspension, water emulsion, microemulsion, suspoemulsion, Suspended seed treatment and suspension microcapsules [2].

The water-based dosage forms of the most popular alternative emulsifiable concentrates and powder preparations at home and abroad are suspensions, water emulsions and microemulsions, while microemulsions are not advocated for development abroad [3].

Suspending agents have more advantages than wettable powders, such as no dust, high suspension rate, safety to operators and users, and environmental safety, relatively low cost, and higher drug efficiency. Therefore, foreign users prefer SC (suspension) instead of WP (wettable powder). Suspending agents are a new type of formulation that is developing rapidly and have great prospects in the world, and the prospect of domestic development of suspending agents is also the same [4].

Water emulsions have the following advantages over emulsifiable concentrates: the efficacy is roughly equivalent or slightly higher. Remove all or most of the (volatile) organic solvents to avoid flammable and explosive problems. Solvent-free odor, low toxicity, no irritation to the eyes, and very low toxicity to human skin. It is safe to manufacture and use, and water is used as a medium instead of organic solvent to reduce environmental pollution. The production cost is greatly reduced, the packaging, storage and transportation costs are low, the economic benefits are very obvious, and the development prospects at home and abroad are also large [5].

2 physical stability of water-based preparations

Although solid preparations (wettable powders and water-dispersible granules) also have stability problems, they are easier to solve than water-based dosage forms. They are always present in solid form, but are temporarily diluted with water to a suspension before use and there is no physical stability problem.

Suspending agents, aqueous emulsions, suspoemulsions, suspension coatings and suspension microcapsules are different, and they always appear in the form of concentrated suspensions, emulsions and suspoemulsions in water. Their physical stability issues have been a key issue constraining the development and production of this dosage form [6].

There are at least three aspects to this physical instability:

(1) stratification and sedimentation of particles (or droplets) due to gravity; (2) agglomeration and coalescence caused by interaction between particles (or droplets); (3) Ostwald ripening ), that is, particles (or droplets) vary in size, solubility is different, and crystal growth occurs in the dosage form.

These problems can be solved by selecting high quality and excellent dispersant (or emulsifier) ​​surfactants to achieve satisfactory results in water based formulation stability.

3 agricultural surfactants (emulsifiers or dispersants)

3.1 emulsifier

More than 10 types of anionic emulsifiers based on calcium alkylbenzene sulfonate can be produced in China and 600# series, 400# series, 600# oil head EO (ethylene oxide), PO (propylene oxide) There are hundreds of non-ionic emulsifier monomers based on block series, BY series and NP series. And they are composed of many compound emulsifiers, which constitute a series of emulsifier products in China, which generally meet the requirements of using emulsifiers in processing emulsifiable concentrates and microemulsions, and can completely replace imported emulsifiers. The anionic surfactants used, mainly calcium dodecylbenzenesulfonate (abbreviated as calcium salt), are widely used throughout the world. Water and anhydrous calcium salts can be produced in China. There is a calcium salt of water, and it is possible to use butanol or isobutanol as a solvent, and to abandon the disadvantage of using methanol as a solvent. Anhydrous calcium salt can make the water content less than 0.5% or even 0.1%, avoiding the disadvantages of processing the emulsifiable concentrate, thereby improving the quality of the emulsifiable concentrate. In the processing of calcium salts, more linear calcium salts have been used in the past, which have better biodegradability, but have the disadvantages that the formulated emulsifiable concentrate is less opaque and narrow in use. Now it has been able to process branched calcium salts, which is superior to linear calcium salts. It has better compatibility with non-ionics, and has the advantages of brighter appearance and wide range of use. The only disadvantage is that it is not easy to degrade [7]. .

It is compatible with other anionic and nonionic screens to prepare almost all microemulsion products. The formulation has a clear appearance and excellent cold and heat storage and stability over time. In the weak oily and insecticidal compound system, the amount of branched calcium salt should be small or not, and other modified anions are better.

Due to the particularity of the microemulsion system, the non-ionic cloud point is too high or too low to achieve the desired effect. The medium cloud point non-ionic compounding effect is better, and the E0 and P0 block series performance is remarkable.

3.2 Dispersant

A dispersant is a surfactant that helps the particles to split and disperse and prevents flocculation and stabilizes the particles. Whether it is a water-based preparation such as a suspending agent, a suspension seed treatment agent and a suspoemulsion, or a solid dosage form such as a wettable powder or a water-dispersible granule (dispersible tablet), a dispersing agent is required.

The dispersing agent is added to the pesticide dosage form (such as a suspending agent) to assist in the dispersion and suspension of the particles during manufacture. When used, it is ensured that the dosage form product is added to the water to be diluted and redispersed into a suitable spray suspension. The dispersant has the ability to strongly adsorb on the surface of the particles, and provides electrical repulsion and block barrier to prevent particle re-aggregation and sedimentation [8].

Dispersants are very different from wetting agents. Wetting agents should be small in molecular weight and can diffuse rapidly during wetting; dispersants tend to have larger molecular weights and can provide many surface points for adsorbing particles.

Since most pesticide solids have a residual negative charge in water, the surfactants commonly used as dispersants are anionic or nonionic, or a mixture of these two types. The most commonly used dispersing agent for wettable powders is sodium lignosulfonate, alkylphenol formaldehyde resin polyoxyethylene ether sulfonate (SOPA), suspending agent commonly used sodium naphthalenesulfonate formaldehyde condensate, alkaryl phenol polyoxyl Vinyl ether phosphates and salts are also used (but less reported domestically).

The successfully developed ZHDISP series dispersant is a polycarboxylate product with a comb structure, which is non-toxic and corrosive.

In the suspension system, it relies on its own anchoring group to firmly adsorb on the surface of the dispersed original drug particles, and forms an electric double layer on the surface of the original drug particles by means of self-ionization to generate electrostatic repulsion, and the long side chain extends into the water to form a solvation layer. The steric hindrance is generated, and the double effect causes the dispersed original drug particles to be stably dispersed in the suspension medium. See Table 1 for application examples.

Table 1 Application examples of ZHDISP series dispersant in suspension

Wood refers to the right effect content. %.

4 domestic new additives application

4.1 WPJ additive

Phosphate ester auxiliaries are a wide range of surfactant auxiliaries commonly used in emulsifiable concentrates and microemulsions of pesticide formulations, but are not suitable for use in processing environmentally friendly pesticide suspensions. However, many surfactant companies in foreign countries have developed a class of phosphate ester auxiliaries, which are used as dispersants in suspension agents as early as possible [9].

Our company has developed this kind of surfactant (WPJ) additive in the “10·5” new additive project, which is used as a dispersing agent for processing suspension products. It has been applied by many domestic enterprises and different pesticide varieties. Better performance than using traditional dispersants. The prepared suspension product has the following advantages: high quality (no delamination and precipitation or bottoming), good fluidity and dilution, high suspension rate (generally above 90%), good storage stability, currently Deeply favored by users of processing suspensions.

The successful development and application of such additives not only enhance the quality of China's pesticide suspension products, but also fill the gaps in China; and it can replace the similar imported additives, but the price is much lower than similar imported additives. The types of suspending agents that have been developed and registered with such additives in China are: 500g/L thiophanate-methyl, 480g/L imidacloprid, 40% carbendazim, 40% chlorothalonil, 40% carbendazim, sulfur, 38% pyrimethanil, 30% chlorfenapyr, 30% beta-cypermethrin, 27.12% basic copper sulfate, 25% chlorfenapyr and 18% buprofezin/imidacloprid.

Last year, it produced and sold more than 200 tons of this additive, and prepared thousands of tons of various SC preparations, which was well received.

4.2 block series

Such surfactant products are often referred to as A-B-A block copolymers, typically in the form of E0-P0-E0 block copolymers, but are not limited to this form. Low molecular weight can be used as emulsifier, high molecular weight can be used as dispersant. However, the number and order of choices A and B must be considered to adjust their HLB values ​​to match pesticides [10]. Our company has undertaken the research and development of the national “11·5” pesticide formulation water-based transformation auxiliary additives, and has achieved a series of development results.

In the E0-P0 block copolymer, the polyoxypropylene chain is a hydrophobic portion, and the polyoxyethylene chain provides a hydrophilic portion. The size of the hydrophobic portion and the hydrophilic portion can be controlled by adjusting the ratio of polyoxypropylene to polyoxyethylene. It is also possible to obtain block copolymers having different properties by changing different forms of the initiator or the blocking group. The most famous of the E0-P0 block copolymers is the Pluronic series. It uses ethylene glycol as a starting agent, and sequentially adds polyoxypropylene and polyoxyethylene to obtain a polyether copolymer product.

The advantages of polyether are odorless, odorless, non-toxic and non-irritating, and have no effect with acid, alkali and metal ions, and have good stability. The disadvantage is poor biodegradability, especially for products with high polyoxypropylene content, which is less biodegradable [11].

We have developed such polyether series additives. Satisfactory results were obtained with EW (water emulsion) and SC new dosage forms using this type of surfactant product, see Table 2.

4.3 Gemini surfactant

Gemini surfactants are a new generation of surfactants, and their unique advantages bring new changes to surfactant applications [12]. The modified bisphenol A polyoxyethylene ether phosphate salt we developed is a new class of gemini anionic surfactants. Used as a pesticide emulsifier and dispersant, it has the characteristics of large molecular weight and wide applicability. The surfactant of this type of double-substructure has the advantage that the adsorption group is adsorbed on the surface of the pesticide particles (or droplets), has multiple adsorption points, has strong adsorption capacity, and is coated on the surface of the agent, and has a strong interface protective film. Its molecular weight is large, and the hydrophilic chain extends into the water phase, which produces a strong steric hindrance effect, prevents the flocculation of the drug particles, and enhances the stability of the system.

4.4 Silicone builder

The successfully developed silicone additive SPEA-205 has a stronger surface activity than ordinary nonionic surfactants and can effectively reduce the surface tension of the solution. The contact angle of the spray solution with the foliage can be reduced, thereby increasing the coverage of the spray. It also increases the adhesion of pesticide droplets on plant leaves, potentially reducing the amount of spray; at the same time, as more liquid adheres to the target, the amount of water required to cover a particular leaf surface is reduced.

SPEA-205D is non-ionic under normal conditions and can be used in most pesticide formulations. The quality indicators are shown in Table 8.

Table 8 Silicone Auxiliary SPEA-205 Quality Index

Usage: (1) SPEA-205 additive can be used as a component in pesticide formulations, the recommended dosage is 1~5%. (2) It can also be used as a tank mixing aid. If the pH of the spray mixture is between 5 and 8, and it is used within 24 hours after preparation, SPEA-205 can exert the best effect, and the recommended dosage is 0.05-0.1%.

It is stable to acids and bases (pH = 3.5 to 9). It can be used in herbicides or insecticides in emulsifiable concentrates, water emulsions and microemulsions. It is a new type of high-efficiency pesticide additive. It can be compared with imported silicone additives. The application prospect is very broad and worthy of attention.

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