In pesticide applications, what is the most promising sugar-based surfactant?

Pesticide preparation technology and development of agricultural surfactants

Pesticides are a mixture of one or several substances used to prevent and control harmful organisms that endanger agriculture and forestry. Pesticides usually need to be processed into formulations before they are applied. The components of pesticide formulations generally include the original drug or parent drug, surfactants, solvents or fillers, and other functional additives such as thickeners, defoamers, etc. Among them, surfactants play a vital role in dispersing, stabilizing, wetting and spreading, and delivering drugs, and can be described as the "MSG" in the processing of pesticide additives.

In the 1950s, mankind successively developed chemical pesticides such as organochlorine and organophosphorus. For convenience, these pesticides are processed into powders, wettable powders, emulsifiable concentrates and other dosage forms. In order to develop these pesticide formulations, corresponding supporting surfactants have been gradually developed and used, such as Nongru 100#, Nongru 500#, Nongru 600#, natural fatty alcohol sulfonates, etc., and even some primitive bone glues, Saponin powder, etc., was also introduced into the pesticide industry to improve the effect of pesticide application, and finally formed the original pesticide formulation technology.

In the 1970s, people began to gradually develop water-based environmentally friendly formulations, mainly including suspensions, water emulsions, microemulsions, granules, etc. These formulations reduce the use of a large number of solvents and fillers added in traditional pesticide formulations, and require matching surfactants. Therefore, during this period, many types of fatty alcohol polyethers, block polyethers, and phosphate esters have been developed. , Sulfate, naphthalene sulfonate, polycarboxylic acid and other surfactants, and applied to pesticide formulations, successfully solved the dispersion and stability of new formulations such as suspension agents, water emulsions, granules, etc.

At the beginning of the 21st century, the research and development of green and ecological pesticide preparation technology started. The new pesticide formulation technical requirements conform to the concepts of sustainable development such as green, ecology and safety. The research thinking of pesticide formulation technology has shifted from focusing on dispersion and stability in the 20th century to drug delivery in the 21st century; at the same time, it has also changed from the research and development of new formulations in the past to the research and development of new formulations. In the process of research and development of new pesticide formulation technology, the research and development of new surfactants is still the core issue, and it is necessary to develop products with high drug delivery efficiency, green and environmental protection. Some types of surfactants will face the fate of being banned because they are not easily degradable in the environment and have high biological toxicity. Eye irritation and high toxicity to aquatic organisms have been banned from pesticide preparation products in major countries such as Europe and the United States. Different from the previous two types of surfactant products, the raw materials of bio-based surfactants are derived from natural substances, with good biocompatibility and conductivity, and are one of the new types of surfactants most suitable for new pesticide formulations.


Sugar-based surfactants

Biological surfactants generally refer to a class of surfactants whose production raw materials or main raw materials are derived from natural substances such as animals, plants, and microorganisms, such as extracts of plant roots, stems, leaves, and fruits. These extracts themselves or after simple derivatization have both hydrophilic and lipophilic surface activity. Biological surfactants not only have the properties of solubilizing, emulsifying, wetting, foaming and dispersing surfactants, but also have low toxicity, biodegradability and ecological safety compared with other surfactants such as chemical synthesis. , Good environmental compatibility and other advantages. Common biological surfactants include castor oil polyether, even-carbon linear fatty alcohol polyether, animal and vegetable oil fatty acid polyether, cardanol polyether, alkyl glycosides, glycosyl glycolipids, chitosan oligosaccharides and derivatives Things etc.

Among biological surfactants, sugar-based surfactants have a wide range of raw materials and are a class of products with development prospects. Sugars are aldehydes or ketones containing multiple hydroxyl groups, and the organic compounds that become one of the two after hydrolysis can generally be referred to as sugars. Since most sugar compounds can be represented by the general formula [C(H2O)]n, they are often called carbohydrates. Sugars include monosaccharides, disaccharides, oligosaccharides and polysaccharides. They are widely found in plants such as fruits and vegetables, as well as honey and animal milk, and they are widely found in nature. Glycosurfactant refers to a substance that contains a sugar-based structure or is modified or derivatized on the basis of a sugar-based structure to have surface activity. Commonly used sugar-based surfactants in pesticides that have application prospects are sorbitol fatty acid esters, sorbitan fatty acid esters (Span), polyoxyethylene-sorbitol fatty acid esters (Tween), and sucrose fatty acid esters , Alkyl glycosides, alcohol ether glycosides, glucamide, rhamnose, sophorolipids, trehalolipids, cellobiose lipids and mannose erythritol lipids.


Sorbitol fatty acid ester and sorbitan fatty acid ester

Sorbitol, also known as sorbitol or glucitol, is produced by hydrogenation of glucose and is a sugar alcohol that can be metabolized by the human body. Commonly used surfactants produced from sorbitol and fatty acids are sorbitol fatty acid esters and sorbitol fatty acid esters. Sorbitol fatty acid ester is generally directly prepared by esterification reaction of sorbitol and fatty acid chloride. Sorbitol fatty acid ester is insoluble or hardly soluble in water, suitable for fiber softener, but not suitable for emulsifier. Sorbitan fatty acid ester is a very important non-ionic surfactant in various industries, and its trade name is Span.

Sorbitan fatty acid ester, also known as sorbitan fatty acid ester, is generally obtained by esterification of sorbitol and fatty acid under alkaline and heating conditions, and dehydration of sorbitol at the same time of esterification. According to the type of fatty acid and the reaction ratio of fatty acid to sorbitol, the reaction can prepare surfactants with different structures and properties. Common fatty acids include lauric acid, palmitic acid, stearic acid and oleic acid, etc. The different sorbitan fatty acid esters shown in Table 1 are obtained by adjusting the ratio of reaction materials.

The characteristic of sorbitan fatty acid ester is strong oil solubility. Such products are generally insoluble in water, soluble in a variety of organic solvents, have excellent emulsification and dispersibility, and are suitable for use as water-in-oil (W/O) emulsifiers. This type of nonionic surfactant is mainly used as an emulsifier in the pesticide industry, and can be compounded with other water-soluble surfactants, and has a wide range of applications in the pesticide industry.

Domestic and foreign companies that develop and supply sorbitan fatty acid esters include British Croda, German Cognis (now BASF), Rhodia (now Solvay), etc. Domestic companies include Zhongshan Chemical, Jiahua Chemical, Haian Petrochemical, Shandong Zibo and Many manufacturers such as Xingtai, Hebei.


Polyoxyethylene-sorbitan fatty acid ester

Sorbitan fatty acid ester has strong oil solubility and hydrophobicity, and is generally insoluble in water. If ethylene oxide is added to its structure, the hydrophilicity will increase, and the number of ethylene oxide molecules added will increase. , The more hydrophilic and soluble in water. The common polyoxyethylene-sorbitan fatty acid ester uses sorbitan fatty acid ester (Span) as the raw material and is prepared by adding ethylene oxide. The trade name is Tween. There are also companies that use different synthesis processes. For example, CRODA uses sorbitol as the raw material, first adds ethylene oxide, and then esterifies with fatty acids. At the same time, it controls sorbitol not to undergo dehydration during the refined synthesis process to synthesize Cirasol products. . According to different fatty acid types, ethylene oxide addition number, and the molar ratio of fatty acid and sorbitol reaction, different products can be produced. Usually fatty acids include lauric acid, palmitic acid, stearic acid, oleic acid, etc. The addition number of ethylene oxide ranges from 4 to 20.

Common Tween series products are generally soluble or dispersed in water, and are soluble in most organic solvents, such as alcohols and aromatic solvents, but are insoluble in mineral oil and grease. Some special grades are soluble in mineral oil and grease, such as products with low addition number of ethylene oxide and CRODA's Cirrasol series products.

Polyoxyethylene-sorbitan fatty acid ester has good emulsification, dispersion and stability properties, and is often used as an emulsifier, dispersant, and synergist in the pesticide industry. Used in most emulsifiable concentrates as a safe and environmentally friendly emulsifier, instead of alkylphenol polyether and agricultural milk series. Used as a synergist in soluble liquids, such as imidazolinone products (now soluble liquid), polyoxyethylene (20) sorbitan monolaurate is used as the main booster Effect agent. Used in dispersible oil suspensions, as emulsifiers and dispersants, such as CRODA's Cirrasol series G-1086 products, as high-efficiency emulsifiers and dispersants, used in the copper preparations of dispersible oil suspensions.

Domestic and foreign companies that develop and supply polyoxyethylene-sorbitan fatty acid esters include British Croda, German Cognis (now BASF), etc., and domestic companies such as Zhongshan Chemical, Jiahua Chemical, Haian Petrochemical, Shandong Zibo and Hebei Xingtai. Many manufacturers.