From May 23 to 24, 2019, the fourth "Jinwang Cup" pesticide preparation processing technology and equipment application exchange conference hosted by Shandong Provincial Pesticide Industry Association was held in Dezhou, Shandong. The conference was named by Jiangsu Jinwang Intelligent Technology Co., Ltd. and specially co organized by Shandong Lvba Chemical Co., Ltd. This conference aims to train pesticide manufacturers to understand production, technology, equipment, process Complex talents who understand management.
The R&D and production of pesticide preparations are closely linked to the national policy guidance. Under the background of zero growth of pesticide use and increasing environmental pressure, it is necessary to adopt new safety and environmental protection additives or develop new dosage forms. The research and development of pesticide preparations has a certain relationship with the current trend of pesticide use reform. Under the current trend of accelerated land circulation, labor shortage and increased employment costs, improving the efficiency of pesticide use is one of the effective solutions.
The quality of pesticide formulations and preparations is the key factor to determine the effect and value of pesticide products. Therefore, the development of pesticide products needs to understand the structure, physical and chemical properties, mode of action, toxicity, etc. of the original drug. At the same time, the quality of the original drug and the main content of the preparation directly affect the performance of the preparation. Generally speaking, for a specific original drug, the higher the content of the preparation, the more difficult it is to control the performance; The quality of the original drug is too low, its proportion in the preparation is relatively high, and the impurity situation is complex, so it is difficult to grind high-quality and high content preparations. When talking about the screening principle of auxiliary agent system, researcher Zhang Guosheng of Shenyang Research Institute of Chemical Industry pointed out that, except for a few pesticides with high volatility and high solubility in water that can be used directly, the vast majority of pesticide technical drugs must be processed into corresponding dosage forms before they can be used. After the formulation is determined, according to the structure (charge distribution of active groups and inactive groups), physical and chemical properties, mode of action and action targets (chemical composition, distribution density, leaf age, nutritional status, environmental conditions, etc. of the active components, a large number of formulation studies and performance test experiments were conducted on the effects of different wetting and dispersion systems on the preparation performance and target, and combined with the results of biological activity measurement, Determine the auxiliary system and dosage suitable for different dosage forms, and finally obtain the formula composition of the preparation. In addition, after the determination of the main auxiliary agent, the role of the auxiliary auxiliary agent cannot be ignored. At the same time, the indoor biological activity comparison test is carried out. After the formula composition is determined, the sample is amplified, and long-term observation (particle size change, appearance, viscosity, wall hanging, agglomeration, etc.) is also required. Production process research is also required.
The preparation samples prepared with the selected appropriate wetting and dispersing agent varieties not only have a high degree of dispersion of the active ingredients of pesticides, but also have a large amount of penetration into organisms, which is specifically reflected in: on the one hand, the active ingredients can be rapidly, evenly and stably dispersed in the carrier, maintaining a good suspension, dispersion, appearance stability and thermal storage stability; On the other hand, it can make the spreading and adhesive force of its liquid medicine on the surface of the plant body relatively strong, resist rain wash, increase the retention amount of pesticides on the surface of the plant, extend the retention time and improve the penetration ability of the plant epidermis, promote the absorption of the agents by organisms, so that it can play its biological activity to a large extent, reduce the use dosage and reduce the environmental pollution. Although the wetting and dispersing agent itself has no biological activity, it is an indispensable additive in the formulation. It can not only improve the physical and chemical properties of the preparation, improve the efficacy, but also expand the application range of pesticide raw drugs and reduce environmental pollution.
Finally, Researcher Zhang believes that the preparation system has narrow particle size distribution, good long-term storage stability, and the diluted solution has good wetting, spreading, dispersion, retention and permeability on the target, which can better assist the active component to play its biological activity, greatly reduce the dosage and improve its compatibility with the environment.
Zhang Guosheng, Researcher of Shenyang Research Institute of Chemical Industry
With the improvement of people's requirements for the environmental safety of pesticides, water-based pesticides have become an important development direction. In this context, microemulsions that partially or completely replace organic solvents with water emerge as the times require. Professor Chen Fuliang from the Institute of Plant Protection, Chinese Academy of Agricultural Sciences shared the "common problems and solutions of water emulsion and microemulsion formulation".
Water emulsion is a kind of dispersion system with unstable dynamics and thermodynamics. Stratification, sedimentation, flocculation, austempering, coalescence and demulsification are common problems in water emulsion formulation. Stratification and sedimentation are phenomena that disperse phase particles often float or sink during storage, also known as emulsion, which belong to dynamic instability. The reason is the density difference between two phases (caused by gravity). The solution is to resist gravity: increase the viscosity of the medium, the thickener can increase the viscosity of the water emulsion system, reduce the diffusion coefficient, reduce the collision frequency of the droplets, and reduce the speed of stratification and sedimentation. However, this thickener should be selected carefully through tests to not only keep the water emulsion free of stratification or sedimentation, but also not make the system viscosity too large, which will affect its dumping and emulsification dispersivity; Increase the amount of emulsifier, reduce the particle size of the droplet, enhance Brownian motion, and reduce the stratification and sedimentation of the preparation; Adding density regulator to match the density of oil phase and water phase is an effective way to reduce stratification and sedimentation. However, when the density difference of oil phase is large, it is of little significance to change the sedimentation rate by reducing the density difference between dispersed phase and dispersion medium. When the density difference is small, adding density regulator can significantly reduce the sedimentation rate.
Flocculation refers to the phenomenon that liquid droplets gather to form loose aggregates, which can be restored to a uniform emulsion after vibration and shaking. This is because the dispersion interaction force between liquid droplets refers to the attraction generated when non * molecules are close to each other. Another situation where flocculation occurs is that dispersed oil droplet particles are adsorbed and bridged on linear macromolecules, which leads to particle sinking. The flocculation solution is anti aggregation: add anionic surfactant, form a double electric layer around the droplets, cover the surface of the oil phase droplets with charged groups, and generate electrostatic repulsion to prevent the droplets from aggregation; Add polymer emulsifier to form a thick and firm adsorption layer in the system, producing steric hindrance effect. The condition for strong adsorption is that the polymer is not dissolved in the continuous phase; The thickener is added to reduce the diffusion speed of oil droplet particles, reduce the collision frequency of droplets, and improve the flocculation of dispersed droplets.
Coalescence refers to the destruction of the boundary film around the droplets, and the droplets coalesce into large droplets, which belongs to thermodynamic instability; Demulsification is the further development of coalescence of droplets, which makes emulsion become oil-water two-phase separation. Coagulation and demulsification are irreversible processes due to the destruction of the interfacial facial mask. The coalescence solution is to strengthen the interfacial facial mask: add co emulsifier, and the lateral action of surfactant and co emulsifier adsorbed on the interface will enhance the strength and elasticity of the interfacial facial mask; Anion, polymer emulsifier and mixed surfactant are used. Anion expands the thickness of the electric double layer, and polymer increases the steric hindrance. Mixed emulsifier can strengthen the transverse effect of the interface facial mask and enhance the mechanical strength of the interface facial mask, improve the interface viscosity, increase the interface elasticity, and make the interface facial mask have a high expansion elasticity; The addition of hydrophilic powder can not only improve the film strength, but also enhance the film properties.
Water emulsion is a thermodynamic unstable dispersion system, which can maintain dynamic stability for a long time. However, as time goes on, the size and distribution of droplets will move towards larger droplets. This process of consuming small droplets to form larger droplets is called Austenitic ripening. The austempering solution is uniform particle size distribution: increase the amount of surfactant, reduce the interfacial tension to make the oil droplet size distribution more uniform, reduce the driving force of austempering, and slow down the austempering; The addition of solvent with lower solubility will help to reduce the solubility of oil phase and slow down the diffusion rate of oil molecule dissolution, which is the driving force of austenite ripening; Use polymer surfactants to increase the thickness of the adsorption layer, reduce the surface area of "exposed" droplets, increase the steric hindrance, and improve the spatial stability, such as block or comb graft polymers.
How to adjust the unqualified products? Flocculation, stratification and sedimentation can be properly adjusted and reprocessed through the above coping strategies; For unstable phenomena such as coalescence, demulsification and austempering, which are irreversible processes, the product can only be scrapped. Demulsification occurs during production after passing the small test. The solution is to increase the dosage of emulsifier; Replace the production equipment, use the homogenizing emulsification machine, or connect the pipeline shear with the vertical shear. Water separation occurs after production. The solution is to adopt pipeline shear and external shear connecting devices, or adopt homogeneous emulsification to control the particle size of lotion dispersion system to a narrow range; If it is caused by insufficient shear time, the shear time can be appropriately extended and the shear rate can be increased. If the small test is qualified and oil slick occurs during production, the combination of pipeline type high speed shear and intermittent type high speed shear shall be used to solve the problem.
Professor Chen also introduced the characteristics of the second generation of water emulsion: no shearing, the fluidity is comparable to microemulsion; The particle size is smaller than that of water emulsion, which is closer to microemulsion, also known as submicron emulsion; The dosage of emulsifier is higher than that of water emulsion, and its stability is lower than that of microemulsion and higher than that of conventional water emulsion. It is pointed out that most pyrethroid pesticides can be processed into second-generation water emulsion.
Professor Chen summarized the research and development experience of water emulsion as follows: ① According to the basic principle of emulsion formation, mechanical energy and interfacial tension are the key factors affecting the formation of lotion, while the large size or uneven distribution of oil droplets is one of the main reasons for the instability of water emulsion; ② For solid technical drugs, the first step is to select appropriate solvents. Generally, organic solvents with high solubility are selected to achieve complete dissolution and save solvents; ③ If the surfactant is selected properly, there is a wide selection range of co emulsifiers and water quality; ④ If the problem of physical stability cannot be effectively solved, it can be considered to add tackifier in the preparation.
For the low temperature stability of microemulsions and the stability of lotion, Professor Chen shared the measures to improve the low temperature stability of microemulsions: increase the amount of solvent. For the effective components that are difficult to dissolve in general organic solvents, there is a stable dissolution rising point of organic solvents; Adjust the hydrophilic and lipophilic balance of surfactants. High temperature needs hydrophilic, while low temperature needs lipophilic; Select appropriate cosurfactant, and some effective ingredients with special physical and chemical properties have certain selectivity for cosurfactant. So how to improve the stability of microemulsion lotion? ① Using mixed solvents, an effective way to solve the stability of lotion; ② Increase the amount of surfactant to improve the stability of the interfacial facial mask; ③ Reduce the content of effective ingredients, which is equivalent to more emulsifiers wrapping oil droplets, improving the mechanical strength of the facial mask; The stability of lotion is closely related to the particle size distribution of microemulsion oil beads, but not to the particle size.
Professor Chen summarized the research and development experience of microemulsion as follows: ① It is required to prepare a wide transparent temperature range, mainly depending on the selection of surfactants and cosurfactants; ② High temperature stability requires highly hydrophilic surfactant, while low temperature stability requires highly lipophilic surfactant; ③ In order to prepare qualified microemulsions, it is necessary to adjust the hydrophilic lipophilic balance (HLB) of the system; ④ The upper limit of transparent temperature is the determination of cloud point, and the lower limit of transparent temperature is the determination of low temperature stability. The stability of lotion is only for a few active ingredients with special physical and chemical properties.