Microcapsule suspension (CS)
Microcapsule suspension (CS)
Microcapsule suspension is a kind of microcapsule with semi permeable membrane formed by wrapping pesticide active substance (core) with polymer material as the wall or membrane through chemical, physical or physicochemical methods, and they are stably dispersed and suspended in water as a continuous phase in a certain concentration, which is called microcapsule suspension.
Pilarquim is the "most professional supplier of agricultural microencapsulation product R&D and production in China". In the field of agricultural microencapsulation, Pilarquim not only has the most mature and advanced technology, but also has many registered products, and its industrialization level is also in the leading position in the industry. As a leading enterprise in the research, development and production of agricultural microcapsules in China, the microcapsule products that have been put on the market at present include Minggong, mingdaoshou, jinggongfu, delika, Deliang, Lishuang, Lizao, miaowanjin, Miaozhen Compared with domestic and foreign companies, the microencapsulation products of Pilarquim are leading in the industry.
Technical background of pesticide microcapsules
The traditional dosage forms have a common disadvantage, that is, the effective ingredients are directly exposed to wind, rain and sunlight after application, easy to decompose, volatilize, and the duration of insecticidal effect is short. The duration of validity is only 1-3 days for the short and 5-15 days for the long. Because of these shortcomings, in order to improve the insecticidal effect, the traditional method is to increase the concentration of effective ingredients. The increase of concentration not only increases the production cost, but also increases the toxicity of pesticides to a very dangerous level, which brings great harm to people's production and life.
In order to overcome the shortcomings of high toxicity and high residue of chemical pesticides, many companies turn to bio pesticide research. However, due to the limitations of the dosage forms, the high volatilization and photolysis of Biogenic Pesticides have become a major obstacle to widespread application. Pesticide microencapsulation technology arises at the historic moment.
2.Brief introduction of new technology of pesticide microcapsule
Generally speaking, microencapsulation is to wrap the effective ingredients of pesticides with high molecular materials (called encapsulation materials or wall materials), just like dumplings, the effective ingredients of pesticides become the stuffing of dumplings, and the wall materials become the skin of dumplings. The semi permeability of wall material can prolong the duration of pesticide, delay the degradation rate of effective ingredients, improve the insecticidal effect and reduce the toxic and side effects. The specific benefits are as follows:
Because the pesticide effective body is wrapped in a film, it is not easy to photodegradation, hydrolysis, oxidation and volatilization, and the duration of validity is prolonged, which has more obvious effect on biological pesticide.
2.2 Sustained release
After the microencapsulation of pesticide, because the wall material is semi permeable, the pore size or wall material thickness can be controlled artificially according to the physical and chemical properties of the effective components, so as to effectively control the sustained-release dose and time.
2.3 Reduce toxicity
After microencapsulation of pesticides, the general toxicity can be reduced by 10-20 times, and some can be reduced by several hundred times. In particular, the safety of some highly toxic pesticides can be greatly improved by microencapsulation.
2.4 Cost reduction
After the microencapsulation of pesticide, the use of the original drug can be reduced to 1/2~1/3 of the original amount, and the medium can be changed from organic solvent to water, which can effectively reduce the product cost.
2.5Insecticidal effect increased
The effective component concentration of microcapsule pesticide capsule is generally 5-15% or even higher, and its effective ingredients are more concentrated than those of emulsifiable concentrate. Once a high concentration capsule touches the insect, it will be more susceptible to insect poisoning than other forms, and the knockdown speed will be improved.
After microencapsulation, the general insecticidal effect can be increased by 15-30%, the use amount of the original medicine can be reduced by 50% at least, the duration of efficacy can be extended by 2-8 times, and the maximum can reach 250 days. The technology can also be used to extend the holding period of herbicides, fungicides, etc.
2.6 Reduce the times of applying medicine and reduce the cost of agriculture
Because the effective period of microcapsule pesticide is prolonged, the insecticidal effect is improved, and the number of times of pesticide use in a growth cycle is greatly reduced, so the cost of pest control is reduced, labor and effort are saved. For example, the whole growth period of cotton only needs to spray 2-3 times of microcapsule pesticide. Some of the other dosage forms spray once a week, or even once every three days.
Reasonable control of pesticide duration to meet the needs of different control objects
2.8 Reduce the harm of pesticides to the environment
Because of the absence of benzene, toluene and other highly polluting organic solvents, combined with the reduction of toxicity, the number of treatments is reduced, greatly reducing the harm to the environment
2.9 Make biopesticides more suitable for market demand
Due to the improvement of Chinese living standard, organic food is more and more popular. Chemical pesticides and fertilizers shall not be used in the production of organic food, but only biological pesticides and organic fertilizers. Due to the high cost, low yield, expensive price, poor effect and short duration of the biopesticides, there are many difficulties in practical application. If the effective components of biopesticides are microencapsulated, it is not easy to volatilize and lose, it is not easy to oxidize and photolysis, it can prolong the period of validity, improve the insecticidal effect and reduce the production cost, which is conducive to the popularization of biopesticides.
2.10 Make it possible to mix raw drugs with different pH values
The combination of different active ingredients can greatly improve the efficacy of insecticides, but due to the different pH value, the combination is often difficult. Most of the synthesized pesticides are stable in acid condition and easy to degrade in alkaline condition. Alkaloids are mostly used as effective substances in plant pesticides. Some of the insecticidal active ingredients are very alkaline, pH value is 11.3, some are neutral or weak acid. The microencapsulation technology can first encapsulate the effective components of pesticides with different pH values, and then compound them to solve the problem of neutralization, which greatly increases the prospect of new compound pesticide varieties research and development.
2.11 Make pesticides more suitable for water quality
The effect of the same pesticide in southern China is quite different from that in the north. The main reason is different water quality. The south water quality is acid, pH 5.8-6.5, while the north is dry and rainy, the water quality is alkaline, and pH is 7.3-8.3. In many places, the pH value is around 7.8.
Most of the pesticides are weakly acidic. Under the condition of weak acid water in the south, the amount of pesticide used is small and the effect is good. However, the same pesticide has greatly decreased the efficacy of the drugs in the alkaline water area of the north, and the usage has increased by 1-3 times, and the effect is not as good as that of the south. After microencapsulation, the influence of different water quality on the stability of pesticides was greatly reduced or even not affected.
3. Preparation of agricultural microcapsules
The new method and technology of microcapsule preparation have been one of the efforts of many researchers. At present, there are three kinds of preparation methods: physical chemistry, chemical methods and physical methods.
3.1 Physical and chemical methods
This method is used to form vesicles in liquid phase. That is, adding another substance in the mixture of the core and the material (such as sodium alginate), or using other appropriate methods to reduce the solubility of the material and form a new phase around the core material. According to the different methods of forming new phase, it can be divided into single coacervation, complex coacervation, solvent non solvent method and so on.
3.1.1. Simple coacervation
The single coacervation process consists of three consecutive steps: A. dispersion of the coated material into the polymer solution; B. precipitation of the coacervation layer to the core material; C. coacervation of the coacervation layer. A polymer is used as the material to disperse the core material into the material of the capsule, and add strong hydrophilic electrolyte such as ethanol, propyl alcohol, strong hydrophilic non electrolyte or sodium sulfate and ammonium sulfate. Because of the combination of water and coagulant in the film, the solubility of the capsule decreases and the microcapsules are formed. A suitable curing agent is added to solidify the coacervation capsule so as to keep the capsule shape for a long time.
The main factors that affect polymer materials are concentration, temperature and electrolyte. Increasing the concentration and temperature of the capsule is beneficial to the gel. The relationship between the temperature and the concentration of the capsule is: the higher the concentration is, the higher the temperature limit of the gel is. For example, 5% gelatin solution is in 180C gel, while 15% gelatin solution is in 230C gel. In electrolytes, anion plays a strong role in promoting gelation. In common anions, sulfate ion promotes gel formation, and chloride ion takes the second place.
3.1.2. Complex coacervation
In this method, two kinds of oppositely charged polymer materials are used as the materials to disperse the core (suspension or emulsification) in the aqueous solution of the capsule. Under certain conditions, oppositely charged polymers cross-linked to form the composite (i.e., the composite material). The solubility is reduced, and the pouch is condensed from the solution.
When the microcapsules are prepared by single coacervation and complex coacervation, the surface of the core should be wetted by the solution of the capsule. Therefore, wetting agents can be added in some cases. In addition, the temperature should be controlled to keep the condensate fluidity. This is also a necessary condition to ensure good pouch formation. Natural polymers, such as alginate, pectin and so on, contain cellulose or CAP or CMC-Na, which can contain COO- or COOH. They can be complex coagulant with gelatin, so they can also be used as microcapsules.
The advantages of agglomerating method are that the pesticide active substance can be either liquid or solid (it must be stable in water), the encapsulation material is cheap and easy to obtain, the cost is low, the polymer shell can degrade rapidly in nature after application, which should be the direction of the development of microcapsule technology, and the disadvantage is that the process condition control is complex.
3.2 Chemical method
The chemical method is to form the emulsion microbeads by taking the core material as the dispersed phase, and to form polymerization and condensation reaction on the interface with the continuous phase (usually water), so as to form the wall of the capsule. Therefore, it is also called interfacial polymerization, which can be divided into: interfacial polymerization, location polymerization and radiation chemistry.
3.2.1. Interfacial polymerization
Interfacial polymerization is the most commonly used method for the preparation of pesticide microcapsules. The process is as follows: the active substances and the appropriate polymer wall materials (monomers) are dissolved in the organic solvent which is not mutually soluble with water (some crude oil with bottom viscosity does not need solvent), and then the oil phase is added into the aqueous solution containing the appropriate emulsifier and protective glue under the shear condition to form a water bag In the form of oil or water in oil, a certain particle size shall be controlled as required. Another water soluble wall material was added into the aqueous phase. The two materials react at the oil-water interface and form the polymer capsule wall around the droplets containing active substances. This method can be carried out quickly at room temperature, and the capsule wall is regular, uniform and hard.
3.2.2. In-situ polymerization
Also known as in-situ polymerization, in the positioning polymerization, polymer monomers and prepolymers are placed in the oil phase, and the interfacial polymerization is initiated by raising the temperature or using a surface-active acidic catalyst. If the active ingredient is solid, the solid active component is dissolved in an organic solvent which is insoluble with water before the monomer or prepolymer is added. The asymmetric wall is produced by the positioning polymerization process, and a thin, dense outer layer is lifted from a thicker sponge lower layer. For microcapsules with a diameter of 10μm, the outer membrane thickness may be close to 0.05μm and the inner wall thickness is close to 0.5μm. When the inner layer provides mechanical support, the outer layer determines the diffusion rate. It is necessary to heat up the capsule wall for a certain period of time (usually under 500C 3H).
Also known as in-situ polymerization, in the positioning polymerization, polymer monomers and prepolymers are placed in the oil phase, and the interfacial polymerization is initiated by raising the temperature or using a surface-active acidic catalyst. If the active ingredient is solid, the solid active component is dissolved in an organic solvent which is insoluble with water before the monomer or prepolymer is added. The asymmetric wall is produced by the positioning polymerization process, and a thin, dense outer layer is lifted from a thicker sponge lower layer. For the microcapsules with a particle size of 10 μm, the thickness of the outer layer may be close to 0.05 μm, and the thickness of the inner layer wall may be close to 0.5 μm. When the inner layer provides mechanical support, the outer layer determines the diffusion rate. It needs to be heated for a certain time (generally at 500C for 3h) to form the capsule wall.
3.3. Physical method
Spray drying is a method of drying a solution, emulsion, suspension or slurry into a powder drying product by a single process. The microencapsulated materials used in spray drying include liquid paraffin, cellulose acetate, lemon oil and hydroxylated dextrins.
The principle of spray drying method is that the wall material forms a network structure when it is heated and plays a sieving role. Small molecules, such as water and other solvents, are evaporated by heat and move through the mesh, while the larger core material is trapped in the net. By selecting the mixture of different substances or several substances as wall materials, the size of the mesh hole can be controlled artificially and the purpose of wrapping different molecular sizes can be achieved.