1.1 Extruded granules
The granulation methods of extruded granules include dry granulation and wet granulation. Dry granulation is to use the crystallization water in the material to directly make the powder into granules; wet granulation is to carry out pretreatment such as adding water and kneading the mixed powder raw materials, and then extruder through the screen or orifice plate etc. Extrusion. At present, the extrusion granulation method widely used in the pesticide industry is generally wet granulation. The factors affecting extrusion granulation are the particle size and particle size distribution of the original powder, extrusion granulation aids, humidity, operating temperature, etc. Among them, the particle size and particle size distribution and granulation aids have the most significant effects on extrusion granulation. The new carrier materials currently used for extruded granules include wheat gluten and polyhydroxyalkanoate.
1.2 Coated granules
Traditional coated granules use sand or slag as the carrier, and are prepared by adhering the pesticide technical substance to the surface of the carrier by spray method of granulation tower, fluidized bed coating method, disc coating method or infiltration centrifugation method. Sustained release tends to be less effective. Coated granules with sustained-release function can be prepared by coating a layer of hydrophobic film on the outer layer of the prepared core granules by using novel materials. The material used for coating needs to have the characteristics of good film-forming, strong hydrophobicity, and easy degradation. After coating, it can enhance the sustained-release function of granules, improve drug stability, and mask irritating odors. At present, the materials commonly used for granule coating include ethyl cellulose, resin and amino silicone oil.
1.3 Adsorbent granules
Adsorptive granules are usually prepared by directly adsorbing the original drug on a carrier with adsorption properties, and then prepared by a granulation process. Currently, the commonly used adsorbent carriers include pumice, diatomite, attapulgite and bentonite. Bentonite has been widely used in the field of slow release of pesticides in recent years because of its abundant resources, cheap and easy availability, good environmental compatibility, and adjustable adsorption and desorption capacity for pesticides with different structures and properties.
1.4 Molten granules
After mixing the original pesticide and the carrier material evenly, heating it at a temperature slightly higher than the melting point of the pesticide to make it in a molten state, then dispersing the molten material into droplets, and condensing it to solidify into granules to prepare molten granules. The temperature of the granules prepared by the melt method is usually high, so the original drug that is easily decomposed by heat is not suitable. Currently, the carrier materials used to prepare molten granules include lignin and polylactic acid.
1.5 Gel-type granules
Under the action of physical cross-linking or chemical cross-linking, macromolecules containing hydrophilic groups can form gel particles with a three-dimensional network structure through covalent bonds, hydrogen bonds, van der Waals forces, etc., and encapsulate the pesticide molecules into the three-dimensional network structure. It can improve the stability of the active ingredients of pesticides, reduce the loss and environmental pollution caused by the volatilization and drift of pesticides, and reduce the toxicity to crops and fish. The advantage of gel-type granules is that it can control the release of pesticides by adjusting the mass ratio of carrier material to pesticide, degree of crosslinking, particle size, etc., and the preparation process is simple, which is an excellent and promising slow-release system. Carboxymethyl cellulose, alginate, carboxymethyl chitosan, etc. contain a large number of carboxyl groups, which can be cross-linked with metal ions to form gel particles. The metal ions contained in the cross-linking agent are often nutrient elements required for crop growth. Pesticide molecules are uniformly dispersed in a gel matrix with a three-dimensional network structure, and deliver pesticides in a controllable and stable manner under specific conditions or within a long period of time, providing protection for crop pest control.
