Water dispersible granules (WG) is a rapidly disintegrating water was added and dispersed into a suspension of the granular preparations , also called dry suspensions . The first product is the world’s pesticide WG 1980s by the Swiss Ciba – Geigy produced herbicide atrazine and the U.S. company DuPont herbicide metribuzin . WG formulations active ingredient content was very low , and higher manufacturing costs, subject to technical and technological level of restriction requires the use of a particular pesticide active ingredient ( high melting point, low solubility in water, such as atrazine ) can be processed .
After the pesticide WG generated widespread attention abroad , in the late 20th century a safe , environmentally friendly and alternative suspensions and wettable powders and water mass developed new formulations. With the continuous development of new additives and pesticide use , as well as advances in granulation technology and equipment , and now there are hundreds of different business on the physical and chemical properties of the pesticide active ingredient products. WG pesticide market share and the number continues to increase rapidly in the U.S. registered product formulations Nearly 20% of WG products, while the U.S. and other European countries about 10% of registered products is WG formulations, some have been more than 10 %, and is continually increasing. When diluted in water , can quickly disintegrate after stirring , the particle size distribution obtained by dispersing a suspension of 1-10μm . WG has the following characteristics : ( 1 ) no solvents and dust emissions, reducing the pollution of the environment , the safety of the producer ; ( 2 ) active ingredient content, relative density , small size , packaging, storage , easy to transport ; ( 3 ) into the water rapidly disintegrating , with good dispersion ; ( 4 ) there is a certain hardness and strength , not easy to produce dust ; ( 5 ) excellent suspension, just a little stir to form a homogeneous suspension , which suspension rate up to 90% ; ( 6 ) good re- dispersion, long and stir again to form a uniform suspension when the suspension is not used again without affecting efficacy ; good ( 7 ) storage stability , low toxicity of the product and improve the safety.
Since the WG has more advantages , so more and more welcomed by the market . Currently Technically , both the hydrophilic, lipophilic , the raw powder is a solid or liquid oil , can be processed into WG. Although its processing technology is more complex, larger investment costs , higher costs, but its outstanding safety, excellent performance and a favorable resistance to environmental protection is unmatched by other forms , so WG formulations market share continues expand its market prospects are very attractive development prospects .
WG formulations typically consists of the following components: 50% -90 % active ingredient ; wetting agent 1% -5 % ; dispersing agent and a binder 5% -20 % ; 0-15 % disintegrant ; other additives 0 – 2% ; filler to 100 %. If the active ingredient is a liquid pesticides original drug , it is necessary first with an inert carrier ( such as clay , silica gel ) adsorption , and then the way the original drug solids processing . Water-soluble active ingredient is processed into a water-soluble filler soluble granules , water -insoluble active ingredients directly processed into the WG. WG formulations of the active ingredient content is generally 60 % -90 %.
WG granulation process there are two categories : dry and wet . Dry the first pesticide active ingredient mixed with other auxiliary materials , the use ultrafine grinding mill to obtain the desired airflow powder particle size , go granulation. This method has the turntable granulation , high intensity mixing granulation, extrusion granulation method. Is wet with the other pesticide active ingredient in water together with auxiliary materials finely crushed to obtain the desired slurry was then granulated , can also be obtained by a dry process and then to the granulated powder to prepare a slurry . The fluidized-bed granulation method , fluidized spray drying granulation and spray drying granulation method . In addition, there are other granulation methods ( such as freeze-drying , compression, etc. ) are used to process the granules, but are not suitable for processing agricultural products WG . In deciding what the granulation process used , and the active ingredient must first consider the physical properties of the additive , and the processing of these factors determines the particle shape, size and properties of the final product ( such as dust resistance, re-dispersibility , etc.). WG particles dispersed in water should be within a certain period of time to achieve complete dispersion , in general, different water temperature and water quality, fully dispersed within two minutes .
Multiple use of foreign extrusion granulation method and spray drying method , an extrusion method using up Youyi , 27.5 % spray- dried , agglomeration, melting , fluidized bed granulation, disk , respectively 14.5% , 10.5 %, 8.5 %, 5 % and 3% , accounting for 29.5% of the other methods . Was extruded at a period of time considered optimal granulation method , the smaller the size of the plant and requires a low amount of air , and spray drying was removed from the economic , physical and chemical properties of the product ( such as a suspension , dispersion , disintegration , etc. ) are better than the extrusion method. However, higher yields can be obtained by extrusion , and can be intermittent operation . Currently in the UK , the U.S. , Europe or Japan, extrusion granulation has become a mainstream technology, we can learn from . WG in developing countries very quickly.
In just a few among the major forms are being replaced gradually become dry powder, wettable powder , cream and suspending . Especially in the U.S. and the UK , in 1993 and 1998 , the U.S. market share WG formulations were 13 % and 19% , while Britain were 5 % and 11% . Years almost 20% among the U.S. , more than the WP ( 1993 / 1998 , respectively, a wettable powder of 16 % and 15% ) . Foreign companies also increased agricultural market development in our country , in our WG registered varieties from four to the current nearly 40 varieties in 1998 .
WG formulation of the research and development, production and application of greatly lags behind other countries, mainly by the following factors constraining : the development and production of a large capital investment costs ; processing technology is more complex , requiring experienced operators and managers ; WG recipe specificity strong variation of raw materials is more complicated sense ; manufacturing process conditions are harsh , long development cycle. Currently, only a few units of WG began to grasp the technology , but it can supply the market is still very little variety and quantity , in pesticide sales market share is very low, far behind the level of developed countries , the need to increase research and development efforts, as soon as possible to catch up with developed Western countries .
