Effect Of Surfactant And Thickening Agent On Physical Stability Of Storage Of Flowable Concentrate For Seed Coating

Bleeding, thickening and sedimentation caused by aggregation and recrystallization of pesticide particles have been serious problems for physical stability of some flowable concentrates for seed coating (FSC) during storage. Characters of 20% thiram-carbofuran FSC and 30% carbendasimthiram-carbofuran FSC along with concentrations of surfactants and thickening agents have been detected, including viscosity, supernatant-sediment ratio, particle aggregation, and unrecoverable sedimentation. Moreover, high performance liquid chromatography (HPLC) was applied to analyse adsorption of Witconol NP-100, a nonionic surfactant, on pesticide particles as well as the amount of pesticide ingredients dissolved. Effects of other agents including Morwet D-425, an anionic surfactant, and bentonite together with storage temperature on the adsorption of Witconol NP-100 have also been studied. The paper preliminarily studied the mechanism of surfactants and thickening agents improving storage physical stability of FSC and obtained some results.The data showed that particle aggregation and viscosity of the FSCs have been greatly reduced with the concentration of Witconol NP-100 and Morwet D-425 increased. XG powders cooperated with bentonite can greatly affect the level and stability of viscosity as well as decrease sedimentation. When Morwet D-425 and Witconol NP-100 respectively was used at the concentration of 10g/L and 30g/L in 20% thiram-carbofuran FSC with 3g/L XG powders and 15g/L 4# bentonite in it, or 10g/L and 40g/L in 30% carbendasinvthiranvcarbofuran FSC with 1.7g/L XG powders and 15.0g/L 4# bentonite, supernatant-sediment ratio of the FSC get to the minimum of 5% and 9% after 14 days of storage under the condition of (54?)癈. Viscosity was 390 mP s and 510 mP s and particle aggregated less than 10%. No unrecoverable sedimentation emerged in the experiment conditions.HPLC detection showed that Witconol NP-100 adsorption isotherm on thiram and carbofuran is Langmuir type. The saturation adsorption of Witconol NP-100 on pesticide particles decreased with concentration of Morwet D-425 improved and increased in circumstance of higher storage temperature. It is the adsorbing of Bentonite that added the maximum adsorption and improved the need of Witconol NP-100 to 7.3g/L. Morwet D-425 and Witconol NP-100 both showed ability to enhance dissolution of thiram and carbofuran. Higher temperature can help as well.Consequently, from what has discussed above we can draw some conclusions. Surfactant plays an important role in physical stability of FSC, reducing viscosity and dispersing pesticide particles. If less surfactant was used, part but not all the surface of pesticide particles will be covered. Attraction between particles will cause aggregation and liquid bleeding. If surfactant is enough to form acontinuance layer outside pesticide particles, another reason--viscosity reduction will explain theaggregation of particles. Accordingly, the character of bleeding is determined by formulation viscosity, particle diameter, dispersion degree and other aspects. Can a stabile FSC be obtained only through a good cooperation of surfactant and thickening agent.