Impact of EO chain length of dodecanol ethoxylates (C12En) on the rheological properties and physical stability of pesticide suspension concentrate

Rheological measurement can provide not only the shear-induced but also strain-induced microstructural changes, as well as transient network formation and subsequent recovery with time. It has been explored as a useful tool for probing the interparticle interactions which govern the physical stability of concentrated suspension. However, its application in pesticide formulation is rarely investigated. Herein, the rheological properties of 25% mancozeb suspension concentrate stabilized with nonionic surfactants dodecanol ethoxylates (C 12 E n , n = 3, 7, 9, 15, 20) were studied. The steady-state shear measurement showed that all the 25% mancozeb suspension concentrate displayed shear-thinning flow. The experimental flow behavior followed prediction of Herschel–Bulkley model with the correlation coefficients greater than 0.99. Oscillatory shear measurements showed the viscoelastic response of 25% mancozeb suspension concentrate transformed from solid-like to gel-like viscoelasticity with the addition of C 12 E n . As the EO chain length of C 12 E n increased, the apparent viscosity and elastic modulus decreased initially, followed by an increase behavior. The thixotropic response of mancozeb formulations was evaluated by applying a three-step test. It turned out that the addition of C 12 E n changed the mancozeb suspension concentrate from normal viscoelastic fluid to inelastic thixotropic material, and the recovery of viscosity gradually decreased as the EO chain length increased. Besides, the influence of C 12 E n on suspension rate and particle size of 25% mancozeb suspension concentrate was investigated. The results showed that C 12 E 9 performed best in improving the physical stability of the formulations before and after thermal storage. From SEM imagines of mancozeb particles, it was found that the aggregation was inhibited by C 12 E 9 , which was also responsible for the best dispersibility, minimum apparent viscosity and elastic modulus of 25% mancozeb suspension concentrate with the addition of C 12 E 9 .