Preparation Of Trifluralin Microcapsules And Research Of Their Delivery Performances

Pesticide was a double-edged sword, which played an important role in pest control but also caused problems such as pesticide residue, increasing expose risk of administers and non-target organisms poisoning. The basic reason of the problems was the low effective utilization of pesticide. Photolysis was the main reason of the low effective utilization of photo-sensitive pesticide. Trifluralin was a kind of photo-sensitive pesticide and its photolysis products were mostly non-bioactivity. With trifluralin as the model drug, photo-sensitive pestic ide-loaded controlled release systems were established using microencapsulation and their delivery performances were studied in order to explore a feasible technical way to improve effective utilization of pesticide.Firstly, two kinds of trifluralin- loaded controlled release systems were set up using microencapsulation followed by characterization. With methyl methacrylate(MMA) and natural polymer chatoyant(CS) as wall mater ials, the chitosan-poly(methyl methacrylate)-trifluralin(CS-PMMA-TF) microcapsules were prepared by in-situ polymerization method. The microcapsules were well-defined yellow spherical particles with average size 6.5 μm and encapsulation efficiency(EE) 78.9 % and loading content(LC) 45.4 %. Using EE and LC as evaluation standards, the preparation conditions were optimized by single factor test, which were the initiator ammonium cerium nitrate 0.18 g, the mass ratio of chitosan to methyl methacrylate 1:2, the mass ratio of trifluralin technical to wall materials 1:5. With biodegradable synthetic polymer polyhydroxybutyrate(PHB) as wall mater ial, the polyhydroxybutyrate-trifluralin(PHB-TF) microcapsules were prepared by emulsion solvent evaporation method. The microcapsules were well-defined yellow spherical particles with average size 2.5 μm and EE 83.5 % and LC 16.4 %. The effect of the mass ratio of TF to PHB, the volume ratio of oil phase to aqueous phase, the mass fraction of Polyvinyl alcohol(P VA) and stirring speed on the average size, EE and LC of the PHB-TF microcapsules suggested that the average size(D32) signif icantly decreased as the stirring speed and the mass fraction of PVA increased. The linear relationship between average size(D32) and stirring speed(N) was ln D32 = 5.5586-0.4896 ln N(R2 = 0.9958). Therefore, the size could be decreased by increasing the mass fraction of PVA and the stirring speed. The the mass fraction of PVA must be ensured as too little PVA causing unstable microcapsules. The EE and LC could be enhanced with increasing the mass ratio of TF to PHB. Us ing EE and LC as evaluation standards, the preparation conditions were optimized by orthogonal test, which were the mass ratio of TF to PHB 1:5, the volume ratio of oil phase to aqueous phase 1:5, the mass fraction of PVA 1 % and stirring speed 12000r/min. Microcapsules with good performances could be prepared by adjusting the preparation conditions, which was of great significance for improving the effective utilization.Secondly, the sustained release performances of CS-PMMA-TF microcapsules and PHB-TF microcapsules were researched by leaching method and dialysis method, respectively. The results suggested that these two trifluralin- loaded microcapsules both had good sustained release performances. The release performance of CS-PMMA-TF microcapsules was controlled mainly by Fick diffusion. The release of PHB-TF microcapsules speeded up as the stirring speed and the mass fraction of PVA increased and the microcapsules’ release followed Fick’s second law. The study of microcapsules release mechanism could provide scientific basis for controlling release rate and formulating the application dose of pesticide microcapsules.Lastly, the study of photo-stability of two kinds of trifluralin- loaded microcapsules showed that the photolysis rate of trifluralin-loaded microcapsules under UV- light or in soil or in water were all signif icantly reduced than that of emulsifiable concentrate. The photo-stability of trifluralin- loaded microcapsules was enhanced, which was of great importance for improving the effective utilization.In this paper, the in-situ polymerization method and emulsion solvent evaporation method were first used to prepare trifluralin- loaded microcapsules. Two kinds of trifluralin-loaded microcapsules were all well-defined yellow spherical particles with uniform size and high EE and LC, which lay the foundation for improving the effective utilization of trifluralin. The wall mater ials used was t he biocompatible and biodegradable CS and PHB, avoiding the pollution to environment. The microcapsules with the best size and high EE and LC could be prepared by adjusting preparation conditions. The good sustained release and photo-stability were significantly important to enhance the effective utilization of pesticide.