Preparation And Study Of Suspension Concentrate Of Microspheres Of Chlorpyrifos And Polylactic Acid

Based on biodegradable polylactic acid (PLA) as wall materials and chlorpyrifos as core materials, the sustained-release microspheres of chlorpyrifos was studied by using solvent evaporation method. The effects of emulsifying equipment, organic solvent, reaction temperature, stirring velocity, O/W ratio, ratio between core materials and wall materials (chlorpyrifos weight/PLA weight, CP value) and concentration of PLA on the characteristics of microsphere were investigated. Furthermore, the microspheres were tested by the differential scanning calorimetry (DSC) and the drug release properties were investigated. The result showed that the optimistic quality could be achieved while the cut inside type the distributor as the emulsifying equipment, methylene chloride as the organic solvent, the mixture of polyvinyl alcohol and gelatin as the emulsifier and reaction temperature at25℃-35℃. Along with the acceleration of emulsification, the diameter of microspheres increased after initial decreased. As O/W ratio increased, the diameter of microspheres declined. While the concentration of emulsifier increased, the diameter declined and the drug-loading rate and entrapment rate of microspheres was greater in the proportion of1.0%and1.5%.The concentration of PLA increased would induce the diameter and the drug-loading rate and the entrapment rate of microspheres increased. As the ratio between core materials and wall materials (chlorpyrifos weight/PLA weight, CP value) decreased, the diameter and the drug-loading rate of microspheres reduced, but the entrapment rate of microspheres were89.88%±1.67%and90.55%±1.86%in the condition of1:3and1:4. While ratio between core materials and wall materials (chlorpyrifos weight/PLA weight, CP value) was lower than1:2, the surface of microspheres was smooth. The differential scanning calorimetry (DSC) determination indicated that chlorpyrifos and PLA were combined well in the microspheres of chlorpyrifos. The result of drug release properties of chlorpyrifos/PLA microspheres indicated that the significant sustained-release ability were possessed by microspheres prepared.The chlorpyrifos/PLA microspheres were prepared with the better technological parameter. Besides, the effect of wetting dispersants, thickening agent, and the anti-freeze agent to microspheres SC was investigated. The results showed that the best quality of the chlorpyrifos/PLA microspheres SC was produced with proportion of wetting dispersants (A and B)2.5%and2.5%, the thickening agent(Magnesium silicate aluminum)3.5%and anti-freeze agent(glycol)5%, respectively.The toxicity of chlorpyrifos/PLA microspheres SC to the larva of Plutella xylostella was evaluated. The48%chlorpyrifos EC was used to evaluate comparative toxicity. The result showed that LC50(474.796mg/L) of the chlorpyrifos/PLA microspheres SC was higher than LC50(248.715mg/L) of chlorpyrifos EC which was probably caused by the incomplete release of chlorpyrifos/PLA microspheres.