Preparation And Characterization Of Chlorpyrifos-Loaded Microcapsules

Poly (urea-formaldehyde) (PUF) microcapsules loaded with chlorpyrifos were formulated by in situ polymerization using industrial product of urea-formaldehyde adhesive. The properties of the microcapsules were characterized, the main factors affecting the properties of the microcapsules were discussed, and the conditions for preparing the microcapsules were optimized.The results showed that the drug loading, the encapsulation efficiency and the rates of controlled release of the microcapsules were remarkably affected by variations in the curing agent, the shell/core ratio and the reaction temperatures, but slightly affected by the reaction time and the rates of adding curing agent. Among the three used curing agents such as acetic acid, oxalic acid and p-toluenesulfonic acid, oxalic acid was the best curing agent for the formulation of microcapsules in terms of drug loading, encapsulation efficiency and the rates of controlled release as well. As the shell/core ratio increased, the encapsulation efficiency and the yield increased, but the drug loading decreased slightly. With an increase in the reaction temperature, the encapsulation efficiency and the yield dropped significantly, the drug loading, however, remained unchanged at the initial stage then reduced at the late stage. The reaction conditions were optimized as follows: oxalic acid used as a curing agent; the shell/core ratio of 0.94; reaction temperature of 40℃. The microcapsules formulated under this condition had the drug loading of 67.66%, the encapsulation efficiency of 87.68% and the yield of 88.23%. The microcapsules prepared at low reaction temperature in this research were comparable in properties with the microcapsules prepared by in situ polymerization using urea and formaldehyde under the equivalent formulation conditions.The SEM micrographs showed that the microcapsules prepared at low reaction temperature and low rate of adding curing agent had less rough surfaces. The FT-IR spectra indicated that there was no chemical reaction between the shell material and the core material of the microcapsules. The in vitro release results showed that, among the microcapsules prepared from PUF resin adhesive, the microcapsules prepared from urea and formaldehyde and the imported commercial product, the microcapsules prepared from PUF resin adhesive had the lowest drug release rates, and the imported commercial product had the highest drug release rates; The results of the release data fitted to the generalized model (M_t/M_∞=kt~n) indicated that the drug release was mainly controlled by Fickian diffusion.