RPM Variation Research Articles

Microencapsulation in polyurea shell by interfacial polycondensation

AbstractA model and a simple measurement technique for time of encapsulation have been developed to study the microencapsulation of butachlor in polyurea shell by means of interfacial polymerization. The model is based on diffusion of the hydrophilic monomer through the polymeric shell with an interfacial reaction at the inner surface while the measurement technique is based on the indirect determination of the concentration of the hydrophilic monomer in the continuous phase by monitoring the pH. Measurements show that capsule sizes ranging from 1 to 20 μm can be produced, and the surface to volume mean size varies only from 2 to 6 μm for a large variation in rpm of the agitator. Time of encapsulation is found to be approximately proportional to the microcapsule size, and it varies from 150 to 300 s. Both the data and the model were used to discern that the process is kinetically‐controlled by and large. It is also shown that time of encapsulation varies with the square of the capsule size in a diffusion‐controlled regime.