Microencapsulation in polyurea shell by interfacial polycondensation

Abstract

A 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 rneasurement 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 prn can be produced, and the surface to volume mean size varies only from 2 to 6 pm 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.

An experimental study of polyurea membrane formation by interfacial polycondensation

“…The reaction, since it employs highly reactive monomers, is extremely fast and this poses problems in measurement of rates. Yadav et al in their studies on microencapsulation in polyurea shells devised a simple on-line pH measurement technique for following the process kinetics [8,9]. Their work demonstrated the potential of the technique in following fast kinetics in a system of this kind, but the potential could not be fully realized because of the discrete nature of the measurement.…”

“…In some experiments, sodium lignosulfonate (instead of Tween-85) was used as the surfactant since it was found that microcapsules thus formed were better able to maintain their shape under the sample preparation procedures used for electron microscopy. The experimental procedure followed for the preparation of polyurea microcapsules was in general similar to that reported earlier [8,9]. A two-step procedure was adopted to ensure that the drop size distribution was the same in all the experiments.…”

“…1 shows a typical calibration plot. In earlier work [8,9], we had compared such experimental calibrations with the theoretically derived relation between pH and concentrations for pure HMDA solutions, and shown that over the range of experimental interest, the relationship is satisfactorily expressed by an equation of the form:…”

Interfacial polycondensation—Modeling of kinetics and film properties

“…Experimental evidence [3,5,6,11,[18][19][20][21] points to a strong influence of the conditions employed in the preparation on the nature and properties of the film that forms. However, most of the models [7][8][9][10][11][14][15][16][17] focus on the kinetics and the variation of film thickness with time, and do not attempt to predict quantitatively the polymer properties as a function of process parameters. Properties such as molecular weight, polydispersity and crystallinity affect important characteristics of the polymer [20][21][22] such as mechanical properties, viscosity, ease of processing, permeability.…”

Review on microencapsulated phase change materials (MEPCMs): Fabrication, characterization and applications

“…Yadav et al [42] carried out an early theoretical study on the microencapsulation of butachlor in polyurea shell by interfacial polymerization. They concluded that the time of encapsulation depended on the size of the microcapsule and by monitoring the pH of the continuous phase, and the capsule size was weakly dependent on the rpm.…”