Morphology and structure of microcapsules prepared by interfacial polycondensation of methylene bis(phenyl isocyanate) with hexamethylene diamine

Abstract

Polyurea microcapsules containing 2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide as the active agent were prepared by the method of interfacial polycondensation with methylene bis(phenyl isocyanate) as the multifunctional isocyanate, hexamethylene diamine as the diamine, and anionic sodium lignin sulphonate (SLS) as the emulsifying agent. The internal structure and morphology of the microcapsules were examined with transmission electron microscopy. The microcapsules had a micro-reservoir structure in which the wall extended well into the core and the active agent was accommodated by the micro-reservoirs, distributed uniformly throughout the entire volume of a microcapsule. Based on the observed morphology, permeability of the water soluble monomer in the polyurea film and its solubility in the oil phase have a significant effect on the morphology and microstructure of the microcapsules. The multivalent salt, calcium chloride, plays a significant role in stabilizing the microcapsule structure, by interacting with the anionic surfactant SLS, and physically crosslinks the SLS chains, by interacting with the negatively charged carboxylic and phenolic groups, with subsequent phase separation of the physically crosslinked chains to form a concentrated gel phase. This gel phase encompasses the microcapsule, increases the stability, and modifies its release behaviour.