Kaolinite-armoured polyurea microcapsules fabricated on Pickering emulsion: controllable encapsulation and release performance of a lipophilic compound

Abstract

Microcapsules are successfully used in various applications such as self-healing, drug delivery and military camouflage. The shells of the microcapsules based on the traditional surfactant-stabilized emulsion template method are often single organic materials. The surfactants generally have insufficient stability against demulsification during preparation of the microcapsules. In the present study, kaolinite was used as an emulsifier for stabilizing Pickering emulsions and subsequently as an enhancer for forming microcapsules. Kaolinite-armoured polyurea microcapsules were fabricated based on the interfacial polymerization of isophorone diisocyanate at the oil–water interfaces of kaolinite-stabilized Pickering emulsions. The prepared microcapsules with core–shell structure were spherical and exhibited good dispersibility in anhydrous ethanol. The shell thickness (~0.5–1.0 μm) and diameter (~20.0–160.0 μm) of kaolinite-armoured polyurea microcapsules may be tailored by varying the dosages of isophorone diisocyanate and kaolinite and the emulsifying speed of the high-shear homogenizer. Hence, the encapsulation and release performance of microcapsules may be controlled. The kaolinite particles were embedded and armoured in a polyurea matrix. The formed kaolinite-embedded and -armoured polyurea structures might prolong the release of the encapsulated lipophilic Sudan Red (III) from 20 to 45 h. The microcapsules have controllable encapsulation and release characteristics for lipophilic compounds and are cost effective, making them suitable pesticides.