Preparation and characterization of polyurea microcapsules with different diamines

Polyurea microcapsules were prepared by emulsion polymerization by pouring an aqueous solution with poly(vinyl alcohol) (PVA) as stabilizing agent into an organic solution with migrin oil as core material, 1,4-diamino anthraquinone (DAA) as penetrator, one of three different compositions of ethylene diamine (EDA) and 1,6-hexane diamine (HDA), and 2,4-toluene diisocyanate (TDI) as wall material. The effects of diamine type on structure, thermal properties, particle size distribution, morphologies, loading content, and release behavior of core materials of the resulting microcapsules were investigated. EDA-based polyurea microcapsules had a wider particle size distribution and a much rougher surface compared with the HDA-based microcapsules. Loading content of the penetrator (DAA) in the EDA-based samples also was higher, due to rapid wall-forming by EDA, but the release rate was lower due to their greater wall thickness. The release rate seems to be related to wall thickness of the microcapsules from different compositions, irrespective of the size of emulsion globules. (C) 1999 Elsevier Science Ltd.