Polyurea (PU) is a distinctive polymer with a unique set of physico-chemical properties that range from abrasion resistance to water repellency to leather appearance. Along with polyurethane shells, polyurea microcapsules have been extensively studied in the past for their controlled-release applications in various industrial fields such as textiles, agriculture, cosmetics, food and medicine. Additionally, it is possible to incorporate flame retardant components to such polyureas to improve the fire behavior of the coatings and the core material. Various microencapsulation techniques have been used to obtain fine capsules or particles starting mainly from aliphatic monomers such as hexamethylene diisocyanate (HMDI) and/or ethylene-diamine (EDA). It is well known that the properties of the resultant polyurea microcapsules, such as mechanical strength, thermal stability and release rate, are strongly dependent on the chemical structure of the starting monomers and on the final size of the capsules. Furthermore, depending on the technique used to prepare the capsules, the final properties may vary significantly. A very useful and relatively easy way to encapsulate a liquid core in a polymeric shell is represented by the interfacial emulsion-polymerization method, in which the two monomers react either at the interface of aqueous and organic phases or at the interface of two immiscible oily phases.
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