Direct Preparation Process of Microcapsules by in situ Polymerization of Urea-Formaldehyde

s: Microcapsules containing an organic solvent as an internal phase were prepared by the in situ polymerization of urea-formaldehyde without prepolymerization. The influences of system modifiers, pH value, and reaction time on the process of microencapsulation and the morphology of the microcapsules were investigated. When the microencapsulation is conducted in a system modified by PVA and with a pH value of 2.5 or lower, the microcapsule shells have good smoothness but less strength. When the system modifier is PAA and the pH value is 3.5, the shells of the microcapsules are of good smoothness, transparency and strength. The process of direct preparation of microcapsules by in situ polymerization of urea-formaldehyde was analyzed. It is shown that the interfacial behavior of the phases in the system plays an important role in the process of microencapsulation, and a slow and sufficient liquid/liquid phase separation effected by an appropriate system modifier under appropriate conditions is necessary for producing microcapsules of good morphology and mechanical strength.