Mechanism of Microencapsulation with Urea-Formaldehyde Polymer

Problem statement: Microcapsule is one of important fine chemical products in the current chemical industries. Better understanding of microencapsulation process is useful to properly design of microcapsule with specific characteristics. The aim of this research is to study the mechanism of Urea-Formaldehyde (UF) microcapsules formation. Approach: Microcapsule was prepared in two steps. The first step was the preparation of oil in water emulsion, which was carried out by mixing of UF pre-polymer solution with refined palm oil at 50-70°C, using high speed homogenizer. The second step was microcapsule shell formation, where the pH of emulsion was adjusted to 3 and the process was run for 3-6 h. At the end of the process, the microcapsule product was cooled with ice and distilled water, filtered, washed and finally dried at 40°C under vacuum condition. The diameter and size distribution of the microcapsule product was measured using optical microscope. Results: Microcapsule with the diameter of 20-220 µm, together with UF micro particles. Conclusion: UF polymerization reaction took place simultaneously in the solution and at the microcapsule surface. UF reaction in the solution produced UF polymer micro particles, while UF reaction at the microcapsule surface forms microcapsule shell. The UF polymer micro particles precipitated in the form of fine powder, attach to the microcapsule shell. Higher microencapsulation temperature reduced the amount of microcapsule product and increased the amount of micro particles. The microcapsule diameter distribution shifts to smaller diameter and the average diameter D_avg tends to decrease as the homogenization and microencapsulation time increase. Based on oil and resin efficiencies as well as microcapsule characteristics, the process is best conducted at 50°C, 30 min of homogenization and 3 h of microencapsulation time.