Preparation And Release Property Of Melamine Resin/ Polyvinyl Alcohol Dual-encapsuled Microcapsule Essence

With type 71111 lemon essence as core material, Arabia gum as dispersant, melamine resin and polyvinyl alcohol compound as the first and the second layer of shell materials, a kind of microencapsulated essence powder products has been prepared by in situ polymerization method.Through analytical tests including electron microscope, granulometer and thermogravimetric analyzer, some reaction conditions were investigated such as effects of dispersant dosage, reaction temperature and time for melamine resin, reaction pH, core/wall ratio, amine aldehyde ratio, speed and time of stirring on how they affect the particle size and morphology, encapsulation efficiency, sustained release property and heat resistance of microcapsules.The results show that the appropriate particle size for essence drops can be obtained by using Arabic gum as dispersing agent with emulsifying at 2000r/min under 50℃ for 20min. In the period of prepolymerization, the molar ratio of melamine and formaldehyde is 1:3, pH controlled at 8.5-9.0, temperature controlled at 70℃, and add a small amount of gelatin to modify the resins. Mix the prepolymer and essence emulsion, then pH controled at 4.8 and react 200min under 48℃ and hold another 180min under 65℃ to obtain melamine resin microcapsule.Chose polyvinyl alcohol-aldehyde compound as the second shell material, which greatly improved the tightness and release stability of microcapsule and also preserved good compatibility with melamine resins. Polyvinyl alcohol with low molecular weight will cause products hard to separate, and also hard to participate in reaction if the molecular weight is too high, so PVA2699 is the most appropriate choice. Use 80% of melamine’s mass as amount of PVA with a appropriate amount of glutaraldehyde and formaldehyde, then with pH controled at 3.5 under 48℃, react at least 240min to obtain polyvinyl alcohol composite wall material.After reaction, add urea to removal remained formaldehyde and wash products with deionized water and ethanol to get essence microcapsule products with essence content about 34%, yield about 80% and covering ratio 40%.