Optimum core-shell ratio in microcapsules containing a reactive solution

The urea-formaldehyde microcapsules containing a peroxide solution were synthesized through oil-in-water emulsion. The optimum core-shell ratio was investigated by optical microscopy and scanning electron microscopy. Optimum core-shell ratio leads to a more efficient releasing and subsequently more healing ability. Five distinct core-shell ratios of 60/40, 70/30, 80/20, 90/10 and 95/5 were synthesized. It was suggested that the core-shell ratio of 90/10 produced the most spherical microcapsules without shell wrinkles. Microcapsules less than the above-mentioned core-shell ratio suffered from a thick layer of porous UF on the surface which results in agglomeration of microcapsules and consequently less stability. The attempt to synthesize microcapsules with core-shell ratio of 95/5 led to very unstable microcapsules with such a thin UF shell that released after filtration. The optimum core-shell content was chosen by optical microscopy and scanning electron microscopy and the core content of 90 percent was confirmed by thermo gravimetric analysis (TGA )