Characterization and reduction of leakiness in melamine formaldehyde microcapsules

Abstract

This thesis is concerned with tackling three major challenges of melamine formaldehyde (MF) microcapsules for delivering of core materials: reducing the formaldehyde content in the formulation, modulate the mechanical properties and reducing the leakage of the core material through the microcapsules.
Thus, to reduce the formaldehyde content in the microcapsules, a low formaldehyde to melamine (F/M) molar ratio (0.20-0.49) compared to the conventional literature formulations (2.30-5.50) was used to produce the MF microcapsules in this study. It was found that there is a relatively small window of F/M molar ratio between 0.20 and 0.49 in which the wall thickness and nominal rupture stress of the microcapsules can be modulated significantly. Above 0.49 increases in F/M molar ratios only increase these properties marginally.
Furthermore, to reduce the leakage of the microcapsules, organic/inorganic double shell composite microcapsules with MF/copolymer as the inner shell, and ripened CaCO\(_3\) nanoparticles as the outer shell were produced. A ~20 fold reduction in leakage was observed between the double shell composite microcapsules and the MF microcapsules by the end of 24 hours, and it was also found that the mechanical properties of these double shell composite microcapsules are dominated by the CaCO\(_3\) nanoparticles outer wall.
Finally, calcium shellac matrix containing MF microcapsules and unripened CaCO\(_3\) nanoparticulate microcapsules (complex capsules) were also produced to reduce the leakage. A ~37 fold leakage reduction between calcium shellac matrix containing MF microcapsules and MF microcapsules alone by the end of 20 days was observed, and a ~14 fold reduction was found between calcium shellac containing unripened CaCO3 nanoparticulate microcapsules and the unripened CaCO\(_3\) nanoparticulate microcapsules alone.