Hydrophobic core/shell particles via miniemulsion polymerization
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
Hydrophobic core/shell latex particles were synthesized for use in barrier coatings using the miniemulsion polymerization process. Particles with liquid or with hard cores were successfully synthesized using miniemulsion as a one-step nanoencapsulation technique. Different materials, including an oil (hexadecane, HD) and two different waxes (paraffin and microcrystalline wax), were used as the core of the particles. The shell of the particles was mainly made from a copolymer containing three relatively hydrophobic monomers, namely methyl methacrylate (MMA), butyl acrylate (BA) and vinyl neodecanoate (Veova-10). Before any further investigations could be carried out, it was important to determine the morphology of the synthesized core/shell particles at the nanometer level. Particle morphology was mainly determined by two different techniques: transmission electron microscopy (TEM) and atomic force microscopy (AFM). TEM was used to directly visualize the morphology of the investigated core/shell particles at the nanometer level, while AFM was used to confirm the formation of these core/shell particles. AFM was a powerful technique with which to study the particle morphology of the core/shell latices during the film formation process. As a second part of the study, the effect of various factors on the hydrophobicity and barrier properties of the resulting films produced from the synthesized core/shell latices to water and water vapour was investigated. This included the effect of: (i) the surfactant concentration, (ii) the wax/polymer ratio for both waxes, (iii) the molecular weight of the polymeric shell, (iv) the amount of the most hydrophobic monomer used (Veova-10), and (v) the degree of crosslinking in the polymeric shell. Results showed that all the above-mentioned factors had a significant impact on the water sensitivity of the resultant films prepared from the synthesized core/shell latices. It was found that the presence of wax materials as the cosurfactant, instead of HD, in the miniemulsion formulation could significantly improve the hydrophobicity and barrier properties of the final films to water and water vapour. In addition, increasing the amount of wax, Veova-10, and the molecular weight of the resultant polymeric shell, led to a significant increase in the hydrophobicity and barrier properties of the resultant latex films. In contrast, hydrophobicity and water barrier properties decreased drastically as the quantity of surfactant and degree of crosslinking increased in the final latex films.