Hydrophobic core/shell particles via miniemulsion polymerization
Date
2006-12
Authors
Etmimi, Hussein Mohamed
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
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.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
Keywords
Polymerization, Addition polymerization, Dissertations -- Polymer science, Theses -- Polymer science