Effect of particle morphology on film morphology and properties
Limousin, Elodie Aurore
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The main goal of this PhD thesis was to establish a link between particle morphology and film morphology in hybrid particles latexes. The strategy used to understand it was to study the film morphology and properties of a variety of polymer-polymer hybrid particles latexes. For each system studied, different morphologies with near identical compositions and polymer microstructure were prepared. We demonstrated that film morphology is directly influenced by the particle morphology. Core-shell morphologies led to a honeycomb structure with a MFFT close to the Tg of the soft polymer. Hemispherical morphologies led to the formation of small aggregates of hard polymers in the soft matrix during film formation, which increases the MFFT of the film. Particles containing a hard polymer on the outer part of the particles allowed film formation close to room temperature. Tensile tests were performed for all the systems studied. The honeycomb-like structure displayed by films cast from soft core-hard shell particles enhances the film stiffness as the continuous phase is formed of the hard polymer. When the continuous phase is soft, the hard polymer is dispersed the soft continuous phase, the film is reinforced compared to a pure soft film. Hemispherical morphologies led to higher film stiffness than hard core-soft shell ones. Indeed, the formation of small aggregates of hard polymers increases the film. We demonstrated by thermal treatment of the films that the film morphology strongly affects the properties of the film. Thermal treatment above the Tg of the hard phase encourage phase migration and the polymers segregate or form a co-continuous structure if the compatibility of the polymers was high. Indeed, we showed that, in addition to the particle morphology, the compatibility between the phases has to be taken in account for film formation. If the phases show low compatibility they segregate during film formation. In order to confirm the advantages of hybrid particles to the use of blends, we compared hybrid particles latexes with a blend of two latexes of same overall compositions. We confirmed that hybrid particles lead to more homogeneous films structure. The latexes were used as binder in coatings applications. It was observed that the morphologies of the paint films from acrylic / alkyd hybrid particles latexes were in agreement with the latexes films. Moreover, the trends shown in the properties of the formulated paints were similar to that of the latexes films. Overall, it can be concluded that the final properties of polymer films and coatings can be tailored in the reactor by carefully designed synthesis of hybrid latex particles and post-synthesis through thermal treatment of the dry polymer films.