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Encapsulation de pigments aluminium par un revêtement polymère pour une application peinture poudre

Abstract : The high increase of powder coating market induce development of new compatible fillers, and especially
specific aluminium pigment grades to obtain high metallic effects. Therefore, polymer encapsulation of
pigments appears as a good strategy.
In this study, a new simple and envirommentally-friendly process in aqueous media is developed by the use of peroxodisulfate ions. First, these anions inhibit the aluminium corrosion by passivation, and then, they
initiate the methacrylates polymerisation. Particles agglomeration limitation and uniform polymer layer
formation, which result in optimal optic effects, are obtained by specific reaction conditions.
Concerning peroxodisulfate and aluminium interactions, an oxidation reaction has been identified. Optimal
conditions have been found on a specific aluminium pigment grade and an interaction mechanism has been
proposed to explain passivation at low rate and complete oxidation at larger rate, observed by gassing tests,
pH evolution and scanning electron microscopy. To disperse aluminium pigments in water, paste solvent (white spirit) is exchanged by water-miscible
solvent. Polymerisation rate determination, laser granulometry evolution, SEM micrographs and
chromatography analysis enabled us to distinguish different steps during the encapsulation process. The first, long, step is characterized by polymer particles formation and adsorption on the aluminium surface. Then, the polymer particles grow at the surface until their coalescence forming a film. Therefore specific reactants and conditions have been used as a specific surfactant, a sequential or continuous persulfate solution addition, a monomer mixture containing principally methyl methacrylate for its hydrosolubility and a small amount of hydrophobic monomer to increase film-forming ability.
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Nicolas Doreau. Encapsulation de pigments aluminium par un revêtement polymère pour une application peinture poudre. Matériaux. Université Sciences et Technologies - Bordeaux I, 2005. Français. ⟨tel-00129354⟩

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