Revêtements nanocomposites UV-Aqueux pour le bois à usage intérieur

Authors: Sow, Caroline
Advisor: Riedl, BernardBlanchet, Pierre
Abstract: This research aimed to study the effect of alumina and silica nanoparticles on the properties of varnishes type UV-waterborne nanocomposite coatings for wood products. Mechanical (abrasion resistance, hardness, scratch resistance, impact resistance and adhesion), optical (gloss and color) and thermal (thermal stability and glass transition temperature) properties were analyzed and compared to those of the neat varnish containing no nanoparticles. Not only was the scratch resistance improved following the addition of nanoparticles but also the adhesion of nanocomposite varnishes. However, the presence of nanoparticle aggregates as suggested by transmission electron microscopy (TEM) led to a decrease of the abrasion resistance, the hardness and the impact resistance. As expected, the gloss of varnishes was reduced because of the presence of aggregates which increase the surface roughness of nanocomposite varnishes, although color properties remained unchanged in terms of lighting and yellowing. Ultrasonication was shown to be an efficient dispersion method. Not only did the size of aggregates decrease following the dispersion of nanoalumina and nanosilica in polyurethane-acrylate (PUA) by means of ultrasounds but also their number. Moreover, the improvement of nanoparticle dispersion led to improve the hardness and the impact resistance of nanocomposite varnishes in comparison to varnishes based on nanoparticles dispersed with high speed mixer. Also, ultrasonication presents some disadvantage as thermal properties have demonstrated that ultrasounds could affect PUA resin. Curing kinetic study by means of photodifferential scanning calorimetry (photo-DSC) demonstrated two interesting advantages of UV-waterborne coatings: UV-curing is very fast as the reaction is achieved after 18s and contrary to high solid content UV-coatings, photopolymerization is insensitive to oxygen in spite of free-radical formation during the reaction. The decrease of exothermic curves, obtained from photo-DSC, revealed that the addition of nanoparticles reduced the photopolymerization efficiency of nanocomposite varnishes. Finally, it has been demonstrated that the kinetic profile of nanocomposite varnishes could be described using an autocatalytic model. The importance of surface modification was demonstrated with the study of nanosilica behavior. Not only did the amount and the size of nanosilica aggregates decrease following grafting methacryloxypropyltrimethoxysilane (MEMO) groups on the surface of silica nanoparticles but also the number of reactive acrylates functions which can take part in the free-radical polymerization. As a result, the dispersion of silica nanoparticles was better than the one of alumina nanoparticles and nanocomposite varnishes containing nanosilica presented better properties in comparison to nanocomposite varnishes containing nanoalumina dispersed with high speed mixer.
Document Type: Thèse de doctorat
Issue Date: 2010
Open Access Date: 16 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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