Waterborne Alkyd-Acrylic Hybrids with High Solids Content -Preparation and Properties-
Sammanfattning: The work presented in this thesis concerns the preparation, characterization and film formation of a waterborne alkyd-acrylic hybrid system with high solids content of about 80 %. The alkyd-acrylic hybrids were prepared by slowly adding a linseed oil alkyd to an acrylic latex dispersion under stirring. In this work two acrylic dispersions with different glass transition temperatures were used in the hybrid preparation. Regarding characterization, the internal structure of the hybrids in the dispersion state, droplet size of the alkyd, rheology of the hybrid system, film morphology, dynamic mechanical properties, emissions from the hybrid films and other film properties such as hardness and gloss were investigated. The study of the hybrid morphologies by light microscopy showed different morphologies for the alkyd-acrylic hybrids depending on which method was used for stabilization of the alkyd droplets. Multi-emulsions (W/O/W) were observed when the alkyd droplets were stabilized by deprotonation of the alkyd phase, and when additional surfactant was added in the oil phase. An oil-in-water (O/W) emulsion was observed if the surfactant was added to the aqueous phase. The alkyd droplet size decreased with increasing surfactant concentration. In order to achieve the same alkyd droplet size lower surfactant concentration was needed if the surfactant was added to the aqueous phase. The hybrid systems exhibited a minimum in alkyd droplet size at a pH value of about 8. Concerning alkyd droplet size we performed more detailed studies and the effect of latex particles in the hybrid system and other parameters such as alkyd viscosity and solids content have been investigated. The rheological measurements of the hybrid system exhibited a shear-thinning behavior. Increasing solids content, surfactant concentration and pH increased the hybrid viscosity. Linear viscoelastic measurement revealed a dominant elastic behavior for the hybrid system with high solids content. The morphologies of the hybrid films were studied by Transmission Electron Microscopy (TEM). It was found that the morphologies of the hybrid films originated from the hybrid morphology in the dispersion form. The main difference between the dispersion and film morphologies was that a part of the alkyd phase had replaced the evaporated water. The appearance of the alkyd phase between the latex particles has been proposed to occur during film formation, mainly by an imbibition mechanism. Dynamic mechanical analysis of the hybrid system using hard latex showed two distinct glass transition temperatures, and the experimental data for this system was used for mechanical modeling. Theoretical predictions based on the interlayer model used in direct mode were successfully combined with the experimental data that resulted in relevant additional information about the complex particulate morphology of the hybrid system. Furthermore, the emissions of volatile organic compounds (VOCs) from a waterborne high solids alkyd-acrylic hybrid paint were measured in the Field and Laboratory Cell (FLEC). The result from emission tests showed that the emission factor (µg/m2 h) for the alkyd-acrylic hybrid paint was lower than the value of 10 µg/m2 h recommended by the Asthma & Allergy Society for the emission factor for paints after 4 weeks.
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