Waterborne paints have been used in the decorative business for many years. In this technology the polymer phase, known as latex, is composed of high molecular weight polymer particles dispersed in water and stabilized by surfactants obtained by emulsion polymerization of acrylic and vinyl monomers. During drying of paint, these latex particles need to coalesce and form a uniform film, requiring the use of coalescing agents. There is currently a growing demand for coalescing agents that are considered low-VOCs (Volatile Organic Compounds), and that can also offer high performance properties like dirt pick-up resistance, reduced blocking, and low-leaching. To express this commitment, Oxiteno has developed the coalescent ULTRAFILM® 5000, which aims to meet these market demands, due to it´s high interaction with the latex polymer.
Usually, low-VOC waterborne paints generate dry paint films with lower hardness and dirt pick-up resistance due to the usage of high-boiling-point coalescents. This is not the case of the new coalescing agent developed by Oxiteno. In this work, the effect of the low-VOC coalescents on latex film formation, hardness evolution, accelerated dirt pick-up resistance, and surfactant leaching of waterborne paints is explored and compared to traditional market coalescents. An interesting form of viewing film formation is by Using AFM (atomic force microscopy) images. The images of styrene-acrylic and pure acrylic latexes containing 4 wt% of different coalescents show that low-VOC coalescents generated films that were more coalesced and smoother than standard high-VOC coalescent. The new low-VOC coalescent generated semigloss paints with higher hardness evolution and better dirt pick-up resistance than commercial low-VOC coalescents and similar to standard high-VOC coalescent. Moreover, leaching phenomena is addressed by evaluating flat paints formulated with this low-VOC coalescent dried at harsh conditions presented lower surfactant leaching in comparison to the ones formulated with standard high-VOC coalescent. These results suggest that there is a correlation between surfactant leaching and film formation assessed through AFM.
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Marina Chieregati Passarelli received her bachelor´s degree in Chemistry at the Federal University of São Carlos (UFSCar), in São Paulo. She is the author of many papers including one chapter in a coatings technical book, published in Brazil, comprehending wetting agents for waterborne formulations. Nowadays, she is pursuing a master's degree in Mining and Petroleum Engineering at the University of São Paulo (Poli-USP), and is responsible for technical support in Formulation of Architectural Paints for the Coatings market at Oxiteno.
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