Oil-acrylic hybrid latexes as binders for waterborne coatings

The combination of the characteristics of oil, or alkyd, emulsions and acrylic latexes in a waterborne binder has been the object of various studies in the past. Strategies for combining the positive properties of alkyds, e.g. autoxidative curing, gloss and penetration in wood, with the fast drying and gloss and color retention properties of acrylic latexes have mainly been directed towards the modification of the alkyd with an acrylate during alkyd synthesis followed by emulsification. This paper describes the preparation and application of oil-acrylic hybrid latexes as binders for waterborne coatings. The hybrid latexes were prepared using hydroperoxidized triglycerides as initiators for the mini-emulsion polymerization of acrylates in an Fe(II)/EDTA/SFS redox system. The particle morphology of hybrids initiated by fatty-acid hydroperoxides was compared with tert-butyl hydroperoxide-initiated systems. Cryo-TEM analysis indicated that, whereas tert-butyl hydroperoxide initiation resulted in the formation of heterogeneous particles, fatty-acid hydroperoxide-initiated hybrid particles showed no intra-particle heterogeneity. An AFM study of the film formation process of the oil/alkyd-acrylic hybrid latexes showed that phase separation occurred between the oil and the acrylic phases upon drying, resulting in films that consist of deformed acrylic particles embedded in a continuous matrix of oil. This results in a very smooth surface of the film.