Multifunctional, Gemini-Type Coalescing Surfactants Enable Formulation of Lower VOC Waterborne Coatings

By Ernest C. Galgoci, Khalil Yacoub, Virendra V. Shah, Roger Reinartz, Kenneth A. Yoxheimer, Steven Y. Chan

Increasingly, surfactants with multifunctional performance benefits are desired to not only lower the surface tension of waterborne formulations, but also to reduce foam. Low HLB, nonionic Gemini-type surfactants are commonly utilized for this reason. As legislation has required coatings with increasingly lower volatile organic compounds (VOCs) and, consequently, lower coalescent levels, the ability of Gemini surfactants to reduce the mini­mum film formation temperature (MFFT) of emulsion polymers has gar­nered interest as a means to enable formulation of lower VOC coatings.

This article describes the MFFT reduction imparted by Gemini-type surfactants for a wide variety of emulsion polymers. Atomic force microscopy (AFM) showed that films prepared using an alkyl ester (AE) surfactant were gener­ally smoother than films not containing the AE surfactant. While enabling low-VOC formulating, these surfactants were found to have minimal effect on coating performance. Lower HLB surfactants were found to be the most effective coalescing. A simple model whereby these surfactants preferentially adsorb onto the surface of the polymer particles is introduced to explain their efficiency.

As new and more stringent VOC rules have been adopted or proposed by the South Coast Air Quality Management District (SCAQMD)1 and Ozone Transport Commission (OTC)2 for a wide range of coatings including archi­tectural and industrial maintenance (AIM), paint formulators have been evaluating new methods to reduce VOCs and yet maintain the performance of their coatings. For waterborne systems, new developments include emul­sion resins³ with lower MFFTs and low-to-no VOC coalescing agents4-6 that present the possibility to replace traditional coalescents such as the widely used 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMPIB).