Enhancing durability of acrylic latex-based paints with reactive surfactants

 
Low water resistance significantly contributes to the poor durability of waterborne coatings, limiting their application in more demanding environments. Conversely, enhancing the durability of these coatings is crucial for reducing their environmental impact and promoting the development of more sustainable solutions. Optimizing the content of free water-soluble species, particularly surfactants, in waterborne formulations and ensuring good film formation are key factors for enhancing the water resistance of waterborne coatings. This study is part of a continuous effort for enhancing the water resistance of waterborne coatings and explores the partial replacement of a conventional anionic surfactant with a new reactive nonionic surfactant in the emulsion polymerization of an all-acrylic latex for exterior paints, as well as the evaluation of the morphology of the resulting latex films. The reactive nonionic surfactant molecule investigated in this work was designed to react with key monomers used in emulsion polymerization and to exhibit surface activity similar to conventional nonionic surfactants. The all-acrylic latex developed in this work was polymerized through a multi-stage process using an optimized ratio and content of conventional anionic and reactive nonionic surfactants. Its properties were compared to a standard all-acrylic latex polymerized solely with the conventional anionic surfactant. The all-acrylic latex polymerized with the optimized ratio of conventional anionic and reactive nonionic surfactants demonstrated low coagulum formation in the reactor, a particle size close to 100 nm, and a solid content of approximately 47 wt%. The incorporation of the reactive nonionic surfactant into the latex particles was nearly 100 wt%, based on HLPC evaluation of the latex serum. Additionally, this latex exhibited higher mechanical stability compared to the standard latex, reducing the coagulum formed during the mechanical stability test by almost 100 wt%. The AFM micrographs of both latexes coalesced with a zero VOC biobased coalescent show that it is possible to distinguish the particles domains within the films despite those films being very smooth with average roughness close to 1 nm. This morphology is similar to the one previously observed for commercial all-acrylic latexes. Latex films polymerized with the optimized composition of conventional anionic and reactive nonionic surfactants coalesced with the zero VOC biobased coalescent absorbed about 80 wt% less water than the standard latex. Low PVC colored paint formulated with the latex polymerized with the optimized ratio of conventional anionic and reactive nonionic surfactants exhibited lower exudation of surfactants to water, as assessed through surface tension, compared to the standard latex.