Improving dirt pickup resistance in waterborne coatings using latex blends of acrylic/PDMS polymers

Abstract

Abstract Improving dirt pickup resistance especially in waterborne coatings is critical to future coating innovations. This article focuses on resins used in the coatings with the aim of enhancing dirt pick up resistance. It presents initially optimization of an acrylic (BA-St-AA) copolymer synthesized through free-radical emulsion polymerization and also, a polydimethylsiloxane (PDMS) homopolymer via cationic ring opening macro-emulsion polymerization of octamethyl cyclotetrasiloxane (D4). Concentration of monomers, Type of anionic emulsifiers, impeller stirrer speed and reaction temperature were considered as variables in order to reach a high yield of conversion and colloidal stability. The polymers were characterized using fourier transfer infrared spectroscopy, gel permeation chromatography and particle size analysis. The optimized latexes were then blended in different ratios (0/100–100/0) and the properties of the films were assessed using optical microscopy, Si-mapping EDX analysis, contact angle measurement, water up-take, and color measuremets as well as stress strain analysis. The characterization results revealed latexes with optimized conversion and uni-modal particle size distribution (PSD) were synthesized (PDMS: PSD 25–250 nm, M n 129000, PDI 2.23 and Acrylic: PSD 75–400 nm, M n 61,000, and PDI 4.95). It was found that 10–28 wt% PDMS in blends provides continuous and clear films with low dirt pickup properties. The optimized latex blend film showed a drying time of 25 min, contact angle of 96°, water uptake of 27% after 6 days, tensile strength of 7 MPa, and elongation at break of 690%. The results confirmed that blending acrylic and silicone latexes in bi-modal PSD and optimized ratios leads to a good performance exterior and uniform hydrophobic coating.