Improving the dirt pickup resistance in water-borne coatings

It presents initially optimisation of an acrylic (BA-St-AA) copolymer synthesised through free-radical emulsion polymerisation and also, a polydimethylsiloxane (PDMS) homopolymer via cationic ring opening macro-emulsion polymerisation of octamethyl cyclotetrasiloxane (D4).

Optimised latexes were blended

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 characterised using fourier transfer infrared spectroscopy, gel permeation chromatography and particle size analysis. The optimised 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 colour measuremets as well as stress strain analysis.

Clear films with low dirt pickup properties

The characterisation results revealed latexes with optimised conversion and uni-modal particle size distribution (PSD) were synthesised (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 optimised 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 optimised ratios leads to a good performance exterior and uniform hydrophobic coating.

The study is published in: Progress in Organic Coatings, Volume 102, Part B, January 2017, Pages 151–166