Non-fluorinated hydrophobic PDMS-PU copolymer formulations as an alternative to conventional water-repellent coatings

M. Rutkevičius, M. Geiger, S. Khan
NCSU,
United States

Keywords: hydrophobic, coatings, PDMS, textile

Summary:

Industries face tougher regulations on the C-8 fluorocarbon use in their waterproof coatings. The performance of these alternative coatings in terms of their life time and water repellency is not satisfactory. To overcome these issues, we designed a polymer, benefitting from the high strength of urethanes and the hydrophobicity of PDMS. We have linked individual monomers into a copolymer using isocyanate chemistry and dispersed the polymer in water. Our polymerization reaction design approach is particularly attractive to industries, because it allows easy scale up. We used dip coating and layer-by-layer deposition approaches to coat cotton fabrics with the PDMS-PU polymer dispersion. We demonstrate how the coating performance on cotton substrates depends on: i) different molecular weight of the initial building blocks, ii) polymer dispersion average particle size, and iii) added silica particles. Smaller molecular weight of the hydrophilic polyurethane increased water contact angle by ca. 20 °. Increasing molecular weight of PDMS increased contact angle by ca. 10 °. Controlling water addition rate allowed to obtain different particle sizes, ranging from 70 nm to ~3 µm. Scanning Electron Microscopy showed individual polymer particles fusing together upon curing of the coating and the particles showed inherent hierarchical roughness. Addition of as low as 0.1 wt% of hydrophobized silica particles into the formulation increased water contact angle by 10 ° and further increase was observed with additional silica content. In future, we plan to increase the hydrophobicity by using advanced coating application techniques and incorporation of hydrophobic functional particles, which will further the nano-roughness and hydrophobicity of the final coating.