Water-based polyurethane formulations for robust superhydrophobic fabrics

Free radical copolymerization of acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), and monomethacryloxypropyl terminated poly(dimethyl siloxane) (PDMS-MA) yielded graft (g) copolymers P(AA-HEA)-g-PDMS. The molecular weights of the three used PDMS-MA macromers were 0.7, 5.0, and 10.0 kDa, respectively, and the respective weight fractions of AA, HEA, and PDMS-MA in the three synthesized copolymers were 10.0, 20.0, and 70.0 wt%. The copolymers were dispersed in water as micelles due to the water-soluble HEA units and salt formation from the AA groups with added triethylamine. Mixing these aqueous copolymer micellar solutions with a water-soluble blocked tetraisocyanate yielded water-based polyurethane (PU) formulations. Soaking fabric samples in such a water-based formulation and then withdrawing, drying, and heating the samples at 150 or 180 °C produced on the fabric fibers a crosslinked coating that was ∼220 nm thick and surface-enriched with PDMS. A systematic study was performed to investigate factors affecting the hydrophobicity of the coated fabric samples. These factors included varying the concentration of the aqueous P(AA-HEA)-g-PDMS coating solutions, the molar ratio of isocyanate groups to the AA and HEA groups, the coating curing times at 150 °C, and the molecular weight of the PDMS side chains. This study further established that the coatings could be cured in 7 min at 180 °C and fabric samples coated by P(AA-HEA)-g-PDMS_10k with PDMS molecular weight at 10.0 kDa were the most hydrophobic. The coatings were stable against real laundry tests, abrasion by sandpaper, and soaking in aqueous acid and base solutions. Thus, robust superhydrophobic fabrics were obtained from using a water-based environmentally friendly formulation and this coating process was convenient, rapid, and practical.