Modified waterborne polyurethane with superior corrosion resistance
In the study, a double bond-terminated waterborne polyurethane prepolymer was firstly synthesized from polycaprolactone polyol, toluene diisocyanate, dimethylolpropionic acid and hydroxyethyl methacrylate. Then, waterborne polyurethane prepolymer was modified with styrene, butyl acrylate, glycidyl methacrylate, and dodecafluoroheptyl methacrylate though soap-free emulsion polymerisation method in order to obtain the crosslinked fluorinated acrylate modified waterborne polyurethane (CFWPUA).
Reduced water absorption rate
The CFWPUA emulsion was used as the matrix resin to prepare the coating with a bar coater, which possesses the characteristics of external hydrophobic surface constructed by long fluorinated side-chains and internal double cross-linking system. The results of infrared spectrum analysis proved the successful synthesis of modified waterborne polyurethane. The energy-dispersive X-ray spectroscopy results showed that the long fluorine side-chains partially migrate to the surface of the coating during the curing process, which leads to the occurrence of fluorine enrichment on the surface.
When the glycidyl methacrylate content is 5 wt% and the dodecafluoroheptyl methacrylate content is 7.5 wt%, the water absorption rate of the membrane reduces to 7.9%, the water contact angle of the coating reaches 102.5°, and the gel content is 91%, which proved the successful construction of the double cross-linking system and prevents the penetration of water molecules.
The pencil hardness of CFWPUA coating can reach 3H and flexibility and adhesion properties are at the highest level. Most importantly, in the electrochemical impedance spectroscopy test, the modified waterborne polyurethane coating effectively protects Q235 metal substrate from corrosion in a 3.5 wt% NaCl solution.
The study has been published in Progress in Organic Coatings, Volume 158, September 2021.