Enhanced adhesive and anti-corrosive performances of polymer composite coating for rusted metallic substrates by capillary filling

At present, mechanical de-rust technologies (grinding and sandblasting) are forbidden in some specific engineering fields such as oil drilling platforms equipped with storage tanks, chemical pipelines and power transmission system. It is passivated rust with cracks and holes that is known to hinder adhesion between anticorrosive coating and metallic substrate. This paper reported an organic-organic fluoropolymer/polyurethane (PF/PU) polymer coating, showing strong adhesion strength of 18.2 MPa with rust and 16.5 MPa after 240 h salt spray test, which is 2-3 times higher than conventional inorganic-organic epoxy (EP) coating (6-9 MPa). The PF/PU coating have protected rusted chemical pipelines from marine atmosphere corrosion for 3 years. Due to the micro/nano-channels in the rust layer, PF/PU precursor of appropriate surface tension and viscosity spontaneously adsorb/adhesive, wet, spread and fill with the channel by capillary force. A composite polymer-rust-iron substrate with three-dimensional interpenetrating network is fabricated via mechanical interlocking/chemical bonding and PU cross-linking. The physical model of "capillary filling of polymer coating in micro/nano-rust-channels (mu/nRCs)" is proposed and demonstrated by "spinning by air cushion escaping" phenomenon as one end of the channel sealed. Based on researches and practical engineering applications on chemical pipelines and subway/railway tracks, a new polymer coating technology with rust towards on-site maintenance has been developed, aiming to realize the surface function remanufacturing of high-tech equipment served in severe corrosive medium and improve reliability of the equipment.