Highly Anti-Corrosive Performance of Poly(Vinylidene Fluoride-Hexafluoropropylene)/Boron Nitride Nanosheet/Polyimide Composite Coating

Polyimide (PI) is one of the most important engineering plastics, but its stability in aqueous environments is insufficient, which limits its anti-corrosion efficiency. In this study, a novel P(VDF-HFP)/SMT-RS@BNNSs/PI composite coating is prepared by incorporating poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) and the exfoliated boron nitride nanosheets (BNNSs) which were highly co-functionalized with two kinds of materials of the rosin and the soy-maleic anhydride-tannic acid adhesive molecules (SMT-RS@BNNSs). The coatings are characterized in detail by using the XRD, FT-IR, XPS, and SEM technologies. Electrochemical impedance spectroscopy (EIS) and polarization curve tests further evaluated the corrosion resistance of the coating. As results, the obtained P(VDF-HFP)/SMT-RS@BNNSs/PI coating with good adhesion (grade 1) to the low-carbon steel plate displays a larger water contact angle of 93.10° compared to blank PI (75.5°) and SMT-RS@BNNSs/PI (83.2°). The dispersed distribution and interaction of SMT-RS@BNNSs can effectively reduce the phase separation between P(VDF-HFP) and PI. Even after soaking in electrolyte for 15 days, the impedance modulus, corrosion current, and corrosion voltage of the P(VDF-HFP)/SMT-RS@BNNSs/PI coating are 1.568 × 10¹⁰ Ω cm², 4.612 × 10⁻¹² A cm⁻², and 0.325 V, respectively. These properties are superior to those of the PI and SMT-RS@BNNSs/PI coatings. It is believed that the excellent anti-corrosive performance of this PI-based composite will broaden the application fields of PI materials.