KH560–formic acid synergistically modified steel slag as a filler for alkyd resin composite coatings: Mechanical and anticorrosive properties

To address the issues of steel slag (SS) having high polarity, a tendency to agglomerate, and poor compatibility with alkyd resins, this study synergistically modified SS with formic acid and KH560 to obtain formic acid-KH560 synergistically modified steel slag (SMSS). SMSS was then compounded with petroleum resin to prepare a series of alkyd resin coatings (APC), which enhanced the mechanical properties and corrosion resistance of pure alkyd resin coatings.Formic acid reacts with and consumes Ca(OH)₂ and CaCO₃ on the SS surface, increasing the surface roughness of SS and providing active sites for KH560 modification. KH560 undergoes a condensation reaction with hydroxyl (-OH) groups on the SS surface, reducing the number of surface -OH groups, lowering SS polarity, and improving its dispersibility. Results indicate that the coating achieves the optimal comprehensive performance when the petroleum resin content is 2 wt.% and SMSS is used as the main filler. Specifically, its hardness, adhesion, flexibility, and impact resistance reach 2H, Grade 1, 10 cm, and 34.3 mm, respectively. After 336 h of salt spray testing, only slight rusting is observed, with a contact angle of 100.7°. The coating exhibits a corrosion current density of 2.7×10⁻⁷ A·cm⁻², a protection efficiency of up to 99.6%, and an impedance modulus of 4.3×10⁷ Ω·cm² at low frequencies. This study provides a theoretical basis and technical support for the high-value utilization of SS, and is expected to promote the resource utilization of industrial solid wastes.