Interfacially adhesive corrosion protective fluoropolymer coatings modified by soybean extract

[Display omitted] •Soybean extract additive enhances both PVDF-HFP’s adhesion and corrosion protection.•Extract was obtained via a low-cost, facile, and eco-friendly method.•Increasing extract concentration leads to stronger coating adhesion.•Coating with 0.5 wt% extract displayed the highest corrosion resistance in NaCl solution.•Adhesion improvement results are supported by finite element analysis. Fluoropolymers are gaining interest from the coating industry thanks to their mechanical integrity, thermal stability, hydrophobicity, and chemical inertness. However, their nonstick nature limits their applications as it often leads to poor film adhesion to various surfaces. While various approaches have been explored to improve fluoropolymer adhesion, their practical application remains restricted due to their complexity, cost, and environmental impact. In recent years, extracts from fruits, leaves, and plants have been used as eco-friendly additives for polymer coatings due to their ready availability, sustainability, low toxicity, and compatibility. Herein, soybean extracts (SEs) were employed as a green additive to enhance both the surface adhesion and corrosion protection of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) coatings on carbon steel. Results showed that the inclusion of SEs increased the affinity between the fluoropolymer coating and metal surface. This improvement is attributable to the presence of abundant heteroatoms and pi-electrons from isoflavones in SEs and their capability to facilitate interactions at the coating-metal interface. Moreover, the coatings were able to suppress corrosion in 3.5 wt% NaCl solution, peaking an impedance modulus of ∼108 Ω cm2 after 7 d of continuous immersion, even at low SE doses. This result was supported by microscopic, spectroscopic, wettability, surface mechanical, thermal stability, cyclic corrosion, and simulation studies. Overall, our strategic approach highlights the beneficial use of SE additives toward formulating cost-effective, sustainable, and high-performance fluoropolymer coatings for a wide range of surface protection applications.