Enhancing corrosion resistance of epoxy resin coatings through dual modification of graphene oxide with maleic anhydride and paraphenylenediamine

Paraphenylenediamine (PPDA)-grafted maleic anhydride (MAH)-modified graphene oxide (PGO) was synthesized through a dual modification process. Initially, MAH was employed to modify graphene oxide (GO) to enhance its reactive sites. Subsequently, PPDA was utilized for further modification of MAH-modified GO (MGO). Through a comprehensive analysis, the successful grafting of MAH and PPDA onto GO was confirmed. It was concurrently established that the optimal ratio of PPDA to MGO is 1:1. This approach yielded PGO characterized by outstanding dispersibility and barrier properties in epoxy resin (EP) coaings for Q235 steel. The corrosion resistance of EP coatings containing varying amounts of PGO was assessed using electrochemical workstation and salt spray testing. After immersing in a 3.5 wt.% NaCl solution for 300 h, the composite coating containing 0.1 wt.% PGO exhibited superior performance in terms of low-frequency impedance modulus, measuring at 1.1 × 10⁸ Ω cm². The lowest corrosion current density was 2.32 × 10^–10 A cm⁻², and the self-corrosion voltage was −0.301 V. Additionally, polarization testing indicated that this coating also displayed the lowest corrosion rate, specifically 1.383 × 10^–7 mm/a.