Electroactive additives into polyurethanes for high corrosion resistance coatings for mild steel

Abstract

There is a demand for innovative coatings such as polyurethane (PU) in industrial and commercial sectors to effectively combat corrosion on mild steel substrates. In this work, novel redox‐active polyurea (PUr) additives such as PUr‐diamine capped trimer (DCTA) and PUr‐diamine‐capped tetraaniline (DCTAni), derived from DCTA and DCTAni, were synthesized to enhance the anticorrosion properties of PU coatings. These are characterized using 1H nuclear magnetic resonance spectroscopy, Fourier transformed infrared, and high‐resolution mass spectrometry technical methods. These additives (2, 5, and 10 wt%) were dispersed in a polyurethane‐urea (PUU) matrix, which was synthesized from PTMG‐2000, and IPDI with dihydrazide adipate as a chain extender. The electroactivity of the coatings were evaluated using cyclic voltammetry (CV) and ultraviolet–visible spectroscopy. Furthermore, anticorrosion performance was assessed through electrochemical impedance spectroscopy and Tafel potentiodynamic polarization measurements. The optimal corrosion protection was achieved with increasing weight percent (wt%) of additive in PUU, showing a trend of 10% > 5% > 2%. Coatings reported maximum polarization resistance (Rp) of 122.15 MΩ, with corrosion rates (CR) as low as 2.38 × 10−6 mm/year. Accelerated salt spray testing over 600 h in a 5 wt% NaCl salt fog confirmed the coatings' durability. The microstructures of PUr particles were determined through FESEM characterization. Additive‐blended PUUs exhibited moderate tensile strength and elongation at break compared to the reference PUU matrix. The hydrophobicity of both the reference sample (PUU) and the additive‐blended coatings was measured, with the highest recorded value being at 93.1 ± 0.048 for 10 wt%. Thermal gravimetric analysis demonstrated polymer degradation with a maximum of T5% observed at 304.1°C.