Polybenzoxazine/Epoxy Composite Coatings: Effect of Crosslinking on Corrosion Resistance
2021
Zhou, Changlu | Fu, Ming | Xie, Hanyu | Gong, Yanwei | Chen, Jiawen | Liu, Juan | Xin, Zhong
The crosslinking structure of polybenzoxazine/epoxy (PBE) composite coatings was controlled by a polymerization reaction between a benzoxazine (Bz) precursor bearing 1–3 Bz rings and epoxy. The structure was confirmed by Fourier-transform infrared spectroscopy (FTIR). Electrochemical impedance spectroscopy was used to monitor the corrosion resistance of the PBE coating. A good barrier coating with a high crosslinking density was obtained by incorporating a Bz precursor with 2 or 3 Bz rings, which showed a much higher gel content of ∼99% than the system (gel content: ∼66%) derived from a Bz precursor with only one Bz ring. Additionally, an increased charge-transfer resistance of approximately 1–3 orders of magnitude greater than that of the other system was observed during the immersion process. The influence of hydrogen bonding was also investigated in this paper by curve-fitting of the corresponding FTIR spectra, which is another important factor that determines the coating’s resistance to corrosion. As a result, the coating with high crosslinking density and less intermolecular hydrogen bonding content exhibited the best performance with a high charge-transfer resistance of over 1 GΩ cm² and a low double-layer capacitance of ∼7 nF cm–² during 80 days’ immersion in a 3.5 wt % NaCl aqueous solution.
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