Abstract
In this paper, an environmentally friendly waterborne polyurea (WPUA) emulsion and its corresponding coating were prepared, which was characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). To improve the performance of the coating, we doped sulfonated graphene (SG) into WPUA to prepare composite coating (SG/WPUA). SG can be uniformly dispersed in WPUA emulsion and is stable for a long time (28 days) without delamination. The water resistance of the composite coating with 0.3 wt.% SG nanofiller was improved; the water contact angle (WCA) result was SG/WPUA (89°) > WPUA (48.5°), and water absorption result was SG/WPUA (2.90%) < WPUA (9.98%). After water immersion treatment, SEM observation revealed that the SG/WPUA film only generated enlarged microcracks (100 nm) instead of holes (150–400 nm, WPUA film). Polarization curves and electrochemical impedance spectroscopy (EIS) tests show that SG nanosheets with low doping content (0.3 wt.%) are more conducive to the corrosion resistance of WPUA coatings, and the model was established to explain the mechanism.
Highlights
Polyurea coatings, especially mainstream commercial 2K-polyureas, have been challengingly applied to high-speed railways, bridges, vehicles, oil and gas pipeline engineering, bulletproof and explosive loads, etc. [1,2,3,4]
The infrared spectrum of Graphene oxide (GO) confirmed the existence of C–O, C–O–C, and C–OH
The strong peak in the range of 3434–3330 cm−1 is the vibrational absorption peak of –OH, which is attributed to the oxidation of GO
Summary
Especially mainstream commercial 2K-polyureas, have been challengingly applied to high-speed railways, bridges, vehicles, oil and gas pipeline engineering, bulletproof and explosive loads, etc. [1,2,3,4]. The self-emulsified polyurea is electrostatically stabilized in water by introducing hydrophilic structural units into the macromolecular chain, but the corresponding coating may have poor water resistance due to its high dispersion in water. Shrinkages, breaks, and internal defects in the coatings caused by water volatilization are inevitable during the coating forming process [12] These inherent problems will seriously weaken the coatings’ resistance to the corrosive medium, resulting in a greatly shortening coating life. The reduction reaction of the oxygen-containing groups eliminates the surface defects of graphene to a certain extent. In this strategy, SG can be uniformly and stably dispersed in the WPUA emulsion, resulting in a barrier network that can effectively improve the corrosion resistance of the coating. The water-resistance and corrosion-resistance of composite coatings were systematically evaluated, the optimal mixing ratio of SG was explored, and the corrosion resistance mechanism of the composite coating was studied by establishing a model
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