| MA Ji-yuan,GUO Hui,ZHANG Xin-yue,LI Chuan-peng,XIE Jie,LUO Lai-zheng,ZHOU Kun,LIU Jie.Failure Behavior of Polyurethane Coating Immersed in Real Seawater[J],52(1):178-186 |
| Failure Behavior of Polyurethane Coating Immersed in Real Seawater |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.01.018 |
| KeyWord:polyurethane coating real seawater immersion test protective performance chemical structure failure behavior electrochemical impedance spectroscopy |
| Author | Institution |
| MA Ji-yuan |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
| GUO Hui |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
| ZHANG Xin-yue |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
| LI Chuan-peng |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
| XIE Jie |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
| LUO Lai-zheng |
Weathering Test and Research Center of Science Technology and Industry for National Defense, Southwest Technology and Engineering Research Institute, Chongqing , China |
| ZHOU Kun |
Weathering Test and Research Center of Science Technology and Industry for National Defense, Southwest Technology and Engineering Research Institute, Chongqing , China |
| LIU Jie |
School of Chemistry and Chemical Engineering, Yantai University, Shandong Yantai , China |
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| Abstract: |
| Polyurethane coating shows good characteristics of corrosion resistance and water repellency, and it is easy to repair. Thus, it is widely used in corrosion protection of marine engineering equipment. However, the protective performance of the polyurethane coating is often lost for effects of various factors such as dissolved oxygen content, temperature, and seawater scouring during its service in the marine environment. The work aims to conduct real seawater immersion test in Xiaomaidao Test Station of Qingdao to study the failure behavior of the polyurethane coating immersed in real seawater. In this work, the Q235 carbon steel (100 mm × 75 mm × 2 mm) was used as the metal substrate, and the TS55−80 polyurethane coating was sprayed on the surface of the metal substrate. The test samples of the TS55−80 polyurethane coating/Q235 carbon steel system was immersed in the seawater. The test samples were divided into 6 cycles:0 month, 1 month, 3 months, 6 months, 9 months, 12 months. The macro morphology and micro morphology of the polyurethane coating surface was observed with an electronic magnifying glass. The appearance changes of the polyurethane coating were evaluated by measuring and calculating the gloss loss and color difference of the coating. A pull−off adhesion tester was used for the adhesion testing following ASTM D4541−02, and the diameter of the dolly was 20 mm. The EIS measurements were conducted within the frequency range of 100 kHz-10 mHz at room temperature with an electrochemical test system, the amplitude was 20 mV and the test area was 1 cm2. The EIS spectra were analyzed with the ZSimpWin 3.30 software. The chemical structures of the coating samples were analyzed by FT−IR and XPS. The binding energies in the XPS test results were calibrated by reference to the C1s signal at 284.8 eV. Thermal stability of the polyurethane coating was evaluated with a thermal gravimetric analyzer under a nitrogen flow (10 cm3/min). It showed that when the polyurethane coating was immersed in seawater for 6 months, obvious bubbles and cracks appeared on the surface of the coating, and the corrosion products were observed. With the immersion time increased, the chemical structure of the coating was changed, and the thermal stability of the coating was significantly decreased. After immersed for 12 months, the gloss loss rate of the polyurethane coating was 69.9%, which was a serious gloss loss. The color difference of the coating was 3.20, which was a slight discoloration. The adhesion of the coating was decreased to 0.82 MPa, which indicated that the bonding strength between the coating and the metal substrate was significantly decreased. And the impedance value of the coating was decreased to 2.81×103 Ω.cm2, which meant that the protective performance of the polyurethane coating was basically lost. When the polyurethane coating is immersed in real seawater, the shedding of pigment particles would cause the number of pores on the coating surface to increase, the penetration of corrosive media in seawater would be accelerated. Thus, the electrochemical reaction at the coating/metal interface rapidly developed, resulting in the significant decrease of the protective performance of the coating. In addition, the hydrolysis of urethane bonds in the polyurethane chains is the main reason for degradation of the polyurethane coating. |
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