Improving the corrosion resistance of waterborne epoxy resin coating by using silane modified Ca-Al LDH filler

In this study, 2-mercaptobenzothiazole (MBT)-intercalated Ca-Al layered double metal hydroxide (CaAl-MBT LDH) was prepared by a coprecipitation and ion-exchange method and then modified with the silane coupling agent KH550. The modified CaAl-MBT-KH550 LDH powder was characterised by X-ray diffraction, scanning electron microscopy, laser particle size distribution analysis, and sedimentation tests. The results show that the powder has a hexagonal morphology and a layered structure. The dispersion in waterborne epoxy resin was improved. Compared with the unmodified LDH, the modified CaAl-MBT-KH550 LDH had a larger particle size and a narrower particle size distribution. Electrochemical impedance spectroscopy test results showed that, within the scope of this experiment, the corrosion resistance of the epoxy resin coating was optimal when the amount of CaAl-MBT-KH550 LDH added was 2%. After soaking in a 3.5wt.% NaCl solution for 312h, the charge transfer resistance (Rct) of the coating with 2% CaAl-MBT-KH550 LDH was still as high as 8.96×108 Ω·cm2, while that of the coating with 2% unmodified CaAl-MBT LDH was only 2.76×106 Ω·cm2. The above results show that the silane-modified CaAl-MBT-KH550 LDH was helpful in improving the long-term corrosion resistance of waterborne coatings compared to before modification.