Synthesis of acrylated tannic acid as bio-based adhesion promoter in UV-curable coating with improved corrosion resistance

Aiming to developing UV-curable coatings with high performance on metal surface, acrylated tannic acid (TA-GMA) was developed to be a new bio-based adhesion promoter, which was synthesized via the ring opening reaction of tannic acid (TA) and glycidyl methacylate (GMA). The acrylation of TA not only improve the compatibility of TA with UV-curable resin, but also participate in the photo-curing process, which could act as a "bridge" between the coating and the metal substrate. The structure of TA-GMA was determined by FT-IR and 1H NMR. The adhesion promotion effects of TA-GMA for UV-curable coatings on metal substrates were investigated with cross-hatch test and pull off analysis. The results showed that TA-GMA could significantly improve the adhesion strength between UV-cured coatings and metal substrates. The pull-off strength increased from 0.44 MPa to 1.65 MPa for low carbon steel plate and from 0.13 MPa to 1.11 MPa for aluminum plate with the presence of TA-GMA, respectively. A significant increase in cross-hatch adhesion level was also observed. Accompanied with the remarkably improved adhesion performance, the corrosion protection properties of the UV-cured coating with TA-GMA were significantly enhanced from both electrochemical impedance spectroscopy (EIS) test and salt spray results.