Corrosion resistance of alkoxysilane modified bisphenol A-epoxide coatings

Abstract

Bisphenol A (BPA) epoxy was modified with amine functionalized silane (ASE) and isocyanate functionalized silane (ISE), and the modified epoxides were blended with both tetraethyl orthosilicate oligomers (TEOS oligomers) and titanium dioxide (TiO2). These hybrid networks were characterized by solid state 29Si-NMR, contact angle, crosslink density, pull-off adhesions, and crosshatch adhesion. Corrosion resistance was examined with a salt spray test, a filiform test and electrochemical impedance spectroscopy (EIS). Modified epoxides with addition of TEOS oligomer and TiO2 fillers showed improvement in mechanical properties. The broader degree of cross-linkage was observed in ISE based coatings. In contrast, ASE based coatings had a more uniform crosslink distribution and higher crosslink density. The addition of TiO2 fillers increase the percolation root of ISE epoxide, but was eliminated after blending with TEOS oligomer. With TEOS oligomer addition, crosslinked ISE showed complete condensation and high pull-off adhesion (153 lb/in2). The more homogeneous and higher crosslinked polymer matrix of ASE resulted in a higher diffusion resistance, and as a consequence exhibits good barrier protection under long term immersion conditions compared with the lower cross-linked ISE epoxide.