Improving water resistance of epoxy based coatings by chemical modification with γ-isocyanatopropyltriethoxysilane

Five percentage mass ratio to epoxy of gamma-Isocyanatopropyltriethoxysilane (ICPTES) is grafted successfully onto fundamental chain of epoxy resin to improve the resistance against water of epoxy/polyamide (EP/PA) coatings on Al alloy surface. To further improve water resistance after cured ICPTES grafting EP/PA, different amounts ICPTES are incorporated. The capacitances of ICPTES grafting and unmodified EP/PA coatings after dipping in NaCl solution for different intervals, which are measured by electrochemical impedance spectroscopy, are employed to calculate the two kinds of volume percentage of water uptake dipping in solution for different intervals. The absorption behaviour of water in two kinds of coatings are analysed. The capacitances of later added ICPTES coatings are also measured by electrochemical impedance spectroscopy. The results show that water absorptivity of the modified resin coatings first decreases with the increase in total ICPTES content and then increases when total ICPTES content is more than 7% mass, and the diffusion behaviour of water in modified resin coatings does not obey the Fick's second law.