Effects of Interfacial Interaction on Corrosion Resistance of Polybenzoxazine/SiO2 Nanocomposite Coatings

The interfacial interaction between the two phases in polybenzoxazine/SiO2 nanocomposite coatings was controlled through modifying surface functionalities of SiO2 nanoparticles (SNP). SNPs with methyl, epoxide, and benzoxazine groups on the surface were prepared in this work, which was characterized by FTIR, TGA, and elemental analysis. The strong chemical bonding between nanoparticles and polybenzoxazine was obtained because of the reaction between epoxide groups or benzoxazine groups and benzoxazine molecular during the curing process. Both surface properties and corrosion resistance of composite coatings were fully investigated with the assistance of SEM, EDS, water contact angle measurement, and EIS technique. SNP incorporation could reduce porosity of the coatings so significant that all SNP loading nanocomposite coatings exhibited excellent corrosion resistance with a charge transfer resistance of over 1 G Omega cm(2) during 31 days' immersion in a 3.5 wt % NaCl aqueous solution, which was 3 orders of magnitude higher than the SNP-free polybenzoxazine coating after 31 days' immersion. It is evident that the proper interfacial strengthens by chemical bonding improved the stability of coatings' corrosion resistance considerably. The coating with epoxide groups modified SNP showed no penetration by corrosive medium during 31 days' immersion because of the strong chemical bonding between epoxide groups on SNPs and phenolic hydroxyl groups of polybenzoxazines without changing the original cross-linking structure of polybenzoxazine. Interfacial interaction between phases also plays a key role in the affinity between SNPs and polybenzoxazine, which determines the dispersion of SNPs in coatings and uniform morphology of composite coatings.