The influence of organophosphonic acid and conducting polymer on the adhesion and protection of epoxy coating on aluminium alloy

• A new bilayer system has been developed for the protection of aluminium surface.
• Non-blistering formation were observed thanks to the good adherence between silane–aluminium and silane–epoxy interfaces.
• Synergistic combination of silane and organophosphonic acid for effective covalent bonding to metal substrate.

In the present study we compared the beneficial effect on the incorporation of modified silane nanocoating and conducting polymer additive to the adhesion and protection of aluminium surface with epoxy coating. Results proved that the protection imparted by the silane coating, suitably modified with phosphonic groups, showed an excellent adhesion to the metallic substrate as well as good adherence with the epoxy outer layer, which result in an improved corrosion resistance. The incorporation of 1% of poly(3-methyl thiophene acetate) (P3TMA) also improved the adhesion force of the epoxy paint adhered to the aluminium surface. However, the adhesion force decreased with the increase of the immersion time in NaCl 3.5% solution. In conclusion, both bilayer systems [vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) and VTMS/TEOS/ethylenediaminetetra(methylene phosphonic acid) (EDTPO)] and also the employment of P3TMA in the epoxy coating showed better results in accelerated corrosion assays, i.e. very low blistering formation was observed, compared with control samples based in a monolayer coating directly adhered to the aluminium surface.

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