The conservation of historical aluminium aircraft exposed to outdoor conditions requires protective systems combining corrosion mitigation, aesthetic compatibility and chemical stability. Within the PROCRAFT project two advanced coatings, namely, a bio-based cutin-derived polyurethane and a 3-mercaptopropyl trimethoxysilane (PropS-SH)-based system, were comparatively evaluated against the benchmark Paraloid B72 (PB72) on historic corroded and painted Duralumin substrates dating from World War II and the immediate post-war period. Coupons were subjected to an accelerated ageing protocol including simulated acid rain runoff, followed by thermo-hygrometric and UV cycling. Protective performance was assessed through a multi-analytical approach integrating electrochemical tests, colour analysis, SEM-EDS, ATR-FTIR, μ-Raman, and metal release quantification by MP-AES. On corroded substrates, both innovative coatings exhibited higher polarization resistance than PB72 and values two orders of magnitude greater than those of uncoated surfaces after ageing. PropS-SH provided inhibition efficiencies ≥95% in terms of Al release, while the cutin-based coating achieved inhibition efficiencies >85%, outperforming PB72 under the same conditions. On painted substrates (already intrinsically protective) PropS-SH produced up to a one-order-of-magnitude increase in polarization resistance compared to the original paint system, whereas PB72 provided only marginal improvements. Spectroscopic analysis after ageing revealed progressive siloxane network densification in PropS-SH and, in the cutin-based coating, continued crosslinking accompanied by UV-mitigating behaviour attributable to residual natural antioxidants. Overall, both coatings provided effective corrosion protection on painted and corroded substrates, with PropS-SH exhibiting superior performance in suppressing metal release and enhancing polarization resistance, while maintaining good aesthetic stability throughout the artificial ageing process. • New strategies for preventing corrosion of historic Al-alloys wrecks. • Outdoor exposure simulated through accelerated ageing. • Assessment of cutin-based polyurethane and 3-mercaptopropyl trimethoxysilane coatings. • Evaluation of colour, physical and chemical changes after ageing. • Best metal release suppression and highest polarization resistance for PropS-SH.
Lozano et al. (Sun,) studied this question.