Chitosan-based coatings to prevent Nitratidesulfovibrio vulgaris influenced (bio)corrosion on aluminium alloy

Chitosan, a natural polymer derived from chitin, is widely recognized for its biocompatibility, biodegradability, and in particular antimicrobial properties. This study investigates the effectiveness of chitosan grafted onto aluminium Al 2024 alloy substrates in preventing (bio)corrosion, specifically in the presence of the sulfate-reducing bacterium Nitratidesulfovibrio vulgaris (formerly Desulfovibrio vulgaris), a model organism for biocorrosion. Chitosan-based coatings of micrometer thickness were applied using a dip-coating method, which is easy to implement in industrial settings. The coatings were applied to both mirror-polished aluminum substrates, with and without triethoxysilylpropylsuccinic anhydride (TESPSA) for functionalization. Weight loss analysis, profilometry, epifluorescence microscopy, and X-ray photoelectron spectroscopy (XPS) were conducted on the chitosan-coated aluminium alloy before and after microbial incubation. The results showed that chitosan coatings, particularly those functionalized with TESPSA, significantly reduce (bio)corrosion and microbial growth. Notably, the 2 % w/v chitosan coating demonstrated strong adhesion, with less than 5 % detachment under tape tests and no detachment observed after five weeks of exposure to N. vulgaris, and substantial (bio)corrosion resistance. Epifluorescence microscopy revealed a nearly tenfold decrease in bacterial coverage compared to the uncoated substrate. XPS showed minimal impact from N. vulgaris on the 2 % w/v chitosan-coated aluminium, with a stable C/N ratio of 7.4 + /- 0.2 before and after incubation. Electrochemical corrosion tests indicated that the combination of chitosan coatings and TESPSA functionalization significantly decreases the corrosion rate, despite a minor increase in susceptibility to corrosion. These findings highlight the potential of chitosan-based coatings, especially when paired with surface treatments like TESPSA functionalization, to effectively combat corrosion and (bio)corrosion of aluminum alloys.