Investigation of chemical, physical and mechanical properties of hybrid chitosan-silica based coatings for aluminium substrate

This paper describes the development and characterization of eco-friendly hybrid coatings using chitosan and tetraethoxysilane (TEOS) through sol-gel processing onto aluminium substrates. Firstly, we investigated the impact of curing temperatures and the addition of a coupling agent (VTMS) on various physical and chemical properties to determine the optimal composition, to achieve crack-free and uniform films. Chemical and physical properties were assessed via FTIR spectroscopy and SEM imaging, while surface wettability was analyzed through water contact angle measurements, and hydrolitic degradation tests were also performed. Since the mechanical strength of bonding is important for protective coatings, the mechanical characterization of optimized films was conducted by pin-on-disk and scratch tests to understand their elasticplastic and adhesive behaviour. Finally, the antibacterial properties were also studied and discussed. The results indicate that an annealing temperature of 100 degrees C and the incorporation of vinyltrimethoxysilane (VTMS) as a coupling agent are essential for producing homogeneous, stable coatings with excellent hydrolytic degradation resistance. The addition of VTMS effectively addresses common challenges associated with hybrid sol-gel coatings, including cracking, porosity, and poor substrate adhesion. Subsequent investigations revealed that both the presence and concentration of chitosan within the hybrid sol-gel coatings significantly enhance mechanical resistance, water resistance, and friction reduction. A strong correlation between increased coating hydrophobicity and decreased coefficient of friction confirms the intrinsic lubricity of chitosan-silica sol-gel coatings. These coatings also exhibit antibacterial properties compared to both the uncoated aluminium substrate and pure silane coatings. Overall, these findings underscore the multifunctional benefits of chitosan-containing hybrid coatings, positioning them as a promising sustainable, transparent, self-lubricating, and water-resistant coating solution for anodized aluminium substrates.