Sustainable biopolymers as protective coatings against indoor corrosion of bronze: A comparison among alginate, carboxymethyl cellulose, chitosan and pectin

This study investigates the anticorrosion properties of four polysaccharide-based biopolymers, i.e., alginate, carboxymethyl cellulose, chitosan, and pectin, to develop sustainable protective coatings against indoor degradation of bronze. The ability of biopolymers to limit the diffusion of moisture and airborne degrading species, such as Cl− ions, was thoroughly evaluated, as these factors seriously affect the stability of bronze artifacts in museum environments. The final goal was to obtain transparent, colourless, and homogeneous coatings that preserve the original appearance of the metal surface, while ensuring durable protective performance. The anti-corrosion efficacy of the coatings was carefully evaluated by performing different ageing treatments and comparing the results with a commercial acrylic resin (Paraloid B72), selected as a benchmark.Our findings showed that biopolymer coatings, although hydrophilic, impart effective protection to bronze surfaces, hindering the diffusion of airborne degrading species. Particularly, the coating based on carboxymethyl cellulose exhibited the best protective efficacy compared with the other biopolymers, both during accelerated corrosion treatments and long-term natural ageing. The study also showed that biopolymer coatings exposed to real museum environments prevent the accumulation of dust and soiling particles better than the commercial acrylic resin.Overall, these results highlight the potential of biopolymers as innovative and eco-friendly materials for the long-term preservation of bronze artifacts in indoor environments.