# Recent Developments in Materials Science for the Conservation and Restoration of Historic Artifacts
## 5 Biopolymers: Sustainable Conservation Solutions
### Case Studies
[95] presented the use of chitosan-based coatings with embedded corrosion inhibitors, specifically benzotriazole (BTA) and mercaptobenzothiazazole (MBT), to protect copper-based alloys, such as bronze, commonly found in cultural heritage artifacts. According to the presented results, both BTA and MBT, when incorporated into chitosan coatings, showed improved corrosion inhibition for bronze alloys. BTA, in particular, provided superior protection. The study highlighted a synergistic effect where the chemical properties of these inhibitors combined with the physical barrier of the chitosan polymer matrix enhanced corrosion resistance more effectively than chitosan alone. The chitosan coatings were optimized to meet the aesthetic requirements essential in cultural heritage conservation, such as maintaining the appearance and texture of bronze artifacts. The coatings were found to be minimally invasive and could be applied and removed without causing damage, making them suitable for use on valuable, irreplaceable artifacts. In contrast to traditional synthetic coatings, this chitosan-based system uses non-toxic solvents that can be easily removed. The study revealed that glucono delta-lactone (GDL) is more effective than acetic acid (AcOH) in preparing the chitosan films, as it avoids forming lead-based platelets that could affect the coating's quality. Accelerated corrosion tests and an image analysis confirmed the effectiveness of BTA and MBT chitosan coatings in preventing corrosion. Post-treatment analyses using microscopy and spectroscopy showed that the coatings maintained a high level of surface integrity, demonstrating potential for long-term protection of indoor bronze artifacts [95]. [PERSON] et al. [96] evaluated the short-term effects of two biopolymers--a bacterial biopolymer and a plant-based biopolymer, Escobila (_Sida rhombifolia_)--as potential protective coatings for limestone surfaces in tropical conditions. The research, conducted over a 30-day period on both sound and deteriorated limestone, measured surface hardness and color changes to evaluate the efficacy of these biopolymers in enhancing limestone durability without compromising its appearance. According to the results obtained, both the bacterial and plant-derived biopolymers demonstrated an ability to increase the surface hardness of limestone blocks, an effect particularly notable when using the Escobila polymer, which has a complex carbohydrate structure, contributing to a more stable surface that resists physical degradation under tropical environmental conditions. Unlike many traditional stone coatings, neither biopolymer significantly altered the color of the limestone surfaces, maintaining the aesthetic integrity of the material. This result is especially important for heritage conservation, where preserving the original appearance is essential. The study's biochemical analysis revealed that Escobila is rich in heteropolsaccharides with some anionic components, which are likely responsible for its consolidating effect. These compounds appear to contribute to surface stabilization by enhancing cohesion within the limestone's structure. Drawing on historical Mayan construction practices, which incorporated organic additives in lime mortars, the study reinforced the potential for biopolymer additives to protect and restore historical stone materials. However, it emphasized that a longer assessment period and compatibility testing with traditional building materials are necessary for practical conservation applications. [PERSON] et al. [97] evaluated the protective potential of three biopolymers--polylactic acid (PLA), chitosan, and polyhydroxyalkanoate (PHA)--in preventing air pollutant-induced degradation, specifically black crust formation, on marble artifacts. The marble head from the Greco-Roman period, currently housed at the Grand Egyptian Museum, served as the focal artifact, while experimental marble samples were used to assess each biopolymer's efficacy under controlled conditions.