Nuovi idrogel eco-sostenibili di origine sintetica e naturale per diverse applicazioni

Hydrogels have garnered significant attention in different fields. However, traditional hydrogel synthesis often involves non-renewable resources and harsh chemicals, raising environmental concerns. Developing eco-sustainable hydrogels using natural polymers and green synthesis methods is essential for reducing environmental impact and enhancing sustainability. This doctoral thesis focuses on synthesizing eco-sustainable hydrogels, particularly organic-inorganic hybrid hydrogels and bacterial cellulose (BC) hydrogels. Polyvinyl alcohol (PVA) and tetraethyl orthosilicate (TEOS) were chosen for their properties aligning with green chemistry. PVA's hydro-solubility and biocompatibility, combined with TEOS's ability to interact with PVA in the sol-gel process, resulted in Class II hybrids with covalent interactions between inorganic and organic phases, as confirmed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). However, challenges such as fragility and long-term stiffness arose due to TEOS hydrolysis and condensation, indicating the need for optimized synthesis conditions. The core research involved BC hydrogels derived from kombucha. Kombucha biomass was used as a starter for hydrogel biosynthesis in sweetened tea and two low-cost media from industrial wastes: milk whey (MW) and brewery spent grains (BSG). The substrate composition influenced cellulose yield, with BSG providing results comparable to sugared substrates. Various analytical techniques, including Field Emission Scanning Electron Microscopy (FE-SEM), ATR-FTIR, X-ray Diffraction (XRD), and Simultaneous Thermal Analysis (TG-DSC), characterized the samples. A purification protocol involving sodium hydroxide treatment yielded pure cellulose hydrogels, displaying high crystallinity, significant water holding capacity (WHC), and consistent chemical structure across different substrates. However, microstructural characteristics, surface area, and WHC varied due to substrate composition. To enhance BC yield from low-cost sources, innovative approaches were explored. Enzymatic hydrolysate of BSG significantly increased yield to 5.4 g/L, while multi-microorganism fermentation of MW did not show substantial increases. Additionally, four Kombucha cellulosic by-products from brewing industries were characterized. These by-products exhibited uniform chemical structure and crystallinity but varied in microstructure and WHC due to different production processes. Some by-products were tested in new applications. BC hydrogels were investigated for use in the conservation and restoration of cultural heritage as solvent carriers. While synthetic hydrogels are commonly used in this field, their high costs and lack of renewability and biodegradability necessitate sustainable alternatives. A BC organogel loaded with ethyl acetate effectively removed beeswax from marble, as confirmed by μ-Raman spectroscopy and ATR-FTIR analysis. Another BC hydrogel loaded with ethylenediaminetetraacetic acid (EDTA) successfully removed copper corrosion stains from marble. Additionally, a novel antimicrobial hydrogel was formulated by functionalizing BC hydrogel with ozone, aimed at stone biodeterioration. Ozonated BC hydrogels, characterized by ATR-FTIR and rotational rheometry, completely suppressed selected biodeteriogenic microorganisms. On contaminated marble, brick, and biocalcarenitic stone, the highest concentration of ozone demonstrated significant antimicrobial activity, highlighting its potential as a sustainable, cost-effective treatment. This research lays the groundwork for future studies focused on refining synthesis techniques and exploring broader applications for eco-sustainable hydrogels.