Cellulosic Hydrogels Comprising Cellulose Nanocrystals or Chitin Nanocrystals for Historic Ceramic Conservation

Over time, antique ceramics undergo a series of chemical and physical degradation processes, such as salt crystallization or the accumulation of atmospheric pollutants, which compromise their structural and aesthetic integrity. To restore and conserve cultural heritage artifacts, polymeric gels have been developed, where, in comparison to conventional petroleum-derived materials, naturally occurring polymers offer enhanced properties in terms of tunable viscoelasticity, high water retention capacities, low toxicity, and inherent biodegradability. Accordingly, here, we develop nanocomposite gels based on hydroxypropyl cellulose and incorporated biocolloids with anionic and cationic surface charges, cellulose nanocrystals (CNCs), or chitin nanocrystals (ChNCs). To enhance the durability and ductility of the hydrogels, chemical cross-linking with citric acid and plasticization with ethylene glycol are performed. Tunable Young's modulus (17.2-145.4 MPa) and elongation at break (14.3-109.1%) are obtained. Cleaning studies are carried out on actual 17th-19th century ancient ceramics from an archeological site in Bizkaia (Basque Country, Northern Spain). The hydrogels are applied directly onto the ceramics to set a continuous solid-liquid interface with no need for external mechanical pressure. X-ray fluorescence results reveal the hydrogels removing up to 72% of the lead in ceramics in 8 h of treatment, making those materials particularly suitable to remove traces of hazardous substances that are integral materials in various traditional crafts and cultural heritage artifacts. The strategy of incorporating biobased colloids within a cellulosic hydrogel allows for tuning its chemical and physical properties and introduces additional hydroxyl and amine/acetamide moieties that act as Lewis bases to enable chelation and electrostatic attraction effects for the cleaning process.