While a variety of synthetic and natural polymers are currently employed in restoration, many present significant drawbacks regarding long-term stability and material compatibility. Acrylics, epoxies, and aliphatic resins remain the primary polymers used in restoration. For instance, Aquazol (poly-2-ethyl-2-oxazoline) is frequently applied in water or alcohol solutions though it is often used, like Paraloid B72, as an adhesive rather than a paper binder, due to its glossy nature. Furthermore, in the restoration of ancient paintings, application of Aquazol and analogous consolidants may be disadvantageous, due to their hygroscopic nature. Epoxy resins, typically used in stone processing, are also widely used to treat macroscopically decoupled wooden artifacts, suffering from fractures, loss of woody components, biological decay. Aliphatic resins, a more recent development in the field, are utilized not only in paint formulations but also as gentle consolidants for degraded wood [1]. In the specific context of paper conservation, practitioners rely on cellulose derivatives, synthetic adhesives, natural products and nanomaterials. Klucel G (hydroxypropylcellulose), in ethanol or isopropanol, is an example of a cellulose-derived consolidant, among the most widely used due to its reversibility and flexibility. Natural consolidant, such as animal or vegetable gelatins, also play an important role in this field. This category includes Gellan gum, obtained from bacterial fermentation, often utilized for wet cleaning treatments [2]. Building upon this existing framework, the present study aims to address the environmental and functional limitations of these traditional materials. By leveraging crystalline and bacterial nanocellulose, this research aims to develop an innovative hydrogel which would serve as a consolidant for cellulosic materials such as textile fibers, paper, and wood, ensuring the treatment is both sustainable and compatible with the delicate substrates it protects and offers a greener and more effective alternative for the preservation of cultural heritage. The first part of the research work consisted in the extraction of crystalline cellulose from different sources, such as cotton wool or pineapple crown leaves. The first attempt was performed on cotton wool, basing on a literature protocol [3]. Cotton wool was pretreated by acid hydrolysis to increase alpha cellulose and facilitate fiber extraction. Subsequently, nanocellulose was extracted by disintegrating the previously treated cotton fiber with TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), NaBr and NaClO in a carbonate-bicarbonate solution at pH 10. After nanocellulose extraction, a nanocellulose film was produced. Suspensions of cellulose nanofibrils (CNF) at different concentrations were homogenized by stirring to obtain a uniform distribution of CNF. Furthermore, the same concentration of CNF was dried at different temperatures to evaluate the consistency of the film obtained with different drying speeds [3]. In the meanwhile, a different protocol was used to extract cellulose fibers from pineapple leaves, for a comparison with material obtained from cotton wool [4]. Cellulose fibers were extracted from pineapple leaves by maceration of leaves in water for about 20 days, followed by manual separation and drying of fibers, to reproduce the retting process usually applied to natural fibers as hemp [4]. A morphological study of the cellulose fibers and the CNF film was conducted using scanning electron microscopy (SEM) or transmission electron microscope (TEM), to determine the morphology of the nanocellulose. Additionally, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to determine the structure of the extracted cellulose fibers.

A first tentative preparation of hydrogel was finally performed starting from both the nanocellulose extracted from cotton and pineapple leaves, applying a pre-existing protocol [5].

Scanning electron microscopy was then used to characterize the hydrogels, to detect potential structural differences between the cellulose gels produced.

References

1- L. Borgioli, P. Cremonesi, Le resine sintetiche usate nel trattamento di opere policrome (Synthetic resins used in the treatment of polychrome works). Collana I Talenti, 2005, Padova, Italy, Il Prato.

2- C. Isca, L. Fuster-López, D. J. Yusa´-Marco, A. Casoli Cellulose, 2015, 22, 3047.

3- A.R. Lapuz, S. Tsuchikawa, T. Inagaki, T. Ma, V. Migo Crystals 2022, 12, 601.

4- V. Johny, A.K. Mani, S. Palanisamy, V. K. Rajan, M. Palaniappan, C. Santulli Fibers 2023, 11, 5.

5- L. Zhang, Y. Li, M. W. Ullah, Z. Wang ACS Sustain. Chem. Eng. 2026, 14, 3734.