# Comparative Studies on Nanocellulose as a Bio-Based Consolidating Agent for Ancient Wood
## 2 Materials and Methods  
### Materials  
All reagents and solvents were of analytical grade and were purchased from Merck. A Milli-Q Element System (Millipore, Molsheim, France) was used to obtain high-purity water for sample preparation and all dilutions. The CNC was prepared following a procedure reported in the literature, with partial modification [25]. Briefly, cotton pulp was hydrolyzed with sulfuric acid (64% \(w/v\)) to separate the nanocrystalline phase. An acid/cellulose ratio of 8.75 (\(w/w\)) was chosen. The reaction was carried out for 30 min at 60 \({}^{\circ}\)C, and then, the hydrolysis was quenched with iced water. The obtained suspension was centrifuged at 6000 rpm for 10 min to eliminate excess water and acid. The precipitate was suspended in distilled water and centrifuged until an opalescent suspension was obtained. The purification of the CNC suspension was carried out using dialysis membrane tubes (cut-off 10-12 kDa, Sigma-Aldrich, St. Louis, MO, USA) in ultrapure water, changing the water every 24 h. The final suspension pH was adjusted to 7 by a small amount of NaOH solution.  
Wood samples were obtained from a beam from the 16 th century that had been mainly degraded by parasitic attack, taken from the Cabinet of Scientific Research for the Cultural Heritage of Vatican Museums. The pieces of wood (_Populus_ spp.) were cut to obtain a size of 20 \(\times\) 2 \(\times\) 80 mm\({}^{3}\) (width \(\times\) thickness \(\times\) length). Each consolidating product was used to treat the three wood samples, and an untreated sample was taken as a reference. Therefore, the nine treated samples were divided into three groups: A, B, C, corresponding, respectively, to the samples treated with CNC (A1, A2, A3), Paraloid B-72 (B1, B2, B3), and Regalrez 1126 (C1, C2, C3). The untreated sample was indicated by the abbreviation NT. The wood samples were treated with about 1 mL of the consolidating mixtures, described below, by brushing with three consecutive applications on each sample.  
The consolidating agents used were:  
* Aqueous suspension of cellulose nanocrystals (CNC), used as synthesized;
* Paraloid B-72 and Regalrez 1126 were dissolved in 10% acetone and in 15% white spirit, respectively, and applied.  
All wood samples were weighed before the treatment, after 19 h, and one month later (Table 1).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Before** & **After 19 h** & **After 1 Month** \\ \hline A1 & 1.343 g & 1.356 g & 1.342 g \\ \hline A2 & 1.021 g & 1.031 g & 1.020 g \\ \hline A3 & 1.301 g & 1.312 g & 1.298 g \\ \hline B1 & 1.280 g & 1.406 g & 1.392 g \\ \hline B2 & 1.305 g & 1.408 g & 1.396 g \\ \hline B3 & 0.974 g & 1.061 g & 1.050 g \\ \hline C1 & 0.989 g & 1.073 g & 1.061 g \\ \hline \end{tabular}
\end{table}
Table 1: Weights of the samples before the application of consolidants, after 19 h, and after one month.  
All applications were carried out by total impregnation under the hood at a temperature of about 23.5 \({}^{\circ}\)C and relative humidity value (RH) equal to 32.1%. Once the treatment was carried out, the samples were left in the hood under the previous controlled conditions, pending characterization.