# Spanish Poplar Biomass as a Precursor for Nanocellulose Extraction
## 3 Results and Discussions
This can be attributed to the lower diameter of nanocellulose, which implies a larger specific area and therefore a larger number of hydroxyl group [43]. Native poplar in Figure 3A showed a unique peak at 1601 cm\({}^{-1}\) (which does not appear in treated fibers) corresponding to C=C unsaturated components. At 2890 cm\({}^{-1}\), the H-C-H group peak became more intense after hydrolysis (compare Figure 3A,B), probably because of the same reason as for the OH group. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & \multicolumn{3}{c}{**Poplar**} & \multicolumn{3}{c}{**MCC**} \\ \hline  & \multicolumn{2}{c}{**Length**} & \multicolumn{2}{c}{**Width**} & \multicolumn{2}{c}{**Length**} & \multicolumn{2}{c}{**Width**} \\ \hline Processing time (min) & 5 & 15 & 5 & 15 & 5 & 10 & 5 & 10 \\ \hline Average (nm) & 371.7 & 218.8 & 131.1 & 68.8 & 141.5 & 122 & 39.9 & 19.9 \\ \hline Std. dev. (nm) & 192.1 & 172.1 & 88.8 & 37 & 42 & 34.5 & 12.7 & 5.1 \\ \hline Max. (nm) & 922 & 815 & 402 & 157 & 232 & 208 & 77 & 29 \\ \hline Min. (nm) & 100 & 56 & 23 & 21 & 66 & 52 & 19 & 9 \\ \hline \end{tabular}
\end{table} 
Table 1: Size distribution (length and width) of cellulose nanocrystals (CNC), sourced from either poplar or microcrystalline cellulose (MCC), measured from TEM photos showcased previously. Figure 3: _Cont._  
Crystallinity was characterized by XRD technique, and the results were showcased in Figure 4. This is as explained in [44]. Cellulose diffractograms showed the following peaks: 20 = 12.5\({}^{\circ}\) (for 1 1 0 plane), labeled \"1\" in Figure 4, 20 = 15.5\({}^{\circ}\) (for 1 0 1 plane), labeled \"2\", 20 = 16.5\({}^{\circ}\) (for 1 0 1 plane), labeled \"3\", 20 = 19.5\({}^{\circ}\) (for 0 2 1 plane), labeled \"4\", 20 = 22.5\({}^{\circ}\) (for 2 0 0 plane), labeled \"5\", 20 = 34.5\({}^{\circ}\) (for 0 4 0 plane), labeled \"6\". In this investigation, all types of non-hydrolyzed cellulose (native poplar, pulped poplar, bleached poplar, and MCC), exhibited two peaks, a low one at 20 = 15.5\({}^{\circ}\) (overlapping with 20 = 16.5\({}^{\circ}\)) and a higher one at 20 = 22.5\({}^{\circ}\); additionally, MCC showed small peaks at 20 = 19.5 and 20 = 34.5\({}^{\circ}\). All hydrolyzed samples, called cellulose nanocrystals (CNC), depicted the similar peak location as non hydrolyzed samples. However, contrary to non-hydrolyzed samples, peak 1 was quite clear, and peak 4 was significantly higher than peak 5, forming doublet shaped peak, the pattern which is documented elsewhere for nanocellulose [35; 45; 46]. Doublet peaks corroborate the existence of two cellulose polymorphs, namely cellulose I (represented by I22.5) and cellulose II (represented by I19.5) [35]. The higher peak at 20 = 19.5\({}^{\circ}\) of hydrolyzed cellulose (nanocellulose) in our work suggests that the content of cellulose II was higher than that of cellulose I.  
Figure 3: FTIR spectral investigations of (**A**) Native, pulped, and bleached poplar, (**B**) Cellulose nanocrystals (CNC) sourced from poplar after 4, 10, and 15 min of hydrolysis, and (**C**) microcrystalline cellulose (MCC) and CNC sourced from MCC after 5 and 10 min of hydrolysis. In Table 2, the efforts to extract poplar nanocellulose are summarized, which were published by incidence during the last year. Conventional poplar residues were mainly used; however, two attempts were performed on poplar catkin fibers and APMP. Cellulose purification was carried out commencing with bleaching (using NaClO\({}_{2}\)) for lignin removal, then pulping using alkali to remove hemicellulose. In some cases, repeated cycles of bleaching and pulping combined were carried out [47]. Only one article show-cased steam explosion to remove hemicellulose and to activate lignocellulosic texture [48].