# Spanish Poplar Biomass as a Precursor for Nanocellulose Extraction
## 3 Results and Discussions
Nanocellulose extraction was performed by mechanical means to yield nanofibrils or  
Figure 4: XRD characterization 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. chemical means to extract nanocrystals, or a combination of both means. Mechanical extraction comprised probe sonication and disc grinding; chemical extraction was either acidic reaction (H2 SO4) or enzymatic hydrolysis applying cellulase enzyme. Disc grinding yielded smaller sized particles than probe sonication; cellulose nanofibrils from grinding showed 20-30 nm [47] and 18.5 nm [49], whereas probe sonication yielded 15-70 nm [50] and 20-90 nm [51]. Acidic hydrolysis resulted in smaller sized particles than mechanical extraction, with 11.4 nm diameter [50] and 69 nm (this study). Only enzymolysis yielded extremely large size particles of 300 nm [48], which does not promote this method as a poplar nanocellulose extraction technique. As expected, CNC resulting from acidic hydrolysis showed higher crystallinity than CNF. The interpretation is that acidic hydrolysis targets amorphous regions, boosting up the percentage of the crystalline part. Comparing this study to the literature, especially [49], we can find that more effort should have been exerted in pulping and bleaching. In [49], there were five bleaching processes followed by pulping, then bleaching, and finally pulping again. This allows to interpret the smaller size of the resulting CNC and its higher crystallinity compared to this study. \begin{table}
\begin{tabular}{c c c c c c} \hline  & \multicolumn{2}{c}{**Cellulose Purification**} & \multicolumn{2}{c}{**Nanocellulose**} & \multirow{2}{*}{**Size**} & \multirow{2}{*}{**IR and Crystallinity**} \\ \cline{2-2} \cline{6-6}  & **Step 1** & & & & \\ \hline \multirow{6}{*}{poplar} & NaClO2 for 1 h & \multirow{6}{*}{NaClO2 for 2 h} & 0.3 wt\% disc & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } \\  & (6 times) & & & grinder 1500 r/min & & FTIR \\  & then & & Then & & - Lignin removal \\  & then & 5 wt\% KOH & 5 wt\% KOH & high-pressure & 20–30 nm & Crystallinity \\  & 2 wt\% KOH & 90 \({}^{\circ}\)C for 2 h & & homogenizer & \\  & 90 \({}^{\circ}\)C for 2 h & & 700 bar then 100 & & CNC pop. 60\% \\  & & & bar 30 min & & \\ \hline \multirow{6}{*}{poplar} & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } & Enzymolysis & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } \\  & Steam & NaClO2 & Cellulose (diff time, & \\  & explosion & (9.7 g/L) for 1 h & temp, and conc) & CNC & - Lignin removal \\  & 2 MPa 180 s & at 75 \({}^{\circ}\)C & Then & 310 nm & Crystallinity \\  & & & Probe sonicator & & Native pop. 45\% \\  & & & 20 min, 200 W & & CNC pop. 62\% \\ \hline \multirow{6}{*}{poplar} & NaClO2 70 \({}^{\circ}\)C & NaClO2 70 \({}^{\circ}\)C & 64 wt\% H2 SO4 & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } \\  & for 1 h & 45 \({}^{\circ}\)C for 30 min & CNC & - Lignin removal \\  & (5 times) & Then & (OR) & 11.4/153.2 nm & -SO4 group for CNC \\  & Then & & 1\% wt disk grinder & CNF & Native pop. 56.1\% \\  & 5 wt\% NaOH & & 1500 rpm for & 18.5 nm & CNC pop. 72.9\% \\  & at 90 \({}^{\circ}\)C for 2 h & & 5 times & & CNF pop. 56.4\% \\ \hline \multirow{6}{*}{Poplar Catkin Fiber} & 1\% NaClO2 at & 2 wt\% NaOH & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } \\  & 1\% NaClO2 at & 1\% wt soln & 15–70 nm & \\  & 75 \({}^{\circ}\)C 1 h & & 600 w & 5 min more & FTIR \\  & (repeat 3 times) & 5 wt\% NaOH & 19.5–20.5 kHz & sonication & Lignin removal \\  & & at 90 \({}^{\circ}\)C & & 5 nm & \\  & & & & 5 nm & \\ \hline \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } & \multirow{6}{*}{ \begin{tabular}{} \end{tabular}  } & NaClO2 100 \({}^{\circ}\)C, acidic medium. & 60\% H2 SO4, 40 \({}^{\circ}\)C & CNC & Crystallinity \\  & 120 \({}^{\circ}\)C, 2 h & (3–4 times) & & 69 nm & Native 58\% \\ \cline{1-1}  & & & & CNC 65\% & \\ \hline \multirow{6}{*}{