## 3 Results and Discussion
### Molecular Weight Analysis of ODA and DA Lignin Samples  
In order to further determine the molecular weight of the lignin extracted at the optimum conditions, named as optimum dioxane acetic acid (ODA) lignin and the previously sorted DA lignin, the GPC analysis was also performed. For the reference, milled wood lignin was also analyzed and the results are reported in Table 4. For the results of their molecular weights, the values are in comparison within each other but almost half of the milled wood lignin in terms of their weight average (M\({}_{\text{w}}\)) value. Regarding their polydispersity values it was improved from 1.90 for DA lignin to 1.65 for ODA lignin. This is also somewhat expected under our adapted conditions as the low catalyst dose released less amount of lignin to be released but a high dose also helped to increase the yield but also led to the formation of more lower molecular weight fractions and this was also evident from our model values. As it can be seen in the table, the molecular weight of ODA lignin was quite high with a value of 4358 and a corresponding polydispersity of 1.65 but as expected the values for DA lignin were 4718 and 1.90, respectively. As compared with the milled wood lignin, it has high value of polydispersity of 2.06 and the molecular weight was 10,660 units almost double the extracted lignin. These values are in a fair comparison with the previously published literature. For example, in one such previous study, a mixture of ethanol/water (50/50 \(w/w\)) catalyzed by 1.2% \(w/w\) H\({}_{2}\)SO\({}_{4}\) was used at 180 \({}^{\circ}\)C and 1 h of time to isolate the lignin from eucalyptus showed a molecular weight value of 5079 but with a rather higher polydispersity of 3.24 [49]. In another study, the acetic acid (87% aqueous \(w/w\)) catalyzed by HCI (0.6 gm of 36% \(w/w\) HCI) 114 \({}^{\circ}\)C for 80 min was used to extract lignin from bamboo shoot shell and this lignin also exhibited a quite low molecular weight of 2789 with 1.54 of improved polydispersity quite closed to our ODA lignin value (1.65) [50]. Similarly, acetosyl lignin isolated from siam weed stem at 107 \({}^{\circ}\)C for 3 h of time employing 93% acetic acid-water \(v/v\) with 0.1% (\(w/w\) of liquid phase) HCI as catalyst showed a high polydispersity of 2.83 but with rather low molecular weight of 2010 [27].  
For the GPC chromatograms, all of the three lignin samples exhibited the homogeneous curves showing their relative unique nature (Figure 2). In one of our previous studies, when the GVL was employed as a reagent for milled wood pine saw dust, the polydispersity was considerably high in the range of 2.54-2.96 but under this process condition the polydispersity was noticeably improved [51]. From here it can be anticipated that the thermal conditions may lead to a harsher condition for the lignin isolation even under mild reagent conditions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scheme 3** & **M\({}_{\text{w}}\)** & **M\({}_{\text{n}}\)** & **(M\({}_{\text{w}}\)/M\({}_{\text{n}}\)) P** \\ \hline MWL & 10,660 & 5157 & 2.06 \\ ODA lignin & 4358 & 2641 & 1.65 \\ DA lignin & 4718 & 2473 & 1.90 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Molecular weights of Optimum Dioxane, Dioxane & Milled Wood Lignin (ODA, DA, and MWL samples).