Effect of pretreatment (organosolv extraction, ultrasonic treatment, and NaOH treat­ment) on the microstructure of pine sawdust was analyzed using SEM. Comparison of the changes in microstructure of pine sawdust before and after the organosolv extraction pretreatment is shown in Fig. 19.1a-d. The SEM pictures clearly show that the microstructure of pine sawdust changed after pretreatments. Compared with the nicely presented cell wall structure in the raw pine sawdust, the pretreatments led to a significant swelling of the raw pine sawdust and caused disorder in the cell structure. After pretreatment, the cell wall seems to be destroyed. The original cell wall was twisted and disordered, suggesting that significant morphological changes occurred in the process. Similarly, the raw pine sawdust sample exhibited rigid and highly ordered fibrils. The fibers of pine sawdust samples after pretreatment were distorted and twisted. The microfibrils were also isolated from the initial connected structure and made fully exposable, thus increasing the external surface area and the porosity of the biomass structure.

From the XRD measurement of pine sawdust before and after the various types of pretreatments, there are three peaks occurring at 26 of 14.6 °, 16.5 °, and 22.4 ° with varying intensities. These peaks correspond to cellulose XRD, corresponding to cellulose’s crystalline planes of (1Ї0), (110) and (220), respectively [52]. Compared with the un-treated raw material, the cellulose peaks all increase considerably in the pretreated pine sawdust samples. This demonstrates that the concentration of cellulose in the residues after pretreatment increases owing to the removal of hemi — cellulose and lignin in the pretreatment processes. The intensity of the cellulose peaks in sawdust samples increases with an increase in the PE and DE, which is expected as the cellulose content in the pretreated sawdust samples increased with an increase in the PE and DE. The CrI calculated from the Eq. 19.5 is 43 %, 63 %, 55 %, 64 %, and 65 %, respectively, for the untreated sawdust sample and the pretreated samples with the organosolv extraction, organosolv + NaOH, organosolv + ultrasound and organosolv + NaOH + ultrasound. As a common observation from chemical or

organosolv pretreatment of biomass [32, 49], crystallinity of the pretreated samples increases due to the removal of hemicelluloses and lignin. However, it should be noted that an increase in crystallinity of pretreated material was not expected to negatively affect the product yield during enzymatic hydrolysis of biomass [32,49].

The functional groups of the raw and pretreated sawdust samples, as well as pure cellulose and pure lignin were characterized using the FTIR technique (while the IR spectra are not included in this chapter). The FTIR results show that the pretreated sawdust samples are very similar to the peak patterns of the pure cellulose in the whole wavenumber range, simply because the cellulose content is high in pretreated sawdust samples when compared to the raw pine sawdust. The absorption bands at 1,275 cm-1 and 1,516-1,700 cm-1 correspond to the functional groups of lignin. The absorption band at 1,275 cm-1 is related to vibrations of guaiacyl rings and the absorption bands at 1,516-1,700 cm-1 ascribe to aromatic ring vibrations. The pure lignin and raw pine sawdust materials possess stronger signal at these absorption band, due to the higher content of lignin. The pretreated pine sawdust had a weaker signal at these absorption bands, because the majority of lignin was removed by the pretreatment. The absorption band at 1,711 cm-1 is related to carbonyl absorption in hemicelluloses. The raw and pretreated pine sawdust samples all showed absorption at 1,711 cm-1, implying that the pretreatment were unable to remove all hemicellu — lose in the raw materials, as also reported by Sreenivasan et al. [53]. In summary, the FTIR measurement indicated that the pretreatment was more efficient for removing of lignin than hemicellulose and cellulose from the pine sawdust.